| Server IP : 85.214.239.14 / Your IP : 3.148.144.100 Web Server : Apache/2.4.61 (Debian) System : Linux h2886529.stratoserver.net 4.9.0 #1 SMP Tue Jan 9 19:45:01 MSK 2024 x86_64 User : www-data ( 33) PHP Version : 7.4.18 Disable Function : pcntl_alarm,pcntl_fork,pcntl_waitpid,pcntl_wait,pcntl_wifexited,pcntl_wifstopped,pcntl_wifsignaled,pcntl_wifcontinued,pcntl_wexitstatus,pcntl_wtermsig,pcntl_wstopsig,pcntl_signal,pcntl_signal_get_handler,pcntl_signal_dispatch,pcntl_get_last_error,pcntl_strerror,pcntl_sigprocmask,pcntl_sigwaitinfo,pcntl_sigtimedwait,pcntl_exec,pcntl_getpriority,pcntl_setpriority,pcntl_async_signals,pcntl_unshare, MySQL : OFF | cURL : OFF | WGET : ON | Perl : ON | Python : ON | Sudo : ON | Pkexec : OFF Directory : /proc/3/cwd/usr/share/doc/nodejs/api/ |
Upload File : |
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width">
<meta name="nodejs.org:node-version" content="v20.15.1">
<title>Util | Node.js v20.15.1 Documentation</title>
<link rel="stylesheet" href="https://fonts.googleapis.com/css?family=Lato:400,700,400italic&display=fallback">
<link rel="stylesheet" href="assets/style.css">
<link rel="stylesheet" href="assets/hljs.css">
<link rel="canonical" href="https://nodejs.org/api/util.html">
<script async defer src="assets/api.js" type="text/javascript"></script>
<script>
const storedTheme = localStorage.getItem('theme');
// Follow operating system theme preference
if (storedTheme === null && window.matchMedia) {
const mq = window.matchMedia('(prefers-color-scheme: dark)');
if (mq.matches) {
document.documentElement.classList.add('dark-mode');
}
} else if (storedTheme === 'dark') {
document.documentElement.classList.add('dark-mode');
}
</script>
<style>@media(max-width:558px){.with-42-chars>.js-flavor-toggle{float:none;margin:0 0 1em auto;}}@media(max-width:718px){.with-62-chars>.js-flavor-toggle{float:none;margin:0 0 1em auto;}}@media(max-width:574px){.with-44-chars>.js-flavor-toggle{float:none;margin:0 0 1em auto;}}@media(max-width:566px){.with-43-chars>.js-flavor-toggle{float:none;margin:0 0 1em auto;}}@media(max-width:662px){.with-55-chars>.js-flavor-toggle{float:none;margin:0 0 1em auto;}}@media(max-width:550px){.with-41-chars>.js-flavor-toggle{float:none;margin:0 0 1em auto;}}</style>
</head>
<body class="alt apidoc" id="api-section-util">
<div id="content" class="clearfix">
<div role="navigation" id="column2" class="interior">
<div id="intro" class="interior">
<a href="/" title="Go back to the home page">
Node.js
</a>
</div>
<ul>
<li><a href="documentation.html" class="nav-documentation">About this documentation</a></li>
<li><a href="synopsis.html" class="nav-synopsis">Usage and example</a></li>
</ul>
<hr class="line">
<ul>
<li><a href="assert.html" class="nav-assert">Assertion testing</a></li>
<li><a href="async_context.html" class="nav-async_context">Asynchronous context tracking</a></li>
<li><a href="async_hooks.html" class="nav-async_hooks">Async hooks</a></li>
<li><a href="buffer.html" class="nav-buffer">Buffer</a></li>
<li><a href="addons.html" class="nav-addons">C++ addons</a></li>
<li><a href="n-api.html" class="nav-n-api">C/C++ addons with Node-API</a></li>
<li><a href="embedding.html" class="nav-embedding">C++ embedder API</a></li>
<li><a href="child_process.html" class="nav-child_process">Child processes</a></li>
<li><a href="cluster.html" class="nav-cluster">Cluster</a></li>
<li><a href="cli.html" class="nav-cli">Command-line options</a></li>
<li><a href="console.html" class="nav-console">Console</a></li>
<li><a href="corepack.html" class="nav-corepack">Corepack</a></li>
<li><a href="crypto.html" class="nav-crypto">Crypto</a></li>
<li><a href="debugger.html" class="nav-debugger">Debugger</a></li>
<li><a href="deprecations.html" class="nav-deprecations">Deprecated APIs</a></li>
<li><a href="diagnostics_channel.html" class="nav-diagnostics_channel">Diagnostics Channel</a></li>
<li><a href="dns.html" class="nav-dns">DNS</a></li>
<li><a href="domain.html" class="nav-domain">Domain</a></li>
<li><a href="errors.html" class="nav-errors">Errors</a></li>
<li><a href="events.html" class="nav-events">Events</a></li>
<li><a href="fs.html" class="nav-fs">File system</a></li>
<li><a href="globals.html" class="nav-globals">Globals</a></li>
<li><a href="http.html" class="nav-http">HTTP</a></li>
<li><a href="http2.html" class="nav-http2">HTTP/2</a></li>
<li><a href="https.html" class="nav-https">HTTPS</a></li>
<li><a href="inspector.html" class="nav-inspector">Inspector</a></li>
<li><a href="intl.html" class="nav-intl">Internationalization</a></li>
<li><a href="modules.html" class="nav-modules">Modules: CommonJS modules</a></li>
<li><a href="esm.html" class="nav-esm">Modules: ECMAScript modules</a></li>
<li><a href="module.html" class="nav-module">Modules: <code>node:module</code> API</a></li>
<li><a href="packages.html" class="nav-packages">Modules: Packages</a></li>
<li><a href="net.html" class="nav-net">Net</a></li>
<li><a href="os.html" class="nav-os">OS</a></li>
<li><a href="path.html" class="nav-path">Path</a></li>
<li><a href="perf_hooks.html" class="nav-perf_hooks">Performance hooks</a></li>
<li><a href="permissions.html" class="nav-permissions">Permissions</a></li>
<li><a href="process.html" class="nav-process">Process</a></li>
<li><a href="punycode.html" class="nav-punycode">Punycode</a></li>
<li><a href="querystring.html" class="nav-querystring">Query strings</a></li>
<li><a href="readline.html" class="nav-readline">Readline</a></li>
<li><a href="repl.html" class="nav-repl">REPL</a></li>
<li><a href="report.html" class="nav-report">Report</a></li>
<li><a href="single-executable-applications.html" class="nav-single-executable-applications">Single executable applications</a></li>
<li><a href="stream.html" class="nav-stream">Stream</a></li>
<li><a href="string_decoder.html" class="nav-string_decoder">String decoder</a></li>
<li><a href="test.html" class="nav-test">Test runner</a></li>
<li><a href="timers.html" class="nav-timers">Timers</a></li>
<li><a href="tls.html" class="nav-tls">TLS/SSL</a></li>
<li><a href="tracing.html" class="nav-tracing">Trace events</a></li>
<li><a href="tty.html" class="nav-tty">TTY</a></li>
<li><a href="dgram.html" class="nav-dgram">UDP/datagram</a></li>
<li><a href="url.html" class="nav-url">URL</a></li>
<li><a href="util.html" class="nav-util active">Utilities</a></li>
<li><a href="v8.html" class="nav-v8">V8</a></li>
<li><a href="vm.html" class="nav-vm">VM</a></li>
<li><a href="wasi.html" class="nav-wasi">WASI</a></li>
<li><a href="webcrypto.html" class="nav-webcrypto">Web Crypto API</a></li>
<li><a href="webstreams.html" class="nav-webstreams">Web Streams API</a></li>
<li><a href="worker_threads.html" class="nav-worker_threads">Worker threads</a></li>
<li><a href="zlib.html" class="nav-zlib">Zlib</a></li>
</ul>
<hr class="line">
<ul>
<li><a href="https://github.com/nodejs/node" class="nav-https-github-com-nodejs-node">Code repository and issue tracker</a></li>
</ul>
</div>
<div id="column1" data-id="util" class="interior">
<header class="header">
<div class="header-container">
<h1>Node.js v20.15.1 documentation</h1>
<button class="theme-toggle-btn" id="theme-toggle-btn" title="Toggle dark mode/light mode" aria-label="Toggle dark mode/light mode" hidden>
<svg xmlns="http://www.w3.org/2000/svg" class="icon dark-icon" height="24" width="24">
<path fill="none" d="M0 0h24v24H0z" />
<path d="M11.1 12.08c-2.33-4.51-.5-8.48.53-10.07C6.27 2.2 1.98 6.59 1.98 12c0 .14.02.28.02.42.62-.27 1.29-.42 2-.42 1.66 0 3.18.83 4.1 2.15A4.01 4.01 0 0111 18c0 1.52-.87 2.83-2.12 3.51.98.32 2.03.5 3.11.5 3.5 0 6.58-1.8 8.37-4.52-2.36.23-6.98-.97-9.26-5.41z"/>
<path d="M7 16h-.18C6.4 14.84 5.3 14 4 14c-1.66 0-3 1.34-3 3s1.34 3 3 3h3c1.1 0 2-.9 2-2s-.9-2-2-2z"/>
</svg>
<svg xmlns="http://www.w3.org/2000/svg" class="icon light-icon" height="24" width="24">
<path d="M0 0h24v24H0z" fill="none" />
<path d="M6.76 4.84l-1.8-1.79-1.41 1.41 1.79 1.79 1.42-1.41zM4 10.5H1v2h3v-2zm9-9.95h-2V3.5h2V.55zm7.45 3.91l-1.41-1.41-1.79 1.79 1.41 1.41 1.79-1.79zm-3.21 13.7l1.79 1.8 1.41-1.41-1.8-1.79-1.4 1.4zM20 10.5v2h3v-2h-3zm-8-5c-3.31 0-6 2.69-6 6s2.69 6 6 6 6-2.69 6-6-2.69-6-6-6zm-1 16.95h2V19.5h-2v2.95zm-7.45-3.91l1.41 1.41 1.79-1.8-1.41-1.41-1.79 1.8z"/>
</svg>
</button>
</div>
<div id="gtoc">
<ul>
<li class="pinned-header">Node.js v20.15.1</li>
<li class="picker-header">
<a href="#">
<span class="picker-arrow"></span>
Table of contents
</a>
<div class="picker"><div class="toc"><ul>
<li><span class="stability_2"><a href="#util">Util</a></span>
<ul>
<li><a href="#utilcallbackifyoriginal"><code>util.callbackify(original)</code></a></li>
<li><a href="#utildebuglogsection-callback"><code>util.debuglog(section[, callback])</code></a>
<ul>
<li><a href="#debuglogenabled"><code>debuglog().enabled</code></a></li>
</ul>
</li>
<li><a href="#utildebugsection"><code>util.debug(section)</code></a></li>
<li><a href="#utildeprecatefn-msg-code"><code>util.deprecate(fn, msg[, code])</code></a></li>
<li><a href="#utilformatformat-args"><code>util.format(format[, ...args])</code></a></li>
<li><a href="#utilformatwithoptionsinspectoptions-format-args"><code>util.formatWithOptions(inspectOptions, format[, ...args])</code></a></li>
<li><a href="#utilgetsystemerrornameerr"><code>util.getSystemErrorName(err)</code></a></li>
<li><a href="#utilgetsystemerrormap"><code>util.getSystemErrorMap()</code></a></li>
<li><span class="stability_3"><a href="#utilinheritsconstructor-superconstructor"><code>util.inherits(constructor, superConstructor)</code></a></span></li>
<li><a href="#utilinspectobject-options"><code>util.inspect(object[, options])</code></a></li>
<li><a href="#utilinspectobject-showhidden-depth-colors"><code>util.inspect(object[, showHidden[, depth[, colors]]])</code></a>
<ul>
<li><a href="#customizing-utilinspect-colors">Customizing <code>util.inspect</code> colors</a>
<ul>
<li><a href="#modifiers">Modifiers</a></li>
<li><a href="#foreground-colors">Foreground colors</a></li>
<li><a href="#background-colors">Background colors</a></li>
</ul>
</li>
<li><a href="#custom-inspection-functions-on-objects">Custom inspection functions on objects</a></li>
<li><a href="#utilinspectcustom"><code>util.inspect.custom</code></a></li>
<li><a href="#utilinspectdefaultoptions"><code>util.inspect.defaultOptions</code></a></li>
</ul>
</li>
<li><a href="#utilisdeepstrictequalval1-val2"><code>util.isDeepStrictEqual(val1, val2)</code></a></li>
<li><span class="stability_1"><a href="#class-utilmimetype">Class: <code>util.MIMEType</code></a></span>
<ul>
<li><a href="#constructor-new-mimetypeinput">Constructor: <code>new MIMEType(input)</code></a></li>
<li><a href="#mimetype"><code>mime.type</code></a></li>
<li><a href="#mimesubtype"><code>mime.subtype</code></a></li>
<li><a href="#mimeessence"><code>mime.essence</code></a></li>
<li><a href="#mimeparams"><code>mime.params</code></a></li>
<li><a href="#mimetostring"><code>mime.toString()</code></a></li>
<li><a href="#mimetojson"><code>mime.toJSON()</code></a></li>
</ul>
</li>
<li><a href="#class-utilmimeparams">Class: <code>util.MIMEParams</code></a>
<ul>
<li><a href="#constructor-new-mimeparams">Constructor: <code>new MIMEParams()</code></a></li>
<li><a href="#mimeparamsdeletename"><code>mimeParams.delete(name)</code></a></li>
<li><a href="#mimeparamsentries"><code>mimeParams.entries()</code></a></li>
<li><a href="#mimeparamsgetname"><code>mimeParams.get(name)</code></a></li>
<li><a href="#mimeparamshasname"><code>mimeParams.has(name)</code></a></li>
<li><a href="#mimeparamskeys"><code>mimeParams.keys()</code></a></li>
<li><a href="#mimeparamssetname-value"><code>mimeParams.set(name, value)</code></a></li>
<li><a href="#mimeparamsvalues"><code>mimeParams.values()</code></a></li>
<li><a href="#mimeparamsiterator"><code>mimeParams[@@iterator]()</code></a></li>
</ul>
</li>
<li><a href="#utilparseargsconfig"><code>util.parseArgs([config])</code></a>
<ul>
<li><a href="#parseargs-tokens"><code>parseArgs</code> <code>tokens</code></a></li>
</ul>
</li>
<li><span class="stability_1"><a href="#utilparseenvcontent"><code>util.parseEnv(content)</code></a></span></li>
<li><a href="#utilpromisifyoriginal"><code>util.promisify(original)</code></a>
<ul>
<li><a href="#custom-promisified-functions">Custom promisified functions</a></li>
<li><a href="#utilpromisifycustom"><code>util.promisify.custom</code></a></li>
</ul>
</li>
<li><a href="#utilstripvtcontrolcharactersstr"><code>util.stripVTControlCharacters(str)</code></a></li>
<li><span class="stability_1"><a href="#utilstyletextformat-text"><code>util.styleText(format, text)</code></a></span></li>
<li><a href="#class-utiltextdecoder">Class: <code>util.TextDecoder</code></a>
<ul>
<li><a href="#whatwg-supported-encodings">WHATWG supported encodings</a>
<ul>
<li><a href="#encodings-supported-by-default-with-full-icu-data">Encodings supported by default (with full ICU data)</a></li>
<li><a href="#encodings-supported-when-nodejs-is-built-with-the-small-icu-option">Encodings supported when Node.js is built with the <code>small-icu</code> option</a></li>
<li><a href="#encodings-supported-when-icu-is-disabled">Encodings supported when ICU is disabled</a></li>
</ul>
</li>
<li><a href="#new-textdecoderencoding-options"><code>new TextDecoder([encoding[, options]])</code></a></li>
<li><a href="#textdecoderdecodeinput-options"><code>textDecoder.decode([input[, options]])</code></a></li>
<li><a href="#textdecoderencoding"><code>textDecoder.encoding</code></a></li>
<li><a href="#textdecoderfatal"><code>textDecoder.fatal</code></a></li>
<li><a href="#textdecoderignorebom"><code>textDecoder.ignoreBOM</code></a></li>
</ul>
</li>
<li><a href="#class-utiltextencoder">Class: <code>util.TextEncoder</code></a>
<ul>
<li><a href="#textencoderencodeinput"><code>textEncoder.encode([input])</code></a></li>
<li><a href="#textencoderencodeintosrc-dest"><code>textEncoder.encodeInto(src, dest)</code></a></li>
<li><a href="#textencoderencoding"><code>textEncoder.encoding</code></a></li>
</ul>
</li>
<li><a href="#utiltousvstringstring"><code>util.toUSVString(string)</code></a></li>
<li><span class="stability_1"><a href="#utiltransferableabortcontroller"><code>util.transferableAbortController()</code></a></span></li>
<li><span class="stability_1"><a href="#utiltransferableabortsignalsignal"><code>util.transferableAbortSignal(signal)</code></a></span></li>
<li><span class="stability_1"><a href="#utilabortedsignal-resource"><code>util.aborted(signal, resource)</code></a></span></li>
<li><a href="#utiltypes"><code>util.types</code></a>
<ul>
<li><a href="#utiltypesisanyarraybuffervalue"><code>util.types.isAnyArrayBuffer(value)</code></a></li>
<li><a href="#utiltypesisarraybufferviewvalue"><code>util.types.isArrayBufferView(value)</code></a></li>
<li><a href="#utiltypesisargumentsobjectvalue"><code>util.types.isArgumentsObject(value)</code></a></li>
<li><a href="#utiltypesisarraybuffervalue"><code>util.types.isArrayBuffer(value)</code></a></li>
<li><a href="#utiltypesisasyncfunctionvalue"><code>util.types.isAsyncFunction(value)</code></a></li>
<li><a href="#utiltypesisbigint64arrayvalue"><code>util.types.isBigInt64Array(value)</code></a></li>
<li><a href="#utiltypesisbiguint64arrayvalue"><code>util.types.isBigUint64Array(value)</code></a></li>
<li><a href="#utiltypesisbooleanobjectvalue"><code>util.types.isBooleanObject(value)</code></a></li>
<li><a href="#utiltypesisboxedprimitivevalue"><code>util.types.isBoxedPrimitive(value)</code></a></li>
<li><a href="#utiltypesiscryptokeyvalue"><code>util.types.isCryptoKey(value)</code></a></li>
<li><a href="#utiltypesisdataviewvalue"><code>util.types.isDataView(value)</code></a></li>
<li><a href="#utiltypesisdatevalue"><code>util.types.isDate(value)</code></a></li>
<li><a href="#utiltypesisexternalvalue"><code>util.types.isExternal(value)</code></a></li>
<li><a href="#utiltypesisfloat32arrayvalue"><code>util.types.isFloat32Array(value)</code></a></li>
<li><a href="#utiltypesisfloat64arrayvalue"><code>util.types.isFloat64Array(value)</code></a></li>
<li><a href="#utiltypesisgeneratorfunctionvalue"><code>util.types.isGeneratorFunction(value)</code></a></li>
<li><a href="#utiltypesisgeneratorobjectvalue"><code>util.types.isGeneratorObject(value)</code></a></li>
<li><a href="#utiltypesisint8arrayvalue"><code>util.types.isInt8Array(value)</code></a></li>
<li><a href="#utiltypesisint16arrayvalue"><code>util.types.isInt16Array(value)</code></a></li>
<li><a href="#utiltypesisint32arrayvalue"><code>util.types.isInt32Array(value)</code></a></li>
<li><a href="#utiltypesiskeyobjectvalue"><code>util.types.isKeyObject(value)</code></a></li>
<li><a href="#utiltypesismapvalue"><code>util.types.isMap(value)</code></a></li>
<li><a href="#utiltypesismapiteratorvalue"><code>util.types.isMapIterator(value)</code></a></li>
<li><a href="#utiltypesismodulenamespaceobjectvalue"><code>util.types.isModuleNamespaceObject(value)</code></a></li>
<li><a href="#utiltypesisnativeerrorvalue"><code>util.types.isNativeError(value)</code></a></li>
<li><a href="#utiltypesisnumberobjectvalue"><code>util.types.isNumberObject(value)</code></a></li>
<li><a href="#utiltypesispromisevalue"><code>util.types.isPromise(value)</code></a></li>
<li><a href="#utiltypesisproxyvalue"><code>util.types.isProxy(value)</code></a></li>
<li><a href="#utiltypesisregexpvalue"><code>util.types.isRegExp(value)</code></a></li>
<li><a href="#utiltypesissetvalue"><code>util.types.isSet(value)</code></a></li>
<li><a href="#utiltypesissetiteratorvalue"><code>util.types.isSetIterator(value)</code></a></li>
<li><a href="#utiltypesissharedarraybuffervalue"><code>util.types.isSharedArrayBuffer(value)</code></a></li>
<li><a href="#utiltypesisstringobjectvalue"><code>util.types.isStringObject(value)</code></a></li>
<li><a href="#utiltypesissymbolobjectvalue"><code>util.types.isSymbolObject(value)</code></a></li>
<li><a href="#utiltypesistypedarrayvalue"><code>util.types.isTypedArray(value)</code></a></li>
<li><a href="#utiltypesisuint8arrayvalue"><code>util.types.isUint8Array(value)</code></a></li>
<li><a href="#utiltypesisuint8clampedarrayvalue"><code>util.types.isUint8ClampedArray(value)</code></a></li>
<li><a href="#utiltypesisuint16arrayvalue"><code>util.types.isUint16Array(value)</code></a></li>
<li><a href="#utiltypesisuint32arrayvalue"><code>util.types.isUint32Array(value)</code></a></li>
<li><a href="#utiltypesisweakmapvalue"><code>util.types.isWeakMap(value)</code></a></li>
<li><a href="#utiltypesisweaksetvalue"><code>util.types.isWeakSet(value)</code></a></li>
</ul>
</li>
<li><a href="#deprecated-apis">Deprecated APIs</a>
<ul>
<li><span class="stability_0"><a href="#util_extendtarget-source"><code>util._extend(target, source)</code></a></span></li>
<li><span class="stability_0"><a href="#utilisarrayobject"><code>util.isArray(object)</code></a></span></li>
<li><span class="stability_0"><a href="#utilisbooleanobject"><code>util.isBoolean(object)</code></a></span></li>
<li><span class="stability_0"><a href="#utilisbufferobject"><code>util.isBuffer(object)</code></a></span></li>
<li><span class="stability_0"><a href="#utilisdateobject"><code>util.isDate(object)</code></a></span></li>
<li><span class="stability_0"><a href="#utiliserrorobject"><code>util.isError(object)</code></a></span></li>
<li><span class="stability_0"><a href="#utilisfunctionobject"><code>util.isFunction(object)</code></a></span></li>
<li><span class="stability_0"><a href="#utilisnullobject"><code>util.isNull(object)</code></a></span></li>
<li><span class="stability_0"><a href="#utilisnullorundefinedobject"><code>util.isNullOrUndefined(object)</code></a></span></li>
<li><span class="stability_0"><a href="#utilisnumberobject"><code>util.isNumber(object)</code></a></span></li>
<li><span class="stability_0"><a href="#utilisobjectobject"><code>util.isObject(object)</code></a></span></li>
<li><span class="stability_0"><a href="#utilisprimitiveobject"><code>util.isPrimitive(object)</code></a></span></li>
<li><span class="stability_0"><a href="#utilisregexpobject"><code>util.isRegExp(object)</code></a></span></li>
<li><span class="stability_0"><a href="#utilisstringobject"><code>util.isString(object)</code></a></span></li>
<li><span class="stability_0"><a href="#utilissymbolobject"><code>util.isSymbol(object)</code></a></span></li>
<li><span class="stability_0"><a href="#utilisundefinedobject"><code>util.isUndefined(object)</code></a></span></li>
<li><span class="stability_0"><a href="#utillogstring"><code>util.log(string)</code></a></span></li>
</ul>
</li>
</ul>
</li>
</ul></div></div>
</li>
<li class="picker-header">
<a href="#">
<span class="picker-arrow"></span>
Index
</a>
<div class="picker"><ul>
<li><a href="documentation.html" class="nav-documentation">About this documentation</a></li>
<li><a href="synopsis.html" class="nav-synopsis">Usage and example</a></li>
<li>
<a href="index.html">Index</a>
</li>
</ul>
<hr class="line">
<ul>
<li><a href="assert.html" class="nav-assert">Assertion testing</a></li>
<li><a href="async_context.html" class="nav-async_context">Asynchronous context tracking</a></li>
<li><a href="async_hooks.html" class="nav-async_hooks">Async hooks</a></li>
<li><a href="buffer.html" class="nav-buffer">Buffer</a></li>
<li><a href="addons.html" class="nav-addons">C++ addons</a></li>
<li><a href="n-api.html" class="nav-n-api">C/C++ addons with Node-API</a></li>
<li><a href="embedding.html" class="nav-embedding">C++ embedder API</a></li>
<li><a href="child_process.html" class="nav-child_process">Child processes</a></li>
<li><a href="cluster.html" class="nav-cluster">Cluster</a></li>
<li><a href="cli.html" class="nav-cli">Command-line options</a></li>
<li><a href="console.html" class="nav-console">Console</a></li>
<li><a href="corepack.html" class="nav-corepack">Corepack</a></li>
<li><a href="crypto.html" class="nav-crypto">Crypto</a></li>
<li><a href="debugger.html" class="nav-debugger">Debugger</a></li>
<li><a href="deprecations.html" class="nav-deprecations">Deprecated APIs</a></li>
<li><a href="diagnostics_channel.html" class="nav-diagnostics_channel">Diagnostics Channel</a></li>
<li><a href="dns.html" class="nav-dns">DNS</a></li>
<li><a href="domain.html" class="nav-domain">Domain</a></li>
<li><a href="errors.html" class="nav-errors">Errors</a></li>
<li><a href="events.html" class="nav-events">Events</a></li>
<li><a href="fs.html" class="nav-fs">File system</a></li>
<li><a href="globals.html" class="nav-globals">Globals</a></li>
<li><a href="http.html" class="nav-http">HTTP</a></li>
<li><a href="http2.html" class="nav-http2">HTTP/2</a></li>
<li><a href="https.html" class="nav-https">HTTPS</a></li>
<li><a href="inspector.html" class="nav-inspector">Inspector</a></li>
<li><a href="intl.html" class="nav-intl">Internationalization</a></li>
<li><a href="modules.html" class="nav-modules">Modules: CommonJS modules</a></li>
<li><a href="esm.html" class="nav-esm">Modules: ECMAScript modules</a></li>
<li><a href="module.html" class="nav-module">Modules: <code>node:module</code> API</a></li>
<li><a href="packages.html" class="nav-packages">Modules: Packages</a></li>
<li><a href="net.html" class="nav-net">Net</a></li>
<li><a href="os.html" class="nav-os">OS</a></li>
<li><a href="path.html" class="nav-path">Path</a></li>
<li><a href="perf_hooks.html" class="nav-perf_hooks">Performance hooks</a></li>
<li><a href="permissions.html" class="nav-permissions">Permissions</a></li>
<li><a href="process.html" class="nav-process">Process</a></li>
<li><a href="punycode.html" class="nav-punycode">Punycode</a></li>
<li><a href="querystring.html" class="nav-querystring">Query strings</a></li>
<li><a href="readline.html" class="nav-readline">Readline</a></li>
<li><a href="repl.html" class="nav-repl">REPL</a></li>
<li><a href="report.html" class="nav-report">Report</a></li>
<li><a href="single-executable-applications.html" class="nav-single-executable-applications">Single executable applications</a></li>
<li><a href="stream.html" class="nav-stream">Stream</a></li>
<li><a href="string_decoder.html" class="nav-string_decoder">String decoder</a></li>
<li><a href="test.html" class="nav-test">Test runner</a></li>
<li><a href="timers.html" class="nav-timers">Timers</a></li>
<li><a href="tls.html" class="nav-tls">TLS/SSL</a></li>
<li><a href="tracing.html" class="nav-tracing">Trace events</a></li>
<li><a href="tty.html" class="nav-tty">TTY</a></li>
<li><a href="dgram.html" class="nav-dgram">UDP/datagram</a></li>
<li><a href="url.html" class="nav-url">URL</a></li>
<li><a href="util.html" class="nav-util active">Utilities</a></li>
<li><a href="v8.html" class="nav-v8">V8</a></li>
<li><a href="vm.html" class="nav-vm">VM</a></li>
<li><a href="wasi.html" class="nav-wasi">WASI</a></li>
<li><a href="webcrypto.html" class="nav-webcrypto">Web Crypto API</a></li>
<li><a href="webstreams.html" class="nav-webstreams">Web Streams API</a></li>
<li><a href="worker_threads.html" class="nav-worker_threads">Worker threads</a></li>
<li><a href="zlib.html" class="nav-zlib">Zlib</a></li>
</ul>
<hr class="line">
<ul>
<li><a href="https://github.com/nodejs/node" class="nav-https-github-com-nodejs-node">Code repository and issue tracker</a></li>
</ul></div>
</li>
<li class="picker-header">
<a href="#">
<span class="picker-arrow"></span>
Other versions
</a>
<div class="picker"><ol id="alt-docs"><li><a href="https://nodejs.org/docs/latest-v22.x/api/util.html">22.x</a></li>
<li><a href="https://nodejs.org/docs/latest-v21.x/api/util.html">21.x</a></li>
<li><a href="https://nodejs.org/docs/latest-v20.x/api/util.html">20.x <b>LTS</b></a></li>
<li><a href="https://nodejs.org/docs/latest-v19.x/api/util.html">19.x</a></li>
<li><a href="https://nodejs.org/docs/latest-v18.x/api/util.html">18.x <b>LTS</b></a></li>
<li><a href="https://nodejs.org/docs/latest-v17.x/api/util.html">17.x</a></li>
<li><a href="https://nodejs.org/docs/latest-v16.x/api/util.html">16.x</a></li>
<li><a href="https://nodejs.org/docs/latest-v15.x/api/util.html">15.x</a></li>
<li><a href="https://nodejs.org/docs/latest-v14.x/api/util.html">14.x</a></li>
<li><a href="https://nodejs.org/docs/latest-v13.x/api/util.html">13.x</a></li>
<li><a href="https://nodejs.org/docs/latest-v12.x/api/util.html">12.x</a></li>
<li><a href="https://nodejs.org/docs/latest-v11.x/api/util.html">11.x</a></li>
<li><a href="https://nodejs.org/docs/latest-v10.x/api/util.html">10.x</a></li>
<li><a href="https://nodejs.org/docs/latest-v9.x/api/util.html">9.x</a></li>
<li><a href="https://nodejs.org/docs/latest-v8.x/api/util.html">8.x</a></li>
<li><a href="https://nodejs.org/docs/latest-v7.x/api/util.html">7.x</a></li>
<li><a href="https://nodejs.org/docs/latest-v6.x/api/util.html">6.x</a></li>
<li><a href="https://nodejs.org/docs/latest-v5.x/api/util.html">5.x</a></li>
<li><a href="https://nodejs.org/docs/latest-v4.x/api/util.html">4.x</a></li>
<li><a href="https://nodejs.org/docs/latest-v0.12.x/api/util.html">0.12.x</a></li>
<li><a href="https://nodejs.org/docs/latest-v0.10.x/api/util.html">0.10.x</a></li></ol></div>
</li>
<li class="picker-header">
<a href="#">
<span class="picker-arrow"></span>
Options
</a>
<div class="picker">
<ul>
<li>
<a href="all.html">View on single page</a>
</li>
<li>
<a href="util.json">View as JSON</a>
</li>
<li class="edit_on_github"><a href="https://github.com/nodejs/node/edit/main/doc/api/util.md">Edit on GitHub</a></li>
</ul>
</div>
</li>
</ul>
</div>
<hr>
</header>
<details role="navigation" id="toc" open><summary>Table of contents</summary><ul>
<li><span class="stability_2"><a href="#util">Util</a></span>
<ul>
<li><a href="#utilcallbackifyoriginal"><code>util.callbackify(original)</code></a></li>
<li><a href="#utildebuglogsection-callback"><code>util.debuglog(section[, callback])</code></a>
<ul>
<li><a href="#debuglogenabled"><code>debuglog().enabled</code></a></li>
</ul>
</li>
<li><a href="#utildebugsection"><code>util.debug(section)</code></a></li>
<li><a href="#utildeprecatefn-msg-code"><code>util.deprecate(fn, msg[, code])</code></a></li>
<li><a href="#utilformatformat-args"><code>util.format(format[, ...args])</code></a></li>
<li><a href="#utilformatwithoptionsinspectoptions-format-args"><code>util.formatWithOptions(inspectOptions, format[, ...args])</code></a></li>
<li><a href="#utilgetsystemerrornameerr"><code>util.getSystemErrorName(err)</code></a></li>
<li><a href="#utilgetsystemerrormap"><code>util.getSystemErrorMap()</code></a></li>
<li><span class="stability_3"><a href="#utilinheritsconstructor-superconstructor"><code>util.inherits(constructor, superConstructor)</code></a></span></li>
<li><a href="#utilinspectobject-options"><code>util.inspect(object[, options])</code></a></li>
<li><a href="#utilinspectobject-showhidden-depth-colors"><code>util.inspect(object[, showHidden[, depth[, colors]]])</code></a>
<ul>
<li><a href="#customizing-utilinspect-colors">Customizing <code>util.inspect</code> colors</a>
<ul>
<li><a href="#modifiers">Modifiers</a></li>
<li><a href="#foreground-colors">Foreground colors</a></li>
<li><a href="#background-colors">Background colors</a></li>
</ul>
</li>
<li><a href="#custom-inspection-functions-on-objects">Custom inspection functions on objects</a></li>
<li><a href="#utilinspectcustom"><code>util.inspect.custom</code></a></li>
<li><a href="#utilinspectdefaultoptions"><code>util.inspect.defaultOptions</code></a></li>
</ul>
</li>
<li><a href="#utilisdeepstrictequalval1-val2"><code>util.isDeepStrictEqual(val1, val2)</code></a></li>
<li><span class="stability_1"><a href="#class-utilmimetype">Class: <code>util.MIMEType</code></a></span>
<ul>
<li><a href="#constructor-new-mimetypeinput">Constructor: <code>new MIMEType(input)</code></a></li>
<li><a href="#mimetype"><code>mime.type</code></a></li>
<li><a href="#mimesubtype"><code>mime.subtype</code></a></li>
<li><a href="#mimeessence"><code>mime.essence</code></a></li>
<li><a href="#mimeparams"><code>mime.params</code></a></li>
<li><a href="#mimetostring"><code>mime.toString()</code></a></li>
<li><a href="#mimetojson"><code>mime.toJSON()</code></a></li>
</ul>
</li>
<li><a href="#class-utilmimeparams">Class: <code>util.MIMEParams</code></a>
<ul>
<li><a href="#constructor-new-mimeparams">Constructor: <code>new MIMEParams()</code></a></li>
<li><a href="#mimeparamsdeletename"><code>mimeParams.delete(name)</code></a></li>
<li><a href="#mimeparamsentries"><code>mimeParams.entries()</code></a></li>
<li><a href="#mimeparamsgetname"><code>mimeParams.get(name)</code></a></li>
<li><a href="#mimeparamshasname"><code>mimeParams.has(name)</code></a></li>
<li><a href="#mimeparamskeys"><code>mimeParams.keys()</code></a></li>
<li><a href="#mimeparamssetname-value"><code>mimeParams.set(name, value)</code></a></li>
<li><a href="#mimeparamsvalues"><code>mimeParams.values()</code></a></li>
<li><a href="#mimeparamsiterator"><code>mimeParams[@@iterator]()</code></a></li>
</ul>
</li>
<li><a href="#utilparseargsconfig"><code>util.parseArgs([config])</code></a>
<ul>
<li><a href="#parseargs-tokens"><code>parseArgs</code> <code>tokens</code></a></li>
</ul>
</li>
<li><span class="stability_1"><a href="#utilparseenvcontent"><code>util.parseEnv(content)</code></a></span></li>
<li><a href="#utilpromisifyoriginal"><code>util.promisify(original)</code></a>
<ul>
<li><a href="#custom-promisified-functions">Custom promisified functions</a></li>
<li><a href="#utilpromisifycustom"><code>util.promisify.custom</code></a></li>
</ul>
</li>
<li><a href="#utilstripvtcontrolcharactersstr"><code>util.stripVTControlCharacters(str)</code></a></li>
<li><span class="stability_1"><a href="#utilstyletextformat-text"><code>util.styleText(format, text)</code></a></span></li>
<li><a href="#class-utiltextdecoder">Class: <code>util.TextDecoder</code></a>
<ul>
<li><a href="#whatwg-supported-encodings">WHATWG supported encodings</a>
<ul>
<li><a href="#encodings-supported-by-default-with-full-icu-data">Encodings supported by default (with full ICU data)</a></li>
<li><a href="#encodings-supported-when-nodejs-is-built-with-the-small-icu-option">Encodings supported when Node.js is built with the <code>small-icu</code> option</a></li>
<li><a href="#encodings-supported-when-icu-is-disabled">Encodings supported when ICU is disabled</a></li>
</ul>
</li>
<li><a href="#new-textdecoderencoding-options"><code>new TextDecoder([encoding[, options]])</code></a></li>
<li><a href="#textdecoderdecodeinput-options"><code>textDecoder.decode([input[, options]])</code></a></li>
<li><a href="#textdecoderencoding"><code>textDecoder.encoding</code></a></li>
<li><a href="#textdecoderfatal"><code>textDecoder.fatal</code></a></li>
<li><a href="#textdecoderignorebom"><code>textDecoder.ignoreBOM</code></a></li>
</ul>
</li>
<li><a href="#class-utiltextencoder">Class: <code>util.TextEncoder</code></a>
<ul>
<li><a href="#textencoderencodeinput"><code>textEncoder.encode([input])</code></a></li>
<li><a href="#textencoderencodeintosrc-dest"><code>textEncoder.encodeInto(src, dest)</code></a></li>
<li><a href="#textencoderencoding"><code>textEncoder.encoding</code></a></li>
</ul>
</li>
<li><a href="#utiltousvstringstring"><code>util.toUSVString(string)</code></a></li>
<li><span class="stability_1"><a href="#utiltransferableabortcontroller"><code>util.transferableAbortController()</code></a></span></li>
<li><span class="stability_1"><a href="#utiltransferableabortsignalsignal"><code>util.transferableAbortSignal(signal)</code></a></span></li>
<li><span class="stability_1"><a href="#utilabortedsignal-resource"><code>util.aborted(signal, resource)</code></a></span></li>
<li><a href="#utiltypes"><code>util.types</code></a>
<ul>
<li><a href="#utiltypesisanyarraybuffervalue"><code>util.types.isAnyArrayBuffer(value)</code></a></li>
<li><a href="#utiltypesisarraybufferviewvalue"><code>util.types.isArrayBufferView(value)</code></a></li>
<li><a href="#utiltypesisargumentsobjectvalue"><code>util.types.isArgumentsObject(value)</code></a></li>
<li><a href="#utiltypesisarraybuffervalue"><code>util.types.isArrayBuffer(value)</code></a></li>
<li><a href="#utiltypesisasyncfunctionvalue"><code>util.types.isAsyncFunction(value)</code></a></li>
<li><a href="#utiltypesisbigint64arrayvalue"><code>util.types.isBigInt64Array(value)</code></a></li>
<li><a href="#utiltypesisbiguint64arrayvalue"><code>util.types.isBigUint64Array(value)</code></a></li>
<li><a href="#utiltypesisbooleanobjectvalue"><code>util.types.isBooleanObject(value)</code></a></li>
<li><a href="#utiltypesisboxedprimitivevalue"><code>util.types.isBoxedPrimitive(value)</code></a></li>
<li><a href="#utiltypesiscryptokeyvalue"><code>util.types.isCryptoKey(value)</code></a></li>
<li><a href="#utiltypesisdataviewvalue"><code>util.types.isDataView(value)</code></a></li>
<li><a href="#utiltypesisdatevalue"><code>util.types.isDate(value)</code></a></li>
<li><a href="#utiltypesisexternalvalue"><code>util.types.isExternal(value)</code></a></li>
<li><a href="#utiltypesisfloat32arrayvalue"><code>util.types.isFloat32Array(value)</code></a></li>
<li><a href="#utiltypesisfloat64arrayvalue"><code>util.types.isFloat64Array(value)</code></a></li>
<li><a href="#utiltypesisgeneratorfunctionvalue"><code>util.types.isGeneratorFunction(value)</code></a></li>
<li><a href="#utiltypesisgeneratorobjectvalue"><code>util.types.isGeneratorObject(value)</code></a></li>
<li><a href="#utiltypesisint8arrayvalue"><code>util.types.isInt8Array(value)</code></a></li>
<li><a href="#utiltypesisint16arrayvalue"><code>util.types.isInt16Array(value)</code></a></li>
<li><a href="#utiltypesisint32arrayvalue"><code>util.types.isInt32Array(value)</code></a></li>
<li><a href="#utiltypesiskeyobjectvalue"><code>util.types.isKeyObject(value)</code></a></li>
<li><a href="#utiltypesismapvalue"><code>util.types.isMap(value)</code></a></li>
<li><a href="#utiltypesismapiteratorvalue"><code>util.types.isMapIterator(value)</code></a></li>
<li><a href="#utiltypesismodulenamespaceobjectvalue"><code>util.types.isModuleNamespaceObject(value)</code></a></li>
<li><a href="#utiltypesisnativeerrorvalue"><code>util.types.isNativeError(value)</code></a></li>
<li><a href="#utiltypesisnumberobjectvalue"><code>util.types.isNumberObject(value)</code></a></li>
<li><a href="#utiltypesispromisevalue"><code>util.types.isPromise(value)</code></a></li>
<li><a href="#utiltypesisproxyvalue"><code>util.types.isProxy(value)</code></a></li>
<li><a href="#utiltypesisregexpvalue"><code>util.types.isRegExp(value)</code></a></li>
<li><a href="#utiltypesissetvalue"><code>util.types.isSet(value)</code></a></li>
<li><a href="#utiltypesissetiteratorvalue"><code>util.types.isSetIterator(value)</code></a></li>
<li><a href="#utiltypesissharedarraybuffervalue"><code>util.types.isSharedArrayBuffer(value)</code></a></li>
<li><a href="#utiltypesisstringobjectvalue"><code>util.types.isStringObject(value)</code></a></li>
<li><a href="#utiltypesissymbolobjectvalue"><code>util.types.isSymbolObject(value)</code></a></li>
<li><a href="#utiltypesistypedarrayvalue"><code>util.types.isTypedArray(value)</code></a></li>
<li><a href="#utiltypesisuint8arrayvalue"><code>util.types.isUint8Array(value)</code></a></li>
<li><a href="#utiltypesisuint8clampedarrayvalue"><code>util.types.isUint8ClampedArray(value)</code></a></li>
<li><a href="#utiltypesisuint16arrayvalue"><code>util.types.isUint16Array(value)</code></a></li>
<li><a href="#utiltypesisuint32arrayvalue"><code>util.types.isUint32Array(value)</code></a></li>
<li><a href="#utiltypesisweakmapvalue"><code>util.types.isWeakMap(value)</code></a></li>
<li><a href="#utiltypesisweaksetvalue"><code>util.types.isWeakSet(value)</code></a></li>
</ul>
</li>
<li><a href="#deprecated-apis">Deprecated APIs</a>
<ul>
<li><span class="stability_0"><a href="#util_extendtarget-source"><code>util._extend(target, source)</code></a></span></li>
<li><span class="stability_0"><a href="#utilisarrayobject"><code>util.isArray(object)</code></a></span></li>
<li><span class="stability_0"><a href="#utilisbooleanobject"><code>util.isBoolean(object)</code></a></span></li>
<li><span class="stability_0"><a href="#utilisbufferobject"><code>util.isBuffer(object)</code></a></span></li>
<li><span class="stability_0"><a href="#utilisdateobject"><code>util.isDate(object)</code></a></span></li>
<li><span class="stability_0"><a href="#utiliserrorobject"><code>util.isError(object)</code></a></span></li>
<li><span class="stability_0"><a href="#utilisfunctionobject"><code>util.isFunction(object)</code></a></span></li>
<li><span class="stability_0"><a href="#utilisnullobject"><code>util.isNull(object)</code></a></span></li>
<li><span class="stability_0"><a href="#utilisnullorundefinedobject"><code>util.isNullOrUndefined(object)</code></a></span></li>
<li><span class="stability_0"><a href="#utilisnumberobject"><code>util.isNumber(object)</code></a></span></li>
<li><span class="stability_0"><a href="#utilisobjectobject"><code>util.isObject(object)</code></a></span></li>
<li><span class="stability_0"><a href="#utilisprimitiveobject"><code>util.isPrimitive(object)</code></a></span></li>
<li><span class="stability_0"><a href="#utilisregexpobject"><code>util.isRegExp(object)</code></a></span></li>
<li><span class="stability_0"><a href="#utilisstringobject"><code>util.isString(object)</code></a></span></li>
<li><span class="stability_0"><a href="#utilissymbolobject"><code>util.isSymbol(object)</code></a></span></li>
<li><span class="stability_0"><a href="#utilisundefinedobject"><code>util.isUndefined(object)</code></a></span></li>
<li><span class="stability_0"><a href="#utillogstring"><code>util.log(string)</code></a></span></li>
</ul>
</li>
</ul>
</li>
</ul></details>
<div role="main" id="apicontent">
<h2>Util<span><a class="mark" href="#util" id="util">#</a></span><a aria-hidden="true" class="legacy" id="util_util"></a></h2>
<p></p><div class="api_stability api_stability_2"><a href="documentation.html#stability-index">Stability: 2</a> - Stable</div><p></p>
<p><strong>Source Code:</strong> <a href="https://github.com/nodejs/node/blob/v20.15.1/lib/util.js">lib/util.js</a></p>
<p>The <code>node:util</code> module supports the needs of Node.js internal APIs. Many of the
utilities are useful for application and module developers as well. To access
it:</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);</code> <button class="copy-button">copy</button></pre>
<section><h3><code>util.callbackify(original)</code><span><a class="mark" href="#utilcallbackifyoriginal" id="utilcallbackifyoriginal">#</a></span><a aria-hidden="true" class="legacy" id="util_util_callbackify_original"></a></h3>
<div class="api_metadata">
<span>Added in: v8.2.0</span>
</div>
<ul>
<li><code>original</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> An <code>async</code> function</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> a callback style function</li>
</ul>
<p>Takes an <code>async</code> function (or a function that returns a <code>Promise</code>) and returns a
function following the error-first callback style, i.e. taking
an <code>(err, value) => ...</code> callback as the last argument. In the callback, the
first argument will be the rejection reason (or <code>null</code> if the <code>Promise</code>
resolved), and the second argument will be the resolved value.</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);
<span class="hljs-keyword">async</span> <span class="hljs-keyword">function</span> <span class="hljs-title function_">fn</span>(<span class="hljs-params"></span>) {
<span class="hljs-keyword">return</span> <span class="hljs-string">'hello world'</span>;
}
<span class="hljs-keyword">const</span> callbackFunction = util.<span class="hljs-title function_">callbackify</span>(fn);
<span class="hljs-title function_">callbackFunction</span>(<span class="hljs-function">(<span class="hljs-params">err, ret</span>) =></span> {
<span class="hljs-keyword">if</span> (err) <span class="hljs-keyword">throw</span> err;
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(ret);
});</code> <button class="copy-button">copy</button></pre>
<p>Will print:</p>
<pre><code class="language-text">hello world</code> <button class="copy-button">copy</button></pre>
<p>The callback is executed asynchronously, and will have a limited stack trace.
If the callback throws, the process will emit an <a href="process.html#event-uncaughtexception"><code>'uncaughtException'</code></a>
event, and if not handled will exit.</p>
<p>Since <code>null</code> has a special meaning as the first argument to a callback, if a
wrapped function rejects a <code>Promise</code> with a falsy value as a reason, the value
is wrapped in an <code>Error</code> with the original value stored in a field named
<code>reason</code>.</p>
<pre><code class="language-js"><span class="hljs-keyword">function</span> <span class="hljs-title function_">fn</span>(<span class="hljs-params"></span>) {
<span class="hljs-keyword">return</span> <span class="hljs-title class_">Promise</span>.<span class="hljs-title function_">reject</span>(<span class="hljs-literal">null</span>);
}
<span class="hljs-keyword">const</span> callbackFunction = util.<span class="hljs-title function_">callbackify</span>(fn);
<span class="hljs-title function_">callbackFunction</span>(<span class="hljs-function">(<span class="hljs-params">err, ret</span>) =></span> {
<span class="hljs-comment">// When the Promise was rejected with `null` it is wrapped with an Error and</span>
<span class="hljs-comment">// the original value is stored in `reason`.</span>
err && <span class="hljs-title class_">Object</span>.<span class="hljs-title function_">hasOwn</span>(err, <span class="hljs-string">'reason'</span>) && err.<span class="hljs-property">reason</span> === <span class="hljs-literal">null</span>; <span class="hljs-comment">// true</span>
});</code> <button class="copy-button">copy</button></pre>
</section><section><h3><code>util.debuglog(section[, callback])</code><span><a class="mark" href="#utildebuglogsection-callback" id="utildebuglogsection-callback">#</a></span><a aria-hidden="true" class="legacy" id="util_util_debuglog_section_callback"></a></h3>
<div class="api_metadata">
<span>Added in: v0.11.3</span>
</div>
<ul>
<li><code>section</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> A string identifying the portion of the application for
which the <code>debuglog</code> function is being created.</li>
<li><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> A callback invoked the first time the logging function
is called with a function argument that is a more optimized logging function.</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> The logging function</li>
</ul>
<p>The <code>util.debuglog()</code> method is used to create a function that conditionally
writes debug messages to <code>stderr</code> based on the existence of the <code>NODE_DEBUG</code>
environment variable. If the <code>section</code> name appears within the value of that
environment variable, then the returned function operates similar to
<a href="console.html#consoleerrordata-args"><code>console.error()</code></a>. If not, then the returned function is a no-op.</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);
<span class="hljs-keyword">const</span> debuglog = util.<span class="hljs-title function_">debuglog</span>(<span class="hljs-string">'foo'</span>);
<span class="hljs-title function_">debuglog</span>(<span class="hljs-string">'hello from foo [%d]'</span>, <span class="hljs-number">123</span>);</code> <button class="copy-button">copy</button></pre>
<p>If this program is run with <code>NODE_DEBUG=foo</code> in the environment, then
it will output something like:</p>
<pre><code class="language-console">FOO 3245: hello from foo [123]</code> <button class="copy-button">copy</button></pre>
<p>where <code>3245</code> is the process id. If it is not run with that
environment variable set, then it will not print anything.</p>
<p>The <code>section</code> supports wildcard also:</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);
<span class="hljs-keyword">const</span> debuglog = util.<span class="hljs-title function_">debuglog</span>(<span class="hljs-string">'foo-bar'</span>);
<span class="hljs-title function_">debuglog</span>(<span class="hljs-string">'hi there, it\'s foo-bar [%d]'</span>, <span class="hljs-number">2333</span>);</code> <button class="copy-button">copy</button></pre>
<p>if it is run with <code>NODE_DEBUG=foo*</code> in the environment, then it will output
something like:</p>
<pre><code class="language-console">FOO-BAR 3257: hi there, it's foo-bar [2333]</code> <button class="copy-button">copy</button></pre>
<p>Multiple comma-separated <code>section</code> names may be specified in the <code>NODE_DEBUG</code>
environment variable: <code>NODE_DEBUG=fs,net,tls</code>.</p>
<p>The optional <code>callback</code> argument can be used to replace the logging function
with a different function that doesn't have any initialization or
unnecessary wrapping.</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);
<span class="hljs-keyword">let</span> debuglog = util.<span class="hljs-title function_">debuglog</span>(<span class="hljs-string">'internals'</span>, <span class="hljs-function">(<span class="hljs-params">debug</span>) =></span> {
<span class="hljs-comment">// Replace with a logging function that optimizes out</span>
<span class="hljs-comment">// testing if the section is enabled</span>
debuglog = debug;
});</code> <button class="copy-button">copy</button></pre>
<h4><code>debuglog().enabled</code><span><a class="mark" href="#debuglogenabled" id="debuglogenabled">#</a></span><a aria-hidden="true" class="legacy" id="util_debuglog_enabled"></a></h4>
<div class="api_metadata">
<span>Added in: v14.9.0</span>
</div>
<ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>The <code>util.debuglog().enabled</code> getter is used to create a test that can be used
in conditionals based on the existence of the <code>NODE_DEBUG</code> environment variable.
If the <code>section</code> name appears within the value of that environment variable,
then the returned value will be <code>true</code>. If not, then the returned value will be
<code>false</code>.</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);
<span class="hljs-keyword">const</span> enabled = util.<span class="hljs-title function_">debuglog</span>(<span class="hljs-string">'foo'</span>).<span class="hljs-property">enabled</span>;
<span class="hljs-keyword">if</span> (enabled) {
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">'hello from foo [%d]'</span>, <span class="hljs-number">123</span>);
}</code> <button class="copy-button">copy</button></pre>
<p>If this program is run with <code>NODE_DEBUG=foo</code> in the environment, then it will
output something like:</p>
<pre><code class="language-console">hello from foo [123]</code> <button class="copy-button">copy</button></pre>
</section><section><h3><code>util.debug(section)</code><span><a class="mark" href="#utildebugsection" id="utildebugsection">#</a></span><a aria-hidden="true" class="legacy" id="util_util_debug_section"></a></h3>
<div class="api_metadata">
<span>Added in: v14.9.0</span>
</div>
<p>Alias for <code>util.debuglog</code>. Usage allows for readability of that doesn't imply
logging when only using <code>util.debuglog().enabled</code>.</p>
</section><section><h3><code>util.deprecate(fn, msg[, code])</code><span><a class="mark" href="#utildeprecatefn-msg-code" id="utildeprecatefn-msg-code">#</a></span><a aria-hidden="true" class="legacy" id="util_util_deprecate_fn_msg_code"></a></h3>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v10.0.0</td>
<td><p>Deprecation warnings are only emitted once for each code.</p></td></tr>
<tr><td>v0.8.0</td>
<td><p><span>Added in: v0.8.0</span></p></td></tr>
</tbody></table>
</details>
</div>
<ul>
<li><code>fn</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> The function that is being deprecated.</li>
<li><code>msg</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> A warning message to display when the deprecated function is
invoked.</li>
<li><code>code</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> A deprecation code. See the <a href="deprecations.html#list-of-deprecated-apis">list of deprecated APIs</a> for a
list of codes.</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> The deprecated function wrapped to emit a warning.</li>
</ul>
<p>The <code>util.deprecate()</code> method wraps <code>fn</code> (which may be a function or class) in
such a way that it is marked as deprecated.</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);
<span class="hljs-built_in">exports</span>.<span class="hljs-property">obsoleteFunction</span> = util.<span class="hljs-title function_">deprecate</span>(<span class="hljs-function">() =></span> {
<span class="hljs-comment">// Do something here.</span>
}, <span class="hljs-string">'obsoleteFunction() is deprecated. Use newShinyFunction() instead.'</span>);</code> <button class="copy-button">copy</button></pre>
<p>When called, <code>util.deprecate()</code> will return a function that will emit a
<code>DeprecationWarning</code> using the <a href="process.html#event-warning"><code>'warning'</code></a> event. The warning will
be emitted and printed to <code>stderr</code> the first time the returned function is
called. After the warning is emitted, the wrapped function is called without
emitting a warning.</p>
<p>If the same optional <code>code</code> is supplied in multiple calls to <code>util.deprecate()</code>,
the warning will be emitted only once for that <code>code</code>.</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);
<span class="hljs-keyword">const</span> fn1 = util.<span class="hljs-title function_">deprecate</span>(someFunction, someMessage, <span class="hljs-string">'DEP0001'</span>);
<span class="hljs-keyword">const</span> fn2 = util.<span class="hljs-title function_">deprecate</span>(someOtherFunction, someOtherMessage, <span class="hljs-string">'DEP0001'</span>);
<span class="hljs-title function_">fn1</span>(); <span class="hljs-comment">// Emits a deprecation warning with code DEP0001</span>
<span class="hljs-title function_">fn2</span>(); <span class="hljs-comment">// Does not emit a deprecation warning because it has the same code</span></code> <button class="copy-button">copy</button></pre>
<p>If either the <code>--no-deprecation</code> or <code>--no-warnings</code> command-line flags are
used, or if the <code>process.noDeprecation</code> property is set to <code>true</code> <em>prior</em> to
the first deprecation warning, the <code>util.deprecate()</code> method does nothing.</p>
<p>If the <code>--trace-deprecation</code> or <code>--trace-warnings</code> command-line flags are set,
or the <code>process.traceDeprecation</code> property is set to <code>true</code>, a warning and a
stack trace are printed to <code>stderr</code> the first time the deprecated function is
called.</p>
<p>If the <code>--throw-deprecation</code> command-line flag is set, or the
<code>process.throwDeprecation</code> property is set to <code>true</code>, then an exception will be
thrown when the deprecated function is called.</p>
<p>The <code>--throw-deprecation</code> command-line flag and <code>process.throwDeprecation</code>
property take precedence over <code>--trace-deprecation</code> and
<code>process.traceDeprecation</code>.</p>
</section><section><h3><code>util.format(format[, ...args])</code><span><a class="mark" href="#utilformatformat-args" id="utilformatformat-args">#</a></span><a aria-hidden="true" class="legacy" id="util_util_format_format_args"></a></h3>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v12.11.0</td>
<td><p>The <code>%c</code> specifier is ignored now.</p></td></tr>
<tr><td>v12.0.0</td>
<td><p>The <code>format</code> argument is now only taken as such if it actually contains format specifiers.</p></td></tr>
<tr><td>v12.0.0</td>
<td><p>If the <code>format</code> argument is not a format string, the output string's formatting is no longer dependent on the type of the first argument. This change removes previously present quotes from strings that were being output when the first argument was not a string.</p></td></tr>
<tr><td>v11.4.0</td>
<td><p>The <code>%d</code>, <code>%f</code>, and <code>%i</code> specifiers now support Symbols properly.</p></td></tr>
<tr><td>v11.4.0</td>
<td><p>The <code>%o</code> specifier's <code>depth</code> has default depth of 4 again.</p></td></tr>
<tr><td>v11.0.0</td>
<td><p>The <code>%o</code> specifier's <code>depth</code> option will now fall back to the default depth.</p></td></tr>
<tr><td>v10.12.0</td>
<td><p>The <code>%d</code> and <code>%i</code> specifiers now support BigInt.</p></td></tr>
<tr><td>v8.4.0</td>
<td><p>The <code>%o</code> and <code>%O</code> specifiers are supported now.</p></td></tr>
<tr><td>v0.5.3</td>
<td><p><span>Added in: v0.5.3</span></p></td></tr>
</tbody></table>
</details>
</div>
<ul>
<li><code>format</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> A <code>printf</code>-like format string.</li>
</ul>
<p>The <code>util.format()</code> method returns a formatted string using the first argument
as a <code>printf</code>-like format string which can contain zero or more format
specifiers. Each specifier is replaced with the converted value from the
corresponding argument. Supported specifiers are:</p>
<ul>
<li><code>%s</code>: <code>String</code> will be used to convert all values except <code>BigInt</code>, <code>Object</code>
and <code>-0</code>. <code>BigInt</code> values will be represented with an <code>n</code> and Objects that
have no user defined <code>toString</code> function are inspected using <code>util.inspect()</code>
with options <code>{ depth: 0, colors: false, compact: 3 }</code>.</li>
<li><code>%d</code>: <code>Number</code> will be used to convert all values except <code>BigInt</code> and
<code>Symbol</code>.</li>
<li><code>%i</code>: <code>parseInt(value, 10)</code> is used for all values except <code>BigInt</code> and
<code>Symbol</code>.</li>
<li><code>%f</code>: <code>parseFloat(value)</code> is used for all values expect <code>Symbol</code>.</li>
<li><code>%j</code>: JSON. Replaced with the string <code>'[Circular]'</code> if the argument contains
circular references.</li>
<li><code>%o</code>: <code>Object</code>. A string representation of an object with generic JavaScript
object formatting. Similar to <code>util.inspect()</code> with options
<code>{ showHidden: true, showProxy: true }</code>. This will show the full object
including non-enumerable properties and proxies.</li>
<li><code>%O</code>: <code>Object</code>. A string representation of an object with generic JavaScript
object formatting. Similar to <code>util.inspect()</code> without options. This will show
the full object not including non-enumerable properties and proxies.</li>
<li><code>%c</code>: <code>CSS</code>. This specifier is ignored and will skip any CSS passed in.</li>
<li><code>%%</code>: single percent sign (<code>'%'</code>). This does not consume an argument.</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> The formatted string</li>
</ul>
<p>If a specifier does not have a corresponding argument, it is not replaced:</p>
<pre><code class="language-js">util.<span class="hljs-title function_">format</span>(<span class="hljs-string">'%s:%s'</span>, <span class="hljs-string">'foo'</span>);
<span class="hljs-comment">// Returns: 'foo:%s'</span></code> <button class="copy-button">copy</button></pre>
<p>Values that are not part of the format string are formatted using
<code>util.inspect()</code> if their type is not <code>string</code>.</p>
<p>If there are more arguments passed to the <code>util.format()</code> method than the
number of specifiers, the extra arguments are concatenated to the returned
string, separated by spaces:</p>
<pre><code class="language-js">util.<span class="hljs-title function_">format</span>(<span class="hljs-string">'%s:%s'</span>, <span class="hljs-string">'foo'</span>, <span class="hljs-string">'bar'</span>, <span class="hljs-string">'baz'</span>);
<span class="hljs-comment">// Returns: 'foo:bar baz'</span></code> <button class="copy-button">copy</button></pre>
<p>If the first argument does not contain a valid format specifier, <code>util.format()</code>
returns a string that is the concatenation of all arguments separated by spaces:</p>
<pre><code class="language-js">util.<span class="hljs-title function_">format</span>(<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, <span class="hljs-number">3</span>);
<span class="hljs-comment">// Returns: '1 2 3'</span></code> <button class="copy-button">copy</button></pre>
<p>If only one argument is passed to <code>util.format()</code>, it is returned as it is
without any formatting:</p>
<pre><code class="language-js">util.<span class="hljs-title function_">format</span>(<span class="hljs-string">'%% %s'</span>);
<span class="hljs-comment">// Returns: '%% %s'</span></code> <button class="copy-button">copy</button></pre>
<p><code>util.format()</code> is a synchronous method that is intended as a debugging tool.
Some input values can have a significant performance overhead that can block the
event loop. Use this function with care and never in a hot code path.</p>
</section><section><h3><code>util.formatWithOptions(inspectOptions, format[, ...args])</code><span><a class="mark" href="#utilformatwithoptionsinspectoptions-format-args" id="utilformatwithoptionsinspectoptions-format-args">#</a></span><a aria-hidden="true" class="legacy" id="util_util_formatwithoptions_inspectoptions_format_args"></a></h3>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>inspectOptions</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li>
<li><code>format</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li>
</ul>
<p>This function is identical to <a href="#utilformatformat-args"><code>util.format()</code></a>, except in that it takes
an <code>inspectOptions</code> argument which specifies options that are passed along to
<a href="#utilinspectobject-options"><code>util.inspect()</code></a>.</p>
<pre><code class="language-js">util.<span class="hljs-title function_">formatWithOptions</span>({ <span class="hljs-attr">colors</span>: <span class="hljs-literal">true</span> }, <span class="hljs-string">'See object %O'</span>, { <span class="hljs-attr">foo</span>: <span class="hljs-number">42</span> });
<span class="hljs-comment">// Returns 'See object { foo: 42 }', where `42` is colored as a number</span>
<span class="hljs-comment">// when printed to a terminal.</span></code> <button class="copy-button">copy</button></pre>
</section><section><h3><code>util.getSystemErrorName(err)</code><span><a class="mark" href="#utilgetsystemerrornameerr" id="utilgetsystemerrornameerr">#</a></span><a aria-hidden="true" class="legacy" id="util_util_getsystemerrorname_err"></a></h3>
<div class="api_metadata">
<span>Added in: v9.7.0</span>
</div>
<ul>
<li><code>err</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li>
</ul>
<p>Returns the string name for a numeric error code that comes from a Node.js API.
The mapping between error codes and error names is platform-dependent.
See <a href="errors.html#common-system-errors">Common System Errors</a> for the names of common errors.</p>
<pre><code class="language-js">fs.<span class="hljs-title function_">access</span>(<span class="hljs-string">'file/that/does/not/exist'</span>, <span class="hljs-function">(<span class="hljs-params">err</span>) =></span> {
<span class="hljs-keyword">const</span> name = util.<span class="hljs-title function_">getSystemErrorName</span>(err.<span class="hljs-property">errno</span>);
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">error</span>(name); <span class="hljs-comment">// ENOENT</span>
});</code> <button class="copy-button">copy</button></pre>
</section><section><h3><code>util.getSystemErrorMap()</code><span><a class="mark" href="#utilgetsystemerrormap" id="utilgetsystemerrormap">#</a></span><a aria-hidden="true" class="legacy" id="util_util_getsystemerrormap"></a></h3>
<div class="api_metadata">
<span>Added in: v16.0.0, v14.17.0</span>
</div>
<ul>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map" class="type"><Map></a></li>
</ul>
<p>Returns a Map of all system error codes available from the Node.js API.
The mapping between error codes and error names is platform-dependent.
See <a href="errors.html#common-system-errors">Common System Errors</a> for the names of common errors.</p>
<pre><code class="language-js">fs.<span class="hljs-title function_">access</span>(<span class="hljs-string">'file/that/does/not/exist'</span>, <span class="hljs-function">(<span class="hljs-params">err</span>) =></span> {
<span class="hljs-keyword">const</span> errorMap = util.<span class="hljs-title function_">getSystemErrorMap</span>();
<span class="hljs-keyword">const</span> name = errorMap.<span class="hljs-title function_">get</span>(err.<span class="hljs-property">errno</span>);
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">error</span>(name); <span class="hljs-comment">// ENOENT</span>
});</code> <button class="copy-button">copy</button></pre>
</section><section><h3><code>util.inherits(constructor, superConstructor)</code><span><a class="mark" href="#utilinheritsconstructor-superconstructor" id="utilinheritsconstructor-superconstructor">#</a></span><a aria-hidden="true" class="legacy" id="util_util_inherits_constructor_superconstructor"></a></h3>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v5.0.0</td>
<td><p>The <code>constructor</code> parameter can refer to an ES6 class now.</p></td></tr>
<tr><td>v0.3.0</td>
<td><p><span>Added in: v0.3.0</span></p></td></tr>
</tbody></table>
</details>
</div>
<p></p><div class="api_stability api_stability_3"><a href="documentation.html#stability-index">Stability: 3</a> - Legacy: Use ES2015 class syntax and <code>extends</code> keyword instead.</div><p></p>
<ul>
<li><code>constructor</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></li>
<li><code>superConstructor</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></li>
</ul>
<p>Usage of <code>util.inherits()</code> is discouraged. Please use the ES6 <code>class</code> and
<code>extends</code> keywords to get language level inheritance support. Also note
that the two styles are <a href="https://github.com/nodejs/node/issues/4179">semantically incompatible</a>.</p>
<p>Inherit the prototype methods from one <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/constructor">constructor</a> into another. The
prototype of <code>constructor</code> will be set to a new object created from
<code>superConstructor</code>.</p>
<p>This mainly adds some input validation on top of
<code>Object.setPrototypeOf(constructor.prototype, superConstructor.prototype)</code>.
As an additional convenience, <code>superConstructor</code> will be accessible
through the <code>constructor.super_</code> property.</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);
<span class="hljs-keyword">const</span> <span class="hljs-title class_">EventEmitter</span> = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:events'</span>);
<span class="hljs-keyword">function</span> <span class="hljs-title function_">MyStream</span>(<span class="hljs-params"></span>) {
<span class="hljs-title class_">EventEmitter</span>.<span class="hljs-title function_">call</span>(<span class="hljs-variable language_">this</span>);
}
util.<span class="hljs-title function_">inherits</span>(<span class="hljs-title class_">MyStream</span>, <span class="hljs-title class_">EventEmitter</span>);
<span class="hljs-title class_">MyStream</span>.<span class="hljs-property"><span class="hljs-keyword">prototype</span></span>.<span class="hljs-property">write</span> = <span class="hljs-keyword">function</span>(<span class="hljs-params">data</span>) {
<span class="hljs-variable language_">this</span>.<span class="hljs-title function_">emit</span>(<span class="hljs-string">'data'</span>, data);
};
<span class="hljs-keyword">const</span> stream = <span class="hljs-keyword">new</span> <span class="hljs-title class_">MyStream</span>();
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(stream <span class="hljs-keyword">instanceof</span> <span class="hljs-title class_">EventEmitter</span>); <span class="hljs-comment">// true</span>
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-title class_">MyStream</span>.<span class="hljs-property">super_</span> === <span class="hljs-title class_">EventEmitter</span>); <span class="hljs-comment">// true</span>
stream.<span class="hljs-title function_">on</span>(<span class="hljs-string">'data'</span>, <span class="hljs-function">(<span class="hljs-params">data</span>) =></span> {
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">`Received data: "<span class="hljs-subst">${data}</span>"`</span>);
});
stream.<span class="hljs-title function_">write</span>(<span class="hljs-string">'It works!'</span>); <span class="hljs-comment">// Received data: "It works!"</span></code> <button class="copy-button">copy</button></pre>
<p>ES6 example using <code>class</code> and <code>extends</code>:</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> <span class="hljs-title class_">EventEmitter</span> = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:events'</span>);
<span class="hljs-keyword">class</span> <span class="hljs-title class_">MyStream</span> <span class="hljs-keyword">extends</span> <span class="hljs-title class_ inherited__">EventEmitter</span> {
<span class="hljs-title function_">write</span>(<span class="hljs-params">data</span>) {
<span class="hljs-variable language_">this</span>.<span class="hljs-title function_">emit</span>(<span class="hljs-string">'data'</span>, data);
}
}
<span class="hljs-keyword">const</span> stream = <span class="hljs-keyword">new</span> <span class="hljs-title class_">MyStream</span>();
stream.<span class="hljs-title function_">on</span>(<span class="hljs-string">'data'</span>, <span class="hljs-function">(<span class="hljs-params">data</span>) =></span> {
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">`Received data: "<span class="hljs-subst">${data}</span>"`</span>);
});
stream.<span class="hljs-title function_">write</span>(<span class="hljs-string">'With ES6'</span>);</code> <button class="copy-button">copy</button></pre>
</section><section><h3><code>util.inspect(object[, options])</code><span><a class="mark" href="#utilinspectobject-options" id="utilinspectobject-options">#</a></span><a aria-hidden="true" class="legacy" id="util_util_inspect_object_options"></a></h3>
</section><section><h3><code>util.inspect(object[, showHidden[, depth[, colors]]])</code><span><a class="mark" href="#utilinspectobject-showhidden-depth-colors" id="utilinspectobject-showhidden-depth-colors">#</a></span><a aria-hidden="true" class="legacy" id="util_util_inspect_object_showhidden_depth_colors"></a></h3>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v16.18.0</td>
<td><p>add support for <code>maxArrayLength</code> when inspecting <code>Set</code> and <code>Map</code>.</p></td></tr>
<tr><td>v17.3.0, v16.14.0</td>
<td><p>The <code>numericSeparator</code> option is supported now.</p></td></tr>
<tr><td>v13.0.0</td>
<td><p>Circular references now include a marker to the reference.</p></td></tr>
<tr><td>v14.6.0, v12.19.0</td>
<td><p>If <code>object</code> is from a different <code>vm.Context</code> now, a custom inspection function on it will not receive context-specific arguments anymore.</p></td></tr>
<tr><td>v13.13.0, v12.17.0</td>
<td><p>The <code>maxStringLength</code> option is supported now.</p></td></tr>
<tr><td>v13.5.0, v12.16.0</td>
<td><p>User defined prototype properties are inspected in case <code>showHidden</code> is <code>true</code>.</p></td></tr>
<tr><td>v12.0.0</td>
<td><p>The <code>compact</code> options default is changed to <code>3</code> and the <code>breakLength</code> options default is changed to <code>80</code>.</p></td></tr>
<tr><td>v12.0.0</td>
<td><p>Internal properties no longer appear in the context argument of a custom inspection function.</p></td></tr>
<tr><td>v11.11.0</td>
<td><p>The <code>compact</code> option accepts numbers for a new output mode.</p></td></tr>
<tr><td>v11.7.0</td>
<td><p>ArrayBuffers now also show their binary contents.</p></td></tr>
<tr><td>v11.5.0</td>
<td><p>The <code>getters</code> option is supported now.</p></td></tr>
<tr><td>v11.4.0</td>
<td><p>The <code>depth</code> default changed back to <code>2</code>.</p></td></tr>
<tr><td>v11.0.0</td>
<td><p>The <code>depth</code> default changed to <code>20</code>.</p></td></tr>
<tr><td>v11.0.0</td>
<td><p>The inspection output is now limited to about 128 MiB. Data above that size will not be fully inspected.</p></td></tr>
<tr><td>v10.12.0</td>
<td><p>The <code>sorted</code> option is supported now.</p></td></tr>
<tr><td>v10.6.0</td>
<td><p>Inspecting linked lists and similar objects is now possible up to the maximum call stack size.</p></td></tr>
<tr><td>v10.0.0</td>
<td><p>The <code>WeakMap</code> and <code>WeakSet</code> entries can now be inspected as well.</p></td></tr>
<tr><td>v9.9.0</td>
<td><p>The <code>compact</code> option is supported now.</p></td></tr>
<tr><td>v6.6.0</td>
<td><p>Custom inspection functions can now return <code>this</code>.</p></td></tr>
<tr><td>v6.3.0</td>
<td><p>The <code>breakLength</code> option is supported now.</p></td></tr>
<tr><td>v6.1.0</td>
<td><p>The <code>maxArrayLength</code> option is supported now; in particular, long arrays are truncated by default.</p></td></tr>
<tr><td>v6.1.0</td>
<td><p>The <code>showProxy</code> option is supported now.</p></td></tr>
<tr><td>v0.3.0</td>
<td><p><span>Added in: v0.3.0</span></p></td></tr>
</tbody></table>
</details>
</div>
<ul>
<li><code>object</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a> Any JavaScript primitive or <code>Object</code>.</li>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a>
<ul>
<li><code>showHidden</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> If <code>true</code>, <code>object</code>'s non-enumerable symbols and
properties are included in the formatted result. <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakMap"><code>WeakMap</code></a> and
<a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakSet"><code>WeakSet</code></a> entries are also included as well as user defined prototype
properties (excluding method properties). <strong>Default:</strong> <code>false</code>.</li>
<li><code>depth</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> Specifies the number of times to recurse while formatting
<code>object</code>. This is useful for inspecting large objects. To recurse up to
the maximum call stack size pass <code>Infinity</code> or <code>null</code>.
<strong>Default:</strong> <code>2</code>.</li>
<li><code>colors</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> If <code>true</code>, the output is styled with ANSI color
codes. Colors are customizable. See <a href="#customizing-utilinspect-colors">Customizing <code>util.inspect</code> colors</a>.
<strong>Default:</strong> <code>false</code>.</li>
<li><code>customInspect</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> If <code>false</code>,
<code>[util.inspect.custom](depth, opts, inspect)</code> functions are not invoked.
<strong>Default:</strong> <code>true</code>.</li>
<li><code>showProxy</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> If <code>true</code>, <code>Proxy</code> inspection includes
the <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Proxy#Terminology"><code>target</code> and <code>handler</code></a> objects. <strong>Default:</strong> <code>false</code>.</li>
<li><code>maxArrayLength</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><integer></a> Specifies the maximum number of <code>Array</code>,
<a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray"><code>TypedArray</code></a>, <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map"><code>Map</code></a>, <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set"><code>Set</code></a>, <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakMap"><code>WeakMap</code></a>,
and <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakSet"><code>WeakSet</code></a> elements to include when formatting.
Set to <code>null</code> or <code>Infinity</code> to show all elements. Set to <code>0</code> or
negative to show no elements. <strong>Default:</strong> <code>100</code>.</li>
<li><code>maxStringLength</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><integer></a> Specifies the maximum number of characters to
include when formatting. Set to <code>null</code> or <code>Infinity</code> to show all elements.
Set to <code>0</code> or negative to show no characters. <strong>Default:</strong> <code>10000</code>.</li>
<li><code>breakLength</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><integer></a> The length at which input values are split across
multiple lines. Set to <code>Infinity</code> to format the input as a single line
(in combination with <code>compact</code> set to <code>true</code> or any number >= <code>1</code>).
<strong>Default:</strong> <code>80</code>.</li>
<li><code>compact</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><integer></a> Setting this to <code>false</code> causes each object key
to be displayed on a new line. It will break on new lines in text that is
longer than <code>breakLength</code>. If set to a number, the most <code>n</code> inner elements
are united on a single line as long as all properties fit into
<code>breakLength</code>. Short array elements are also grouped together. For more
information, see the example below. <strong>Default:</strong> <code>3</code>.</li>
<li><code>sorted</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> If set to <code>true</code> or a function, all properties
of an object, and <code>Set</code> and <code>Map</code> entries are sorted in the resulting
string. If set to <code>true</code> the <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/sort">default sort</a> is used. If set to a function,
it is used as a <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/sort#Parameters">compare function</a>.</li>
<li><code>getters</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> If set to <code>true</code>, getters are inspected. If set
to <code>'get'</code>, only getters without a corresponding setter are inspected. If
set to <code>'set'</code>, only getters with a corresponding setter are inspected.
This might cause side effects depending on the getter function.
<strong>Default:</strong> <code>false</code>.</li>
<li><code>numericSeparator</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> If set to <code>true</code>, an underscore is used to
separate every three digits in all bigints and numbers.
<strong>Default:</strong> <code>false</code>.</li>
</ul>
</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> The representation of <code>object</code>.</li>
</ul>
<p>The <code>util.inspect()</code> method returns a string representation of <code>object</code> that is
intended for debugging. The output of <code>util.inspect</code> may change at any time
and should not be depended upon programmatically. Additional <code>options</code> may be
passed that alter the result.
<code>util.inspect()</code> will use the constructor's name and/or <code>@@toStringTag</code> to make
an identifiable tag for an inspected value.</p>
<pre><code class="language-js"><span class="hljs-keyword">class</span> <span class="hljs-title class_">Foo</span> {
get [<span class="hljs-title class_">Symbol</span>.<span class="hljs-property">toStringTag</span>]() {
<span class="hljs-keyword">return</span> <span class="hljs-string">'bar'</span>;
}
}
<span class="hljs-keyword">class</span> <span class="hljs-title class_">Bar</span> {}
<span class="hljs-keyword">const</span> baz = <span class="hljs-title class_">Object</span>.<span class="hljs-title function_">create</span>(<span class="hljs-literal">null</span>, { [<span class="hljs-title class_">Symbol</span>.<span class="hljs-property">toStringTag</span>]: { <span class="hljs-attr">value</span>: <span class="hljs-string">'foo'</span> } });
util.<span class="hljs-title function_">inspect</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Foo</span>()); <span class="hljs-comment">// 'Foo [bar] {}'</span>
util.<span class="hljs-title function_">inspect</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Bar</span>()); <span class="hljs-comment">// 'Bar {}'</span>
util.<span class="hljs-title function_">inspect</span>(baz); <span class="hljs-comment">// '[foo] {}'</span></code> <button class="copy-button">copy</button></pre>
<p>Circular references point to their anchor by using a reference index:</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> { inspect } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);
<span class="hljs-keyword">const</span> obj = {};
obj.<span class="hljs-property">a</span> = [obj];
obj.<span class="hljs-property">b</span> = {};
obj.<span class="hljs-property">b</span>.<span class="hljs-property">inner</span> = obj.<span class="hljs-property">b</span>;
obj.<span class="hljs-property">b</span>.<span class="hljs-property">obj</span> = obj;
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-title function_">inspect</span>(obj));
<span class="hljs-comment">// <ref *1> {</span>
<span class="hljs-comment">// a: [ [Circular *1] ],</span>
<span class="hljs-comment">// b: <ref *2> { inner: [Circular *2], obj: [Circular *1] }</span>
<span class="hljs-comment">// }</span></code> <button class="copy-button">copy</button></pre>
<p>The following example inspects all properties of the <code>util</code> object:</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(util.<span class="hljs-title function_">inspect</span>(util, { <span class="hljs-attr">showHidden</span>: <span class="hljs-literal">true</span>, <span class="hljs-attr">depth</span>: <span class="hljs-literal">null</span> }));</code> <button class="copy-button">copy</button></pre>
<p>The following example highlights the effect of the <code>compact</code> option:</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);
<span class="hljs-keyword">const</span> o = {
<span class="hljs-attr">a</span>: [<span class="hljs-number">1</span>, <span class="hljs-number">2</span>, [[
<span class="hljs-string">'Lorem ipsum dolor sit amet,\nconsectetur adipiscing elit, sed do '</span> +
<span class="hljs-string">'eiusmod \ntempor incididunt ut labore et dolore magna aliqua.'</span>,
<span class="hljs-string">'test'</span>,
<span class="hljs-string">'foo'</span>]], <span class="hljs-number">4</span>],
<span class="hljs-attr">b</span>: <span class="hljs-keyword">new</span> <span class="hljs-title class_">Map</span>([[<span class="hljs-string">'za'</span>, <span class="hljs-number">1</span>], [<span class="hljs-string">'zb'</span>, <span class="hljs-string">'test'</span>]]),
};
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(util.<span class="hljs-title function_">inspect</span>(o, { <span class="hljs-attr">compact</span>: <span class="hljs-literal">true</span>, <span class="hljs-attr">depth</span>: <span class="hljs-number">5</span>, <span class="hljs-attr">breakLength</span>: <span class="hljs-number">80</span> }));
<span class="hljs-comment">// { a:</span>
<span class="hljs-comment">// [ 1,</span>
<span class="hljs-comment">// 2,</span>
<span class="hljs-comment">// [ [ 'Lorem ipsum dolor sit amet,\nconsectetur [...]', // A long line</span>
<span class="hljs-comment">// 'test',</span>
<span class="hljs-comment">// 'foo' ] ],</span>
<span class="hljs-comment">// 4 ],</span>
<span class="hljs-comment">// b: Map(2) { 'za' => 1, 'zb' => 'test' } }</span>
<span class="hljs-comment">// Setting `compact` to false or an integer creates more reader friendly output.</span>
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(util.<span class="hljs-title function_">inspect</span>(o, { <span class="hljs-attr">compact</span>: <span class="hljs-literal">false</span>, <span class="hljs-attr">depth</span>: <span class="hljs-number">5</span>, <span class="hljs-attr">breakLength</span>: <span class="hljs-number">80</span> }));
<span class="hljs-comment">// {</span>
<span class="hljs-comment">// a: [</span>
<span class="hljs-comment">// 1,</span>
<span class="hljs-comment">// 2,</span>
<span class="hljs-comment">// [</span>
<span class="hljs-comment">// [</span>
<span class="hljs-comment">// 'Lorem ipsum dolor sit amet,\n' +</span>
<span class="hljs-comment">// 'consectetur adipiscing elit, sed do eiusmod \n' +</span>
<span class="hljs-comment">// 'tempor incididunt ut labore et dolore magna aliqua.',</span>
<span class="hljs-comment">// 'test',</span>
<span class="hljs-comment">// 'foo'</span>
<span class="hljs-comment">// ]</span>
<span class="hljs-comment">// ],</span>
<span class="hljs-comment">// 4</span>
<span class="hljs-comment">// ],</span>
<span class="hljs-comment">// b: Map(2) {</span>
<span class="hljs-comment">// 'za' => 1,</span>
<span class="hljs-comment">// 'zb' => 'test'</span>
<span class="hljs-comment">// }</span>
<span class="hljs-comment">// }</span>
<span class="hljs-comment">// Setting `breakLength` to e.g. 150 will print the "Lorem ipsum" text in a</span>
<span class="hljs-comment">// single line.</span></code> <button class="copy-button">copy</button></pre>
<p>The <code>showHidden</code> option allows <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakMap"><code>WeakMap</code></a> and <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakSet"><code>WeakSet</code></a> entries to be
inspected. If there are more entries than <code>maxArrayLength</code>, there is no
guarantee which entries are displayed. That means retrieving the same
<a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakSet"><code>WeakSet</code></a> entries twice may result in different output. Furthermore, entries
with no remaining strong references may be garbage collected at any time.</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> { inspect } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);
<span class="hljs-keyword">const</span> obj = { <span class="hljs-attr">a</span>: <span class="hljs-number">1</span> };
<span class="hljs-keyword">const</span> obj2 = { <span class="hljs-attr">b</span>: <span class="hljs-number">2</span> };
<span class="hljs-keyword">const</span> weakSet = <span class="hljs-keyword">new</span> <span class="hljs-title class_">WeakSet</span>([obj, obj2]);
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-title function_">inspect</span>(weakSet, { <span class="hljs-attr">showHidden</span>: <span class="hljs-literal">true</span> }));
<span class="hljs-comment">// WeakSet { { a: 1 }, { b: 2 } }</span></code> <button class="copy-button">copy</button></pre>
<p>The <code>sorted</code> option ensures that an object's property insertion order does not
impact the result of <code>util.inspect()</code>.</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> { inspect } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);
<span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert'</span>);
<span class="hljs-keyword">const</span> o1 = {
<span class="hljs-attr">b</span>: [<span class="hljs-number">2</span>, <span class="hljs-number">3</span>, <span class="hljs-number">1</span>],
<span class="hljs-attr">a</span>: <span class="hljs-string">'`a` comes before `b`'</span>,
<span class="hljs-attr">c</span>: <span class="hljs-keyword">new</span> <span class="hljs-title class_">Set</span>([<span class="hljs-number">2</span>, <span class="hljs-number">3</span>, <span class="hljs-number">1</span>]),
};
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-title function_">inspect</span>(o1, { <span class="hljs-attr">sorted</span>: <span class="hljs-literal">true</span> }));
<span class="hljs-comment">// { a: '`a` comes before `b`', b: [ 2, 3, 1 ], c: Set(3) { 1, 2, 3 } }</span>
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-title function_">inspect</span>(o1, { <span class="hljs-attr">sorted</span>: <span class="hljs-function">(<span class="hljs-params">a, b</span>) =></span> b.<span class="hljs-title function_">localeCompare</span>(a) }));
<span class="hljs-comment">// { c: Set(3) { 3, 2, 1 }, b: [ 2, 3, 1 ], a: '`a` comes before `b`' }</span>
<span class="hljs-keyword">const</span> o2 = {
<span class="hljs-attr">c</span>: <span class="hljs-keyword">new</span> <span class="hljs-title class_">Set</span>([<span class="hljs-number">2</span>, <span class="hljs-number">1</span>, <span class="hljs-number">3</span>]),
<span class="hljs-attr">a</span>: <span class="hljs-string">'`a` comes before `b`'</span>,
<span class="hljs-attr">b</span>: [<span class="hljs-number">2</span>, <span class="hljs-number">3</span>, <span class="hljs-number">1</span>],
};
assert.<span class="hljs-property">strict</span>.<span class="hljs-title function_">equal</span>(
<span class="hljs-title function_">inspect</span>(o1, { <span class="hljs-attr">sorted</span>: <span class="hljs-literal">true</span> }),
<span class="hljs-title function_">inspect</span>(o2, { <span class="hljs-attr">sorted</span>: <span class="hljs-literal">true</span> }),
);</code> <button class="copy-button">copy</button></pre>
<p>The <code>numericSeparator</code> option adds an underscore every three digits to all
numbers.</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> { inspect } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);
<span class="hljs-keyword">const</span> thousand = <span class="hljs-number">1_000</span>;
<span class="hljs-keyword">const</span> million = <span class="hljs-number">1_000_000</span>;
<span class="hljs-keyword">const</span> bigNumber = <span class="hljs-number">123_456_789n</span>;
<span class="hljs-keyword">const</span> bigDecimal = <span class="hljs-number">1_234.123_45</span>;
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-title function_">inspect</span>(thousand, { <span class="hljs-attr">numericSeparator</span>: <span class="hljs-literal">true</span> }));
<span class="hljs-comment">// 1_000</span>
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-title function_">inspect</span>(million, { <span class="hljs-attr">numericSeparator</span>: <span class="hljs-literal">true</span> }));
<span class="hljs-comment">// 1_000_000</span>
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-title function_">inspect</span>(bigNumber, { <span class="hljs-attr">numericSeparator</span>: <span class="hljs-literal">true</span> }));
<span class="hljs-comment">// 123_456_789n</span>
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-title function_">inspect</span>(bigDecimal, { <span class="hljs-attr">numericSeparator</span>: <span class="hljs-literal">true</span> }));
<span class="hljs-comment">// 1_234.123_45</span></code> <button class="copy-button">copy</button></pre>
<p><code>util.inspect()</code> is a synchronous method intended for debugging. Its maximum
output length is approximately 128 MiB. Inputs that result in longer output will
be truncated.</p>
<h4>Customizing <code>util.inspect</code> colors<span><a class="mark" href="#customizing-utilinspect-colors" id="customizing-utilinspect-colors">#</a></span><a aria-hidden="true" class="legacy" id="util_customizing_util_inspect_colors"></a></h4>
<p>Color output (if enabled) of <code>util.inspect</code> is customizable globally
via the <code>util.inspect.styles</code> and <code>util.inspect.colors</code> properties.</p>
<p><code>util.inspect.styles</code> is a map associating a style name to a color from
<code>util.inspect.colors</code>.</p>
<p>The default styles and associated colors are:</p>
<ul>
<li><code>bigint</code>: <code>yellow</code></li>
<li><code>boolean</code>: <code>yellow</code></li>
<li><code>date</code>: <code>magenta</code></li>
<li><code>module</code>: <code>underline</code></li>
<li><code>name</code>: (no styling)</li>
<li><code>null</code>: <code>bold</code></li>
<li><code>number</code>: <code>yellow</code></li>
<li><code>regexp</code>: <code>red</code></li>
<li><code>special</code>: <code>cyan</code> (e.g., <code>Proxies</code>)</li>
<li><code>string</code>: <code>green</code></li>
<li><code>symbol</code>: <code>green</code></li>
<li><code>undefined</code>: <code>grey</code></li>
</ul>
<p>Color styling uses ANSI control codes that may not be supported on all
terminals. To verify color support use <a href="tty.html#writestreamhascolorscount-env"><code>tty.hasColors()</code></a>.</p>
<p>Predefined control codes are listed below (grouped as "Modifiers", "Foreground
colors", and "Background colors").</p>
<h5>Modifiers<span><a class="mark" href="#modifiers" id="modifiers">#</a></span><a aria-hidden="true" class="legacy" id="util_modifiers"></a></h5>
<p>Modifier support varies throughout different terminals. They will mostly be
ignored, if not supported.</p>
<ul>
<li><code>reset</code> - Resets all (color) modifiers to their defaults</li>
<li><strong>bold</strong> - Make text bold</li>
<li><em>italic</em> - Make text italic</li>
<li><span style="border-bottom: 1px;">underline</span> - Make text underlined</li>
<li><del>strikethrough</del> - Puts a horizontal line through the center of the text
(Alias: <code>strikeThrough</code>, <code>crossedout</code>, <code>crossedOut</code>)</li>
<li><code>hidden</code> - Prints the text, but makes it invisible (Alias: conceal)</li>
<li><span style="opacity: 0.5;">dim</span> - Decreased color intensity (Alias:
<code>faint</code>)</li>
<li><span style="border-top: 1px">overlined</span> - Make text overlined</li>
<li>blink - Hides and shows the text in an interval</li>
<li><span style="filter: invert(100%)">inverse</span> - Swap foreground and
background colors (Alias: <code>swapcolors</code>, <code>swapColors</code>)</li>
<li><span style="border-bottom: 1px double;">doubleunderline</span> - Make text
double underlined (Alias: <code>doubleUnderline</code>)</li>
<li><span style="border: 1px">framed</span> - Draw a frame around the text</li>
</ul>
<h5>Foreground colors<span><a class="mark" href="#foreground-colors" id="foreground-colors">#</a></span><a aria-hidden="true" class="legacy" id="util_foreground_colors"></a></h5>
<ul>
<li><code>black</code></li>
<li><code>red</code></li>
<li><code>green</code></li>
<li><code>yellow</code></li>
<li><code>blue</code></li>
<li><code>magenta</code></li>
<li><code>cyan</code></li>
<li><code>white</code></li>
<li><code>gray</code> (alias: <code>grey</code>, <code>blackBright</code>)</li>
<li><code>redBright</code></li>
<li><code>greenBright</code></li>
<li><code>yellowBright</code></li>
<li><code>blueBright</code></li>
<li><code>magentaBright</code></li>
<li><code>cyanBright</code></li>
<li><code>whiteBright</code></li>
</ul>
<h5>Background colors<span><a class="mark" href="#background-colors" id="background-colors">#</a></span><a aria-hidden="true" class="legacy" id="util_background_colors"></a></h5>
<ul>
<li><code>bgBlack</code></li>
<li><code>bgRed</code></li>
<li><code>bgGreen</code></li>
<li><code>bgYellow</code></li>
<li><code>bgBlue</code></li>
<li><code>bgMagenta</code></li>
<li><code>bgCyan</code></li>
<li><code>bgWhite</code></li>
<li><code>bgGray</code> (alias: <code>bgGrey</code>, <code>bgBlackBright</code>)</li>
<li><code>bgRedBright</code></li>
<li><code>bgGreenBright</code></li>
<li><code>bgYellowBright</code></li>
<li><code>bgBlueBright</code></li>
<li><code>bgMagentaBright</code></li>
<li><code>bgCyanBright</code></li>
<li><code>bgWhiteBright</code></li>
</ul>
<h4>Custom inspection functions on objects<span><a class="mark" href="#custom-inspection-functions-on-objects" id="custom-inspection-functions-on-objects">#</a></span><a aria-hidden="true" class="legacy" id="util_custom_inspection_functions_on_objects"></a></h4>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v17.3.0, v16.14.0</td>
<td><p>The inspect argument is added for more interoperability.</p></td></tr>
<tr><td>v0.1.97</td>
<td><p><span>Added in: v0.1.97</span></p></td></tr>
</tbody></table>
</details>
</div>
<p>Objects may also define their own
<a href="#utilinspectcustom"><code>[util.inspect.custom](depth, opts, inspect)</code></a> function,
which <code>util.inspect()</code> will invoke and use the result of when inspecting
the object.</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);
<span class="hljs-keyword">class</span> <span class="hljs-title class_">Box</span> {
<span class="hljs-title function_">constructor</span>(<span class="hljs-params">value</span>) {
<span class="hljs-variable language_">this</span>.<span class="hljs-property">value</span> = value;
}
[util.<span class="hljs-property">inspect</span>.<span class="hljs-property">custom</span>](depth, options, inspect) {
<span class="hljs-keyword">if</span> (depth < <span class="hljs-number">0</span>) {
<span class="hljs-keyword">return</span> options.<span class="hljs-title function_">stylize</span>(<span class="hljs-string">'[Box]'</span>, <span class="hljs-string">'special'</span>);
}
<span class="hljs-keyword">const</span> newOptions = <span class="hljs-title class_">Object</span>.<span class="hljs-title function_">assign</span>({}, options, {
<span class="hljs-attr">depth</span>: options.<span class="hljs-property">depth</span> === <span class="hljs-literal">null</span> ? <span class="hljs-literal">null</span> : options.<span class="hljs-property">depth</span> - <span class="hljs-number">1</span>,
});
<span class="hljs-comment">// Five space padding because that's the size of "Box< ".</span>
<span class="hljs-keyword">const</span> padding = <span class="hljs-string">' '</span>.<span class="hljs-title function_">repeat</span>(<span class="hljs-number">5</span>);
<span class="hljs-keyword">const</span> inner = <span class="hljs-title function_">inspect</span>(<span class="hljs-variable language_">this</span>.<span class="hljs-property">value</span>, newOptions)
.<span class="hljs-title function_">replace</span>(<span class="hljs-regexp">/\n/g</span>, <span class="hljs-string">`\n<span class="hljs-subst">${padding}</span>`</span>);
<span class="hljs-keyword">return</span> <span class="hljs-string">`<span class="hljs-subst">${options.stylize(<span class="hljs-string">'Box'</span>, <span class="hljs-string">'special'</span>)}</span>< <span class="hljs-subst">${inner}</span> >`</span>;
}
}
<span class="hljs-keyword">const</span> box = <span class="hljs-keyword">new</span> <span class="hljs-title class_">Box</span>(<span class="hljs-literal">true</span>);
util.<span class="hljs-title function_">inspect</span>(box);
<span class="hljs-comment">// Returns: "Box< true >"</span></code> <button class="copy-button">copy</button></pre>
<p>Custom <code>[util.inspect.custom](depth, opts, inspect)</code> functions typically return
a string but may return a value of any type that will be formatted accordingly
by <code>util.inspect()</code>.</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);
<span class="hljs-keyword">const</span> obj = { <span class="hljs-attr">foo</span>: <span class="hljs-string">'this will not show up in the inspect() output'</span> };
obj[util.<span class="hljs-property">inspect</span>.<span class="hljs-property">custom</span>] = <span class="hljs-function">(<span class="hljs-params">depth</span>) =></span> {
<span class="hljs-keyword">return</span> { <span class="hljs-attr">bar</span>: <span class="hljs-string">'baz'</span> };
};
util.<span class="hljs-title function_">inspect</span>(obj);
<span class="hljs-comment">// Returns: "{ bar: 'baz' }"</span></code> <button class="copy-button">copy</button></pre>
<h4><code>util.inspect.custom</code><span><a class="mark" href="#utilinspectcustom" id="utilinspectcustom">#</a></span><a aria-hidden="true" class="legacy" id="util_util_inspect_custom"></a></h4>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v10.12.0</td>
<td><p>This is now defined as a shared symbol.</p></td></tr>
<tr><td>v6.6.0</td>
<td><p><span>Added in: v6.6.0</span></p></td></tr>
</tbody></table>
</details>
</div>
<ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Symbol_type" class="type"><symbol></a> that can be used to declare custom inspect functions.</li>
</ul>
<p>In addition to being accessible through <code>util.inspect.custom</code>, this
symbol is <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol/for">registered globally</a> and can be
accessed in any environment as <code>Symbol.for('nodejs.util.inspect.custom')</code>.</p>
<p>Using this allows code to be written in a portable fashion, so that the custom
inspect function is used in an Node.js environment and ignored in the browser.
The <code>util.inspect()</code> function itself is passed as third argument to the custom
inspect function to allow further portability.</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> customInspectSymbol = <span class="hljs-title class_">Symbol</span>.<span class="hljs-title function_">for</span>(<span class="hljs-string">'nodejs.util.inspect.custom'</span>);
<span class="hljs-keyword">class</span> <span class="hljs-title class_">Password</span> {
<span class="hljs-title function_">constructor</span>(<span class="hljs-params">value</span>) {
<span class="hljs-variable language_">this</span>.<span class="hljs-property">value</span> = value;
}
<span class="hljs-title function_">toString</span>(<span class="hljs-params"></span>) {
<span class="hljs-keyword">return</span> <span class="hljs-string">'xxxxxxxx'</span>;
}
[customInspectSymbol](depth, inspectOptions, inspect) {
<span class="hljs-keyword">return</span> <span class="hljs-string">`Password <<span class="hljs-subst">${<span class="hljs-variable language_">this</span>.toString()}</span>>`</span>;
}
}
<span class="hljs-keyword">const</span> password = <span class="hljs-keyword">new</span> <span class="hljs-title class_">Password</span>(<span class="hljs-string">'r0sebud'</span>);
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(password);
<span class="hljs-comment">// Prints Password <xxxxxxxx></span></code> <button class="copy-button">copy</button></pre>
<p>See <a href="#custom-inspection-functions-on-objects">Custom inspection functions on Objects</a> for more details.</p>
<h4><code>util.inspect.defaultOptions</code><span><a class="mark" href="#utilinspectdefaultoptions" id="utilinspectdefaultoptions">#</a></span><a aria-hidden="true" class="legacy" id="util_util_inspect_defaultoptions"></a></h4>
<div class="api_metadata">
<span>Added in: v6.4.0</span>
</div>
<p>The <code>defaultOptions</code> value allows customization of the default options used by
<code>util.inspect</code>. This is useful for functions like <code>console.log</code> or
<code>util.format</code> which implicitly call into <code>util.inspect</code>. It shall be set to an
object containing one or more valid <a href="#utilinspectobject-options"><code>util.inspect()</code></a> options. Setting
option properties directly is also supported.</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);
<span class="hljs-keyword">const</span> arr = <span class="hljs-title class_">Array</span>(<span class="hljs-number">101</span>).<span class="hljs-title function_">fill</span>(<span class="hljs-number">0</span>);
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(arr); <span class="hljs-comment">// Logs the truncated array</span>
util.<span class="hljs-property">inspect</span>.<span class="hljs-property">defaultOptions</span>.<span class="hljs-property">maxArrayLength</span> = <span class="hljs-literal">null</span>;
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(arr); <span class="hljs-comment">// logs the full array</span></code> <button class="copy-button">copy</button></pre>
</section><section><h3><code>util.isDeepStrictEqual(val1, val2)</code><span><a class="mark" href="#utilisdeepstrictequalval1-val2" id="utilisdeepstrictequalval1-val2">#</a></span><a aria-hidden="true" class="legacy" id="util_util_isdeepstrictequal_val1_val2"></a></h3>
<div class="api_metadata">
<span>Added in: v9.0.0</span>
</div>
<ul>
<li><code>val1</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li><code>val2</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if there is deep strict equality between <code>val1</code> and <code>val2</code>.
Otherwise, returns <code>false</code>.</p>
<p>See <a href="assert.html#assertdeepstrictequalactual-expected-message"><code>assert.deepStrictEqual()</code></a> for more information about deep strict
equality.</p>
</section><section><h3>Class: <code>util.MIMEType</code><span><a class="mark" href="#class-utilmimetype" id="class-utilmimetype">#</a></span><a aria-hidden="true" class="legacy" id="util_class_util_mimetype"></a></h3>
<div class="api_metadata">
<span>Added in: v19.1.0, v18.13.0</span>
</div>
<p></p><div class="api_stability api_stability_1"><a href="documentation.html#stability-index">Stability: 1</a> - Experimental</div><p></p>
<p>An implementation of <a href="https://bmeck.github.io/node-proposal-mime-api/">the MIMEType class</a>.</p>
<p>In accordance with browser conventions, all properties of <code>MIMEType</code> objects
are implemented as getters and setters on the class prototype, rather than as
data properties on the object itself.</p>
<p>A MIME string is a structured string containing multiple meaningful
components. When parsed, a <code>MIMEType</code> object is returned containing
properties for each of these components.</p>
<h4>Constructor: <code>new MIMEType(input)</code><span><a class="mark" href="#constructor-new-mimetypeinput" id="constructor-new-mimetypeinput">#</a></span><a aria-hidden="true" class="legacy" id="util_constructor_new_mimetype_input"></a></h4>
<ul>
<li><code>input</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> The input MIME to parse</li>
</ul>
<p>Creates a new <code>MIMEType</code> object by parsing the <code>input</code>.</p>
<pre class="with-42-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> { <span class="hljs-title class_">MIMEType</span> } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:util'</span>;
<span class="hljs-keyword">const</span> myMIME = <span class="hljs-keyword">new</span> <span class="hljs-title class_">MIMEType</span>(<span class="hljs-string">'text/plain'</span>);</code><code class="language-js cjs"><span class="hljs-keyword">const</span> { <span class="hljs-title class_">MIMEType</span> } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);
<span class="hljs-keyword">const</span> myMIME = <span class="hljs-keyword">new</span> <span class="hljs-title class_">MIMEType</span>(<span class="hljs-string">'text/plain'</span>);</code><button class="copy-button">copy</button></pre>
<p>A <code>TypeError</code> will be thrown if the <code>input</code> is not a valid MIME. Note
that an effort will be made to coerce the given values into strings. For
instance:</p>
<pre class="with-62-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> { <span class="hljs-title class_">MIMEType</span> } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:util'</span>;
<span class="hljs-keyword">const</span> myMIME = <span class="hljs-keyword">new</span> <span class="hljs-title class_">MIMEType</span>({ <span class="hljs-attr">toString</span>: <span class="hljs-function">() =></span> <span class="hljs-string">'text/plain'</span> });
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-title class_">String</span>(myMIME));
<span class="hljs-comment">// Prints: text/plain</span></code><code class="language-js cjs"><span class="hljs-keyword">const</span> { <span class="hljs-title class_">MIMEType</span> } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);
<span class="hljs-keyword">const</span> myMIME = <span class="hljs-keyword">new</span> <span class="hljs-title class_">MIMEType</span>({ <span class="hljs-attr">toString</span>: <span class="hljs-function">() =></span> <span class="hljs-string">'text/plain'</span> });
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-title class_">String</span>(myMIME));
<span class="hljs-comment">// Prints: text/plain</span></code><button class="copy-button">copy</button></pre>
<h4><code>mime.type</code><span><a class="mark" href="#mimetype" id="mimetype">#</a></span><a aria-hidden="true" class="legacy" id="util_mime_type"></a></h4>
<ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li>
</ul>
<p>Gets and sets the type portion of the MIME.</p>
<pre class="with-42-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> { <span class="hljs-title class_">MIMEType</span> } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:util'</span>;
<span class="hljs-keyword">const</span> myMIME = <span class="hljs-keyword">new</span> <span class="hljs-title class_">MIMEType</span>(<span class="hljs-string">'text/javascript'</span>);
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(myMIME.<span class="hljs-property">type</span>);
<span class="hljs-comment">// Prints: text</span>
myMIME.<span class="hljs-property">type</span> = <span class="hljs-string">'application'</span>;
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(myMIME.<span class="hljs-property">type</span>);
<span class="hljs-comment">// Prints: application</span>
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-title class_">String</span>(myMIME));
<span class="hljs-comment">// Prints: application/javascript</span></code><code class="language-js cjs"><span class="hljs-keyword">const</span> { <span class="hljs-title class_">MIMEType</span> } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);
<span class="hljs-keyword">const</span> myMIME = <span class="hljs-keyword">new</span> <span class="hljs-title class_">MIMEType</span>(<span class="hljs-string">'text/javascript'</span>);
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(myMIME.<span class="hljs-property">type</span>);
<span class="hljs-comment">// Prints: text</span>
myMIME.<span class="hljs-property">type</span> = <span class="hljs-string">'application'</span>;
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(myMIME.<span class="hljs-property">type</span>);
<span class="hljs-comment">// Prints: application</span>
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-title class_">String</span>(myMIME));
<span class="hljs-comment">// Prints: application/javascript</span></code><button class="copy-button">copy</button></pre>
<h4><code>mime.subtype</code><span><a class="mark" href="#mimesubtype" id="mimesubtype">#</a></span><a aria-hidden="true" class="legacy" id="util_mime_subtype"></a></h4>
<ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li>
</ul>
<p>Gets and sets the subtype portion of the MIME.</p>
<pre class="with-42-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> { <span class="hljs-title class_">MIMEType</span> } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:util'</span>;
<span class="hljs-keyword">const</span> myMIME = <span class="hljs-keyword">new</span> <span class="hljs-title class_">MIMEType</span>(<span class="hljs-string">'text/ecmascript'</span>);
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(myMIME.<span class="hljs-property">subtype</span>);
<span class="hljs-comment">// Prints: ecmascript</span>
myMIME.<span class="hljs-property">subtype</span> = <span class="hljs-string">'javascript'</span>;
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(myMIME.<span class="hljs-property">subtype</span>);
<span class="hljs-comment">// Prints: javascript</span>
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-title class_">String</span>(myMIME));
<span class="hljs-comment">// Prints: text/javascript</span></code><code class="language-js cjs"><span class="hljs-keyword">const</span> { <span class="hljs-title class_">MIMEType</span> } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);
<span class="hljs-keyword">const</span> myMIME = <span class="hljs-keyword">new</span> <span class="hljs-title class_">MIMEType</span>(<span class="hljs-string">'text/ecmascript'</span>);
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(myMIME.<span class="hljs-property">subtype</span>);
<span class="hljs-comment">// Prints: ecmascript</span>
myMIME.<span class="hljs-property">subtype</span> = <span class="hljs-string">'javascript'</span>;
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(myMIME.<span class="hljs-property">subtype</span>);
<span class="hljs-comment">// Prints: javascript</span>
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-title class_">String</span>(myMIME));
<span class="hljs-comment">// Prints: text/javascript</span></code><button class="copy-button">copy</button></pre>
<h4><code>mime.essence</code><span><a class="mark" href="#mimeessence" id="mimeessence">#</a></span><a aria-hidden="true" class="legacy" id="util_mime_essence"></a></h4>
<ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li>
</ul>
<p>Gets the essence of the MIME. This property is read only.
Use <code>mime.type</code> or <code>mime.subtype</code> to alter the MIME.</p>
<pre class="with-42-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> { <span class="hljs-title class_">MIMEType</span> } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:util'</span>;
<span class="hljs-keyword">const</span> myMIME = <span class="hljs-keyword">new</span> <span class="hljs-title class_">MIMEType</span>(<span class="hljs-string">'text/javascript;key=value'</span>);
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(myMIME.<span class="hljs-property">essence</span>);
<span class="hljs-comment">// Prints: text/javascript</span>
myMIME.<span class="hljs-property">type</span> = <span class="hljs-string">'application'</span>;
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(myMIME.<span class="hljs-property">essence</span>);
<span class="hljs-comment">// Prints: application/javascript</span>
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-title class_">String</span>(myMIME));
<span class="hljs-comment">// Prints: application/javascript;key=value</span></code><code class="language-js cjs"><span class="hljs-keyword">const</span> { <span class="hljs-title class_">MIMEType</span> } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);
<span class="hljs-keyword">const</span> myMIME = <span class="hljs-keyword">new</span> <span class="hljs-title class_">MIMEType</span>(<span class="hljs-string">'text/javascript;key=value'</span>);
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(myMIME.<span class="hljs-property">essence</span>);
<span class="hljs-comment">// Prints: text/javascript</span>
myMIME.<span class="hljs-property">type</span> = <span class="hljs-string">'application'</span>;
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(myMIME.<span class="hljs-property">essence</span>);
<span class="hljs-comment">// Prints: application/javascript</span>
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-title class_">String</span>(myMIME));
<span class="hljs-comment">// Prints: application/javascript;key=value</span></code><button class="copy-button">copy</button></pre>
<h4><code>mime.params</code><span><a class="mark" href="#mimeparams" id="mimeparams">#</a></span><a aria-hidden="true" class="legacy" id="util_mime_params"></a></h4>
<ul>
<li><a href="util.html#class-utilmimeparams" class="type"><MIMEParams></a></li>
</ul>
<p>Gets the <a href="#class-utilmimeparams"><code>MIMEParams</code></a> object representing the
parameters of the MIME. This property is read-only. See
<a href="#class-utilmimeparams"><code>MIMEParams</code></a> documentation for details.</p>
<h4><code>mime.toString()</code><span><a class="mark" href="#mimetostring" id="mimetostring">#</a></span><a aria-hidden="true" class="legacy" id="util_mime_tostring"></a></h4>
<ul>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li>
</ul>
<p>The <code>toString()</code> method on the <code>MIMEType</code> object returns the serialized MIME.</p>
<p>Because of the need for standard compliance, this method does not allow users
to customize the serialization process of the MIME.</p>
<h4><code>mime.toJSON()</code><span><a class="mark" href="#mimetojson" id="mimetojson">#</a></span><a aria-hidden="true" class="legacy" id="util_mime_tojson"></a></h4>
<ul>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li>
</ul>
<p>Alias for <a href="#mimetostring"><code>mime.toString()</code></a>.</p>
<p>This method is automatically called when an <code>MIMEType</code> object is serialized
with <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/stringify"><code>JSON.stringify()</code></a>.</p>
<pre class="with-42-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> { <span class="hljs-title class_">MIMEType</span> } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:util'</span>;
<span class="hljs-keyword">const</span> myMIMES = [
<span class="hljs-keyword">new</span> <span class="hljs-title class_">MIMEType</span>(<span class="hljs-string">'image/png'</span>),
<span class="hljs-keyword">new</span> <span class="hljs-title class_">MIMEType</span>(<span class="hljs-string">'image/gif'</span>),
];
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-title class_">JSON</span>.<span class="hljs-title function_">stringify</span>(myMIMES));
<span class="hljs-comment">// Prints: ["image/png", "image/gif"]</span></code><code class="language-js cjs"><span class="hljs-keyword">const</span> { <span class="hljs-title class_">MIMEType</span> } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);
<span class="hljs-keyword">const</span> myMIMES = [
<span class="hljs-keyword">new</span> <span class="hljs-title class_">MIMEType</span>(<span class="hljs-string">'image/png'</span>),
<span class="hljs-keyword">new</span> <span class="hljs-title class_">MIMEType</span>(<span class="hljs-string">'image/gif'</span>),
];
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-title class_">JSON</span>.<span class="hljs-title function_">stringify</span>(myMIMES));
<span class="hljs-comment">// Prints: ["image/png", "image/gif"]</span></code><button class="copy-button">copy</button></pre>
</section><section><h3>Class: <code>util.MIMEParams</code><span><a class="mark" href="#class-utilmimeparams" id="class-utilmimeparams">#</a></span><a aria-hidden="true" class="legacy" id="util_class_util_mimeparams"></a></h3>
<div class="api_metadata">
<span>Added in: v19.1.0, v18.13.0</span>
</div>
<p>The <code>MIMEParams</code> API provides read and write access to the parameters of a
<code>MIMEType</code>.</p>
<h4>Constructor: <code>new MIMEParams()</code><span><a class="mark" href="#constructor-new-mimeparams" id="constructor-new-mimeparams">#</a></span><a aria-hidden="true" class="legacy" id="util_constructor_new_mimeparams"></a></h4>
<p>Creates a new <code>MIMEParams</code> object by with empty parameters</p>
<pre class="with-44-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> { <span class="hljs-title class_">MIMEParams</span> } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:util'</span>;
<span class="hljs-keyword">const</span> myParams = <span class="hljs-keyword">new</span> <span class="hljs-title class_">MIMEParams</span>();</code><code class="language-js cjs"><span class="hljs-keyword">const</span> { <span class="hljs-title class_">MIMEParams</span> } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);
<span class="hljs-keyword">const</span> myParams = <span class="hljs-keyword">new</span> <span class="hljs-title class_">MIMEParams</span>();</code><button class="copy-button">copy</button></pre>
<h4><code>mimeParams.delete(name)</code><span><a class="mark" href="#mimeparamsdeletename" id="mimeparamsdeletename">#</a></span><a aria-hidden="true" class="legacy" id="util_mimeparams_delete_name"></a></h4>
<ul>
<li><code>name</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li>
</ul>
<p>Remove all name-value pairs whose name is <code>name</code>.</p>
<h4><code>mimeParams.entries()</code><span><a class="mark" href="#mimeparamsentries" id="mimeparamsentries">#</a></span><a aria-hidden="true" class="legacy" id="util_mimeparams_entries"></a></h4>
<ul>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols#The_iterator_protocol" class="type"><Iterator></a></li>
</ul>
<p>Returns an iterator over each of the name-value pairs in the parameters.
Each item of the iterator is a JavaScript <code>Array</code>. The first item of the array
is the <code>name</code>, the second item of the array is the <code>value</code>.</p>
<h4><code>mimeParams.get(name)</code><span><a class="mark" href="#mimeparamsgetname" id="mimeparamsgetname">#</a></span><a aria-hidden="true" class="legacy" id="util_mimeparams_get_name"></a></h4>
<ul>
<li><code>name</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type" class="type"><null></a> A string or <code>null</code> if there is no name-value pair
with the given <code>name</code>.</li>
</ul>
<p>Returns the value of the first name-value pair whose name is <code>name</code>. If there
are no such pairs, <code>null</code> is returned.</p>
<h4><code>mimeParams.has(name)</code><span><a class="mark" href="#mimeparamshasname" id="mimeparamshasname">#</a></span><a aria-hidden="true" class="legacy" id="util_mimeparams_has_name"></a></h4>
<ul>
<li><code>name</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if there is at least one name-value pair whose name is <code>name</code>.</p>
<h4><code>mimeParams.keys()</code><span><a class="mark" href="#mimeparamskeys" id="mimeparamskeys">#</a></span><a aria-hidden="true" class="legacy" id="util_mimeparams_keys"></a></h4>
<ul>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols#The_iterator_protocol" class="type"><Iterator></a></li>
</ul>
<p>Returns an iterator over the names of each name-value pair.</p>
<pre class="with-42-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> { <span class="hljs-title class_">MIMEType</span> } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:util'</span>;
<span class="hljs-keyword">const</span> { params } = <span class="hljs-keyword">new</span> <span class="hljs-title class_">MIMEType</span>(<span class="hljs-string">'text/plain;foo=0;bar=1'</span>);
<span class="hljs-keyword">for</span> (<span class="hljs-keyword">const</span> name <span class="hljs-keyword">of</span> params.<span class="hljs-title function_">keys</span>()) {
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(name);
}
<span class="hljs-comment">// Prints:</span>
<span class="hljs-comment">// foo</span>
<span class="hljs-comment">// bar</span></code><code class="language-js cjs"><span class="hljs-keyword">const</span> { <span class="hljs-title class_">MIMEType</span> } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);
<span class="hljs-keyword">const</span> { params } = <span class="hljs-keyword">new</span> <span class="hljs-title class_">MIMEType</span>(<span class="hljs-string">'text/plain;foo=0;bar=1'</span>);
<span class="hljs-keyword">for</span> (<span class="hljs-keyword">const</span> name <span class="hljs-keyword">of</span> params.<span class="hljs-title function_">keys</span>()) {
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(name);
}
<span class="hljs-comment">// Prints:</span>
<span class="hljs-comment">// foo</span>
<span class="hljs-comment">// bar</span></code><button class="copy-button">copy</button></pre>
<h4><code>mimeParams.set(name, value)</code><span><a class="mark" href="#mimeparamssetname-value" id="mimeparamssetname-value">#</a></span><a aria-hidden="true" class="legacy" id="util_mimeparams_set_name_value"></a></h4>
<ul>
<li><code>name</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li>
</ul>
<p>Sets the value in the <code>MIMEParams</code> object associated with <code>name</code> to
<code>value</code>. If there are any pre-existing name-value pairs whose names are <code>name</code>,
set the first such pair's value to <code>value</code>.</p>
<pre class="with-42-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> { <span class="hljs-title class_">MIMEType</span> } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:util'</span>;
<span class="hljs-keyword">const</span> { params } = <span class="hljs-keyword">new</span> <span class="hljs-title class_">MIMEType</span>(<span class="hljs-string">'text/plain;foo=0;bar=1'</span>);
params.<span class="hljs-title function_">set</span>(<span class="hljs-string">'foo'</span>, <span class="hljs-string">'def'</span>);
params.<span class="hljs-title function_">set</span>(<span class="hljs-string">'baz'</span>, <span class="hljs-string">'xyz'</span>);
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(params.<span class="hljs-title function_">toString</span>());
<span class="hljs-comment">// Prints: foo=def;bar=1;baz=xyz</span></code><code class="language-js cjs"><span class="hljs-keyword">const</span> { <span class="hljs-title class_">MIMEType</span> } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);
<span class="hljs-keyword">const</span> { params } = <span class="hljs-keyword">new</span> <span class="hljs-title class_">MIMEType</span>(<span class="hljs-string">'text/plain;foo=0;bar=1'</span>);
params.<span class="hljs-title function_">set</span>(<span class="hljs-string">'foo'</span>, <span class="hljs-string">'def'</span>);
params.<span class="hljs-title function_">set</span>(<span class="hljs-string">'baz'</span>, <span class="hljs-string">'xyz'</span>);
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(params.<span class="hljs-title function_">toString</span>());
<span class="hljs-comment">// Prints: foo=def;bar=1;baz=xyz</span></code><button class="copy-button">copy</button></pre>
<h4><code>mimeParams.values()</code><span><a class="mark" href="#mimeparamsvalues" id="mimeparamsvalues">#</a></span><a aria-hidden="true" class="legacy" id="util_mimeparams_values"></a></h4>
<ul>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols#The_iterator_protocol" class="type"><Iterator></a></li>
</ul>
<p>Returns an iterator over the values of each name-value pair.</p>
<h4><code>mimeParams[@@iterator]()</code><span><a class="mark" href="#mimeparamsiterator" id="mimeparamsiterator">#</a></span><a aria-hidden="true" class="legacy" id="util_mimeparams_iterator"></a></h4>
<ul>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols#The_iterator_protocol" class="type"><Iterator></a></li>
</ul>
<p>Alias for <a href="#mimeparamsentries"><code>mimeParams.entries()</code></a>.</p>
<pre class="with-42-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> { <span class="hljs-title class_">MIMEType</span> } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:util'</span>;
<span class="hljs-keyword">const</span> { params } = <span class="hljs-keyword">new</span> <span class="hljs-title class_">MIMEType</span>(<span class="hljs-string">'text/plain;foo=bar;xyz=baz'</span>);
<span class="hljs-keyword">for</span> (<span class="hljs-keyword">const</span> [name, value] <span class="hljs-keyword">of</span> params) {
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(name, value);
}
<span class="hljs-comment">// Prints:</span>
<span class="hljs-comment">// foo bar</span>
<span class="hljs-comment">// xyz baz</span></code><code class="language-js cjs"><span class="hljs-keyword">const</span> { <span class="hljs-title class_">MIMEType</span> } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);
<span class="hljs-keyword">const</span> { params } = <span class="hljs-keyword">new</span> <span class="hljs-title class_">MIMEType</span>(<span class="hljs-string">'text/plain;foo=bar;xyz=baz'</span>);
<span class="hljs-keyword">for</span> (<span class="hljs-keyword">const</span> [name, value] <span class="hljs-keyword">of</span> params) {
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(name, value);
}
<span class="hljs-comment">// Prints:</span>
<span class="hljs-comment">// foo bar</span>
<span class="hljs-comment">// xyz baz</span></code><button class="copy-button">copy</button></pre>
</section><section><h3><code>util.parseArgs([config])</code><span><a class="mark" href="#utilparseargsconfig" id="utilparseargsconfig">#</a></span><a aria-hidden="true" class="legacy" id="util_util_parseargs_config"></a></h3>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v20.0.0</td>
<td><p>The API is no longer experimental.</p></td></tr>
<tr><td>v18.11.0, v16.19.0</td>
<td><p>Add support for default values in input <code>config</code>.</p></td></tr>
<tr><td>v18.7.0, v16.17.0</td>
<td><p>add support for returning detailed parse information using <code>tokens</code> in input <code>config</code> and returned properties.</p></td></tr>
<tr><td>v18.3.0, v16.17.0</td>
<td><p><span>Added in: v18.3.0, v16.17.0</span></p></td></tr>
</tbody></table>
</details>
</div>
<ul>
<li>
<p><code>config</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> Used to provide arguments for parsing and to configure
the parser. <code>config</code> supports the following properties:</p>
<ul>
<li><code>args</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string[]></a> array of argument strings. <strong>Default:</strong> <code>process.argv</code>
with <code>execPath</code> and <code>filename</code> removed.</li>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> Used to describe arguments known to the parser.
Keys of <code>options</code> are the long names of options and values are an
<a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> accepting the following properties:
<ul>
<li><code>type</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> Type of argument, which must be either <code>boolean</code> or <code>string</code>.</li>
<li><code>multiple</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> Whether this option can be provided multiple
times. If <code>true</code>, all values will be collected in an array. If
<code>false</code>, values for the option are last-wins. <strong>Default:</strong> <code>false</code>.</li>
<li><code>short</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> A single character alias for the option.</li>
<li><code>default</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string[]></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean[]></a> The default option
value when it is not set by args. It must be of the same type as the
<code>type</code> property. When <code>multiple</code> is <code>true</code>, it must be an array.</li>
</ul>
</li>
<li><code>strict</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> Should an error be thrown when unknown arguments
are encountered, or when arguments are passed that do not match the
<code>type</code> configured in <code>options</code>.
<strong>Default:</strong> <code>true</code>.</li>
<li><code>allowPositionals</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> Whether this command accepts positional
arguments.
<strong>Default:</strong> <code>false</code> if <code>strict</code> is <code>true</code>, otherwise <code>true</code>.</li>
<li><code>tokens</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> Return the parsed tokens. This is useful for extending
the built-in behavior, from adding additional checks through to reprocessing
the tokens in different ways.
<strong>Default:</strong> <code>false</code>.</li>
</ul>
</li>
<li>
<p>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> The parsed command line arguments:</p>
<ul>
<li><code>values</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> A mapping of parsed option names with their <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a>
or <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> values.</li>
<li><code>positionals</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string[]></a> Positional arguments.</li>
<li><code>tokens</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object[]></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type"><undefined></a> See <a href="#parseargs-tokens">parseArgs tokens</a>
section. Only returned if <code>config</code> includes <code>tokens: true</code>.</li>
</ul>
</li>
</ul>
<p>Provides a higher level API for command-line argument parsing than interacting
with <code>process.argv</code> directly. Takes a specification for the expected arguments
and returns a structured object with the parsed options and positionals.</p>
<pre class="with-43-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> { parseArgs } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:util'</span>;
<span class="hljs-keyword">const</span> args = [<span class="hljs-string">'-f'</span>, <span class="hljs-string">'--bar'</span>, <span class="hljs-string">'b'</span>];
<span class="hljs-keyword">const</span> options = {
<span class="hljs-attr">foo</span>: {
<span class="hljs-attr">type</span>: <span class="hljs-string">'boolean'</span>,
<span class="hljs-attr">short</span>: <span class="hljs-string">'f'</span>,
},
<span class="hljs-attr">bar</span>: {
<span class="hljs-attr">type</span>: <span class="hljs-string">'string'</span>,
},
};
<span class="hljs-keyword">const</span> {
values,
positionals,
} = <span class="hljs-title function_">parseArgs</span>({ args, options });
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(values, positionals);
<span class="hljs-comment">// Prints: [Object: null prototype] { foo: true, bar: 'b' } []</span></code><code class="language-js cjs"><span class="hljs-keyword">const</span> { parseArgs } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);
<span class="hljs-keyword">const</span> args = [<span class="hljs-string">'-f'</span>, <span class="hljs-string">'--bar'</span>, <span class="hljs-string">'b'</span>];
<span class="hljs-keyword">const</span> options = {
<span class="hljs-attr">foo</span>: {
<span class="hljs-attr">type</span>: <span class="hljs-string">'boolean'</span>,
<span class="hljs-attr">short</span>: <span class="hljs-string">'f'</span>,
},
<span class="hljs-attr">bar</span>: {
<span class="hljs-attr">type</span>: <span class="hljs-string">'string'</span>,
},
};
<span class="hljs-keyword">const</span> {
values,
positionals,
} = <span class="hljs-title function_">parseArgs</span>({ args, options });
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(values, positionals);
<span class="hljs-comment">// Prints: [Object: null prototype] { foo: true, bar: 'b' } []</span></code><button class="copy-button">copy</button></pre>
<h4><code>parseArgs</code> <code>tokens</code><span><a class="mark" href="#parseargs-tokens" id="parseargs-tokens">#</a></span><a aria-hidden="true" class="legacy" id="util_parseargs_tokens"></a></h4>
<p>Detailed parse information is available for adding custom behaviors by
specifying <code>tokens: true</code> in the configuration.
The returned tokens have properties describing:</p>
<ul>
<li>all tokens
<ul>
<li><code>kind</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> One of 'option', 'positional', or 'option-terminator'.</li>
<li><code>index</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> Index of element in <code>args</code> containing token. So the
source argument for a token is <code>args[token.index]</code>.</li>
</ul>
</li>
<li>option tokens
<ul>
<li><code>name</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> Long name of option.</li>
<li><code>rawName</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> How option used in args, like <code>-f</code> of <code>--foo</code>.</li>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type"><undefined></a> Option value specified in args.
Undefined for boolean options.</li>
<li><code>inlineValue</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type"><undefined></a> Whether option value specified inline,
like <code>--foo=bar</code>.</li>
</ul>
</li>
<li>positional tokens
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> The value of the positional argument in args (i.e. <code>args[index]</code>).</li>
</ul>
</li>
<li>option-terminator token</li>
</ul>
<p>The returned tokens are in the order encountered in the input args. Options
that appear more than once in args produce a token for each use. Short option
groups like <code>-xy</code> expand to a token for each option. So <code>-xxx</code> produces
three tokens.</p>
<p>For example to use the returned tokens to add support for a negated option
like <code>--no-color</code>, the tokens can be reprocessed to change the value stored
for the negated option.</p>
<pre class="with-43-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> { parseArgs } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:util'</span>;
<span class="hljs-keyword">const</span> options = {
<span class="hljs-string">'color'</span>: { <span class="hljs-attr">type</span>: <span class="hljs-string">'boolean'</span> },
<span class="hljs-string">'no-color'</span>: { <span class="hljs-attr">type</span>: <span class="hljs-string">'boolean'</span> },
<span class="hljs-string">'logfile'</span>: { <span class="hljs-attr">type</span>: <span class="hljs-string">'string'</span> },
<span class="hljs-string">'no-logfile'</span>: { <span class="hljs-attr">type</span>: <span class="hljs-string">'boolean'</span> },
};
<span class="hljs-keyword">const</span> { values, tokens } = <span class="hljs-title function_">parseArgs</span>({ options, <span class="hljs-attr">tokens</span>: <span class="hljs-literal">true</span> });
<span class="hljs-comment">// Reprocess the option tokens and overwrite the returned values.</span>
tokens
.<span class="hljs-title function_">filter</span>(<span class="hljs-function">(<span class="hljs-params">token</span>) =></span> token.<span class="hljs-property">kind</span> === <span class="hljs-string">'option'</span>)
.<span class="hljs-title function_">forEach</span>(<span class="hljs-function">(<span class="hljs-params">token</span>) =></span> {
<span class="hljs-keyword">if</span> (token.<span class="hljs-property">name</span>.<span class="hljs-title function_">startsWith</span>(<span class="hljs-string">'no-'</span>)) {
<span class="hljs-comment">// Store foo:false for --no-foo</span>
<span class="hljs-keyword">const</span> positiveName = token.<span class="hljs-property">name</span>.<span class="hljs-title function_">slice</span>(<span class="hljs-number">3</span>);
values[positiveName] = <span class="hljs-literal">false</span>;
<span class="hljs-keyword">delete</span> values[token.<span class="hljs-property">name</span>];
} <span class="hljs-keyword">else</span> {
<span class="hljs-comment">// Resave value so last one wins if both --foo and --no-foo.</span>
values[token.<span class="hljs-property">name</span>] = token.<span class="hljs-property">value</span> ?? <span class="hljs-literal">true</span>;
}
});
<span class="hljs-keyword">const</span> color = values.<span class="hljs-property">color</span>;
<span class="hljs-keyword">const</span> logfile = values.<span class="hljs-property">logfile</span> ?? <span class="hljs-string">'default.log'</span>;
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>({ logfile, color });</code><code class="language-js cjs"><span class="hljs-keyword">const</span> { parseArgs } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);
<span class="hljs-keyword">const</span> options = {
<span class="hljs-string">'color'</span>: { <span class="hljs-attr">type</span>: <span class="hljs-string">'boolean'</span> },
<span class="hljs-string">'no-color'</span>: { <span class="hljs-attr">type</span>: <span class="hljs-string">'boolean'</span> },
<span class="hljs-string">'logfile'</span>: { <span class="hljs-attr">type</span>: <span class="hljs-string">'string'</span> },
<span class="hljs-string">'no-logfile'</span>: { <span class="hljs-attr">type</span>: <span class="hljs-string">'boolean'</span> },
};
<span class="hljs-keyword">const</span> { values, tokens } = <span class="hljs-title function_">parseArgs</span>({ options, <span class="hljs-attr">tokens</span>: <span class="hljs-literal">true</span> });
<span class="hljs-comment">// Reprocess the option tokens and overwrite the returned values.</span>
tokens
.<span class="hljs-title function_">filter</span>(<span class="hljs-function">(<span class="hljs-params">token</span>) =></span> token.<span class="hljs-property">kind</span> === <span class="hljs-string">'option'</span>)
.<span class="hljs-title function_">forEach</span>(<span class="hljs-function">(<span class="hljs-params">token</span>) =></span> {
<span class="hljs-keyword">if</span> (token.<span class="hljs-property">name</span>.<span class="hljs-title function_">startsWith</span>(<span class="hljs-string">'no-'</span>)) {
<span class="hljs-comment">// Store foo:false for --no-foo</span>
<span class="hljs-keyword">const</span> positiveName = token.<span class="hljs-property">name</span>.<span class="hljs-title function_">slice</span>(<span class="hljs-number">3</span>);
values[positiveName] = <span class="hljs-literal">false</span>;
<span class="hljs-keyword">delete</span> values[token.<span class="hljs-property">name</span>];
} <span class="hljs-keyword">else</span> {
<span class="hljs-comment">// Resave value so last one wins if both --foo and --no-foo.</span>
values[token.<span class="hljs-property">name</span>] = token.<span class="hljs-property">value</span> ?? <span class="hljs-literal">true</span>;
}
});
<span class="hljs-keyword">const</span> color = values.<span class="hljs-property">color</span>;
<span class="hljs-keyword">const</span> logfile = values.<span class="hljs-property">logfile</span> ?? <span class="hljs-string">'default.log'</span>;
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>({ logfile, color });</code><button class="copy-button">copy</button></pre>
<p>Example usage showing negated options, and when an option is used
multiple ways then last one wins.</p>
<pre><code class="language-console"><span class="hljs-meta prompt_">$ </span><span class="language-bash">node negate.js</span>
{ logfile: 'default.log', color: undefined }
<span class="hljs-meta prompt_">$ </span><span class="language-bash">node negate.js --no-logfile --no-color</span>
{ logfile: false, color: false }
<span class="hljs-meta prompt_">$ </span><span class="language-bash">node negate.js --logfile=test.log --color</span>
{ logfile: 'test.log', color: true }
<span class="hljs-meta prompt_">$ </span><span class="language-bash">node negate.js --no-logfile --logfile=test.log --color --no-color</span>
{ logfile: 'test.log', color: false }</code> <button class="copy-button">copy</button></pre>
</section><section><h3><code>util.parseEnv(content)</code><span><a class="mark" href="#utilparseenvcontent" id="utilparseenvcontent">#</a></span><a aria-hidden="true" class="legacy" id="util_util_parseenv_content"></a></h3>
<p></p><div class="api_stability api_stability_1"><a href="documentation.html#stability-index">Stability: 1</a>.1 - Active development</div><p></p>
<div class="api_metadata">
<span>Added in: v20.12.0</span>
</div>
<ul>
<li><code>content</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li>
</ul>
<p>The raw contents of a <code>.env</code> file.</p>
<ul>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li>
</ul>
<p>Given an example <code>.env</code> file:</p>
<pre class="with-42-chars"><input class="js-flavor-toggle" type="checkbox" aria-label="Show modern ES modules syntax"><code class="language-js cjs"><span class="hljs-keyword">const</span> { parseEnv } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);
<span class="hljs-title function_">parseEnv</span>(<span class="hljs-string">'HELLO=world\nHELLO=oh my\n'</span>);
<span class="hljs-comment">// Returns: { HELLO: 'oh my' }</span></code><code class="language-js mjs"><span class="hljs-keyword">import</span> { parseEnv } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:util'</span>;
<span class="hljs-title function_">parseEnv</span>(<span class="hljs-string">'HELLO=world\nHELLO=oh my\n'</span>);
<span class="hljs-comment">// Returns: { HELLO: 'oh my' }</span></code><button class="copy-button">copy</button></pre>
</section><section><h3><code>util.promisify(original)</code><span><a class="mark" href="#utilpromisifyoriginal" id="utilpromisifyoriginal">#</a></span><a aria-hidden="true" class="legacy" id="util_util_promisify_original"></a></h3>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v20.8.0</td>
<td><p>Calling <code>promisify</code> on a function that returns a <code>Promise</code> is deprecated.</p></td></tr>
<tr><td>v8.0.0</td>
<td><p><span>Added in: v8.0.0</span></p></td></tr>
</tbody></table>
</details>
</div>
<ul>
<li><code>original</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></li>
</ul>
<p>Takes a function following the common error-first callback style, i.e. taking
an <code>(err, value) => ...</code> callback as the last argument, and returns a version
that returns promises.</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);
<span class="hljs-keyword">const</span> fs = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:fs'</span>);
<span class="hljs-keyword">const</span> stat = util.<span class="hljs-title function_">promisify</span>(fs.<span class="hljs-property">stat</span>);
<span class="hljs-title function_">stat</span>(<span class="hljs-string">'.'</span>).<span class="hljs-title function_">then</span>(<span class="hljs-function">(<span class="hljs-params">stats</span>) =></span> {
<span class="hljs-comment">// Do something with `stats`</span>
}).<span class="hljs-title function_">catch</span>(<span class="hljs-function">(<span class="hljs-params">error</span>) =></span> {
<span class="hljs-comment">// Handle the error.</span>
});</code> <button class="copy-button">copy</button></pre>
<p>Or, equivalently using <code>async function</code>s:</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);
<span class="hljs-keyword">const</span> fs = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:fs'</span>);
<span class="hljs-keyword">const</span> stat = util.<span class="hljs-title function_">promisify</span>(fs.<span class="hljs-property">stat</span>);
<span class="hljs-keyword">async</span> <span class="hljs-keyword">function</span> <span class="hljs-title function_">callStat</span>(<span class="hljs-params"></span>) {
<span class="hljs-keyword">const</span> stats = <span class="hljs-keyword">await</span> <span class="hljs-title function_">stat</span>(<span class="hljs-string">'.'</span>);
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">`This directory is owned by <span class="hljs-subst">${stats.uid}</span>`</span>);
}
<span class="hljs-title function_">callStat</span>();</code> <button class="copy-button">copy</button></pre>
<p>If there is an <code>original[util.promisify.custom]</code> property present, <code>promisify</code>
will return its value, see <a href="#custom-promisified-functions">Custom promisified functions</a>.</p>
<p><code>promisify()</code> assumes that <code>original</code> is a function taking a callback as its
final argument in all cases. If <code>original</code> is not a function, <code>promisify()</code>
will throw an error. If <code>original</code> is a function but its last argument is not
an error-first callback, it will still be passed an error-first
callback as its last argument.</p>
<p>Using <code>promisify()</code> on class methods or other methods that use <code>this</code> may not
work as expected unless handled specially:</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);
<span class="hljs-keyword">class</span> <span class="hljs-title class_">Foo</span> {
<span class="hljs-title function_">constructor</span>(<span class="hljs-params"></span>) {
<span class="hljs-variable language_">this</span>.<span class="hljs-property">a</span> = <span class="hljs-number">42</span>;
}
<span class="hljs-title function_">bar</span>(<span class="hljs-params">callback</span>) {
<span class="hljs-title function_">callback</span>(<span class="hljs-literal">null</span>, <span class="hljs-variable language_">this</span>.<span class="hljs-property">a</span>);
}
}
<span class="hljs-keyword">const</span> foo = <span class="hljs-keyword">new</span> <span class="hljs-title class_">Foo</span>();
<span class="hljs-keyword">const</span> naiveBar = util.<span class="hljs-title function_">promisify</span>(foo.<span class="hljs-property">bar</span>);
<span class="hljs-comment">// TypeError: Cannot read property 'a' of undefined</span>
<span class="hljs-comment">// naiveBar().then(a => console.log(a));</span>
naiveBar.<span class="hljs-title function_">call</span>(foo).<span class="hljs-title function_">then</span>(<span class="hljs-function">(<span class="hljs-params">a</span>) =></span> <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(a)); <span class="hljs-comment">// '42'</span>
<span class="hljs-keyword">const</span> bindBar = naiveBar.<span class="hljs-title function_">bind</span>(foo);
<span class="hljs-title function_">bindBar</span>().<span class="hljs-title function_">then</span>(<span class="hljs-function">(<span class="hljs-params">a</span>) =></span> <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(a)); <span class="hljs-comment">// '42'</span></code> <button class="copy-button">copy</button></pre>
<h4>Custom promisified functions<span><a class="mark" href="#custom-promisified-functions" id="custom-promisified-functions">#</a></span><a aria-hidden="true" class="legacy" id="util_custom_promisified_functions"></a></h4>
<p>Using the <code>util.promisify.custom</code> symbol one can override the return value of
<a href="#utilpromisifyoriginal"><code>util.promisify()</code></a>:</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);
<span class="hljs-keyword">function</span> <span class="hljs-title function_">doSomething</span>(<span class="hljs-params">foo, callback</span>) {
<span class="hljs-comment">// ...</span>
}
doSomething[util.<span class="hljs-property">promisify</span>.<span class="hljs-property">custom</span>] = <span class="hljs-function">(<span class="hljs-params">foo</span>) =></span> {
<span class="hljs-keyword">return</span> <span class="hljs-title function_">getPromiseSomehow</span>();
};
<span class="hljs-keyword">const</span> promisified = util.<span class="hljs-title function_">promisify</span>(doSomething);
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(promisified === doSomething[util.<span class="hljs-property">promisify</span>.<span class="hljs-property">custom</span>]);
<span class="hljs-comment">// prints 'true'</span></code> <button class="copy-button">copy</button></pre>
<p>This can be useful for cases where the original function does not follow the
standard format of taking an error-first callback as the last argument.</p>
<p>For example, with a function that takes in
<code>(foo, onSuccessCallback, onErrorCallback)</code>:</p>
<pre><code class="language-js">doSomething[util.<span class="hljs-property">promisify</span>.<span class="hljs-property">custom</span>] = <span class="hljs-function">(<span class="hljs-params">foo</span>) =></span> {
<span class="hljs-keyword">return</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">Promise</span>(<span class="hljs-function">(<span class="hljs-params">resolve, reject</span>) =></span> {
<span class="hljs-title function_">doSomething</span>(foo, resolve, reject);
});
};</code> <button class="copy-button">copy</button></pre>
<p>If <code>promisify.custom</code> is defined but is not a function, <code>promisify()</code> will
throw an error.</p>
<h4><code>util.promisify.custom</code><span><a class="mark" href="#utilpromisifycustom" id="utilpromisifycustom">#</a></span><a aria-hidden="true" class="legacy" id="util_util_promisify_custom"></a></h4>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v13.12.0, v12.16.2</td>
<td><p>This is now defined as a shared symbol.</p></td></tr>
<tr><td>v8.0.0</td>
<td><p><span>Added in: v8.0.0</span></p></td></tr>
</tbody></table>
</details>
</div>
<ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Symbol_type" class="type"><symbol></a> that can be used to declare custom promisified variants of functions,
see <a href="#custom-promisified-functions">Custom promisified functions</a>.</li>
</ul>
<p>In addition to being accessible through <code>util.promisify.custom</code>, this
symbol is <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol/for">registered globally</a> and can be
accessed in any environment as <code>Symbol.for('nodejs.util.promisify.custom')</code>.</p>
<p>For example, with a function that takes in
<code>(foo, onSuccessCallback, onErrorCallback)</code>:</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> kCustomPromisifiedSymbol = <span class="hljs-title class_">Symbol</span>.<span class="hljs-title function_">for</span>(<span class="hljs-string">'nodejs.util.promisify.custom'</span>);
doSomething[kCustomPromisifiedSymbol] = <span class="hljs-function">(<span class="hljs-params">foo</span>) =></span> {
<span class="hljs-keyword">return</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">Promise</span>(<span class="hljs-function">(<span class="hljs-params">resolve, reject</span>) =></span> {
<span class="hljs-title function_">doSomething</span>(foo, resolve, reject);
});
};</code> <button class="copy-button">copy</button></pre>
</section><section><h3><code>util.stripVTControlCharacters(str)</code><span><a class="mark" href="#utilstripvtcontrolcharactersstr" id="utilstripvtcontrolcharactersstr">#</a></span><a aria-hidden="true" class="legacy" id="util_util_stripvtcontrolcharacters_str"></a></h3>
<div class="api_metadata">
<span>Added in: v16.11.0</span>
</div>
<ul>
<li><code>str</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li>
</ul>
<p>Returns <code>str</code> with any ANSI escape codes removed.</p>
<pre><code class="language-js"><span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(util.<span class="hljs-title function_">stripVTControlCharacters</span>(<span class="hljs-string">'\u001B[4mvalue\u001B[0m'</span>));
<span class="hljs-comment">// Prints "value"</span></code> <button class="copy-button">copy</button></pre>
</section><section><h3><code>util.styleText(format, text)</code><span><a class="mark" href="#utilstyletextformat-text" id="utilstyletextformat-text">#</a></span><a aria-hidden="true" class="legacy" id="util_util_styletext_format_text"></a></h3>
<p></p><div class="api_stability api_stability_1"><a href="documentation.html#stability-index">Stability: 1</a>.1 - Active development</div><p></p>
<div class="api_metadata">
<span>Added in: v20.12.0</span>
</div>
<ul>
<li><code>format</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array" class="type"><Array></a> A text format or an Array
of text formats defined in <code>util.inspect.colors</code>.</li>
<li><code>text</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> The text to to be formatted.</li>
</ul>
<p>This function returns a formatted text considering the <code>format</code> passed.</p>
<pre class="with-55-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> { styleText } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:util'</span>;
<span class="hljs-keyword">const</span> errorMessage = <span class="hljs-title function_">styleText</span>(<span class="hljs-string">'red'</span>, <span class="hljs-string">'Error! Error!'</span>);
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(errorMessage);</code><code class="language-js cjs"><span class="hljs-keyword">const</span> { styleText } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);
<span class="hljs-keyword">const</span> errorMessage = <span class="hljs-title function_">styleText</span>(<span class="hljs-string">'red'</span>, <span class="hljs-string">'Error! Error!'</span>);
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(errorMessage);</code><button class="copy-button">copy</button></pre>
<p><code>util.inspect.colors</code> also provides text formats such as <code>italic</code>, and
<code>underline</code> and you can combine both:</p>
<pre><code class="language-js cjs"><span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(
util.<span class="hljs-title function_">styleText</span>([<span class="hljs-string">'underline'</span>, <span class="hljs-string">'italic'</span>], <span class="hljs-string">'My italic underlined message'</span>),
);</code> <button class="copy-button">copy</button></pre>
<p>When passing an array of formats, the order of the format applied
is left to right so the following style might overwrite the previous one.</p>
<pre><code class="language-js cjs"><span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(
util.<span class="hljs-title function_">styleText</span>([<span class="hljs-string">'red'</span>, <span class="hljs-string">'green'</span>], <span class="hljs-string">'text'</span>), <span class="hljs-comment">// green</span>
);</code> <button class="copy-button">copy</button></pre>
<p>The full list of formats can be found in <a href="#modifiers">modifiers</a>.</p>
</section><section><h3>Class: <code>util.TextDecoder</code><span><a class="mark" href="#class-utiltextdecoder" id="class-utiltextdecoder">#</a></span><a aria-hidden="true" class="legacy" id="util_class_util_textdecoder"></a></h3>
<div class="api_metadata">
<span>Added in: v8.3.0</span>
</div>
<p>An implementation of the <a href="https://encoding.spec.whatwg.org/">WHATWG Encoding Standard</a> <code>TextDecoder</code> API.</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> decoder = <span class="hljs-keyword">new</span> <span class="hljs-title class_">TextDecoder</span>();
<span class="hljs-keyword">const</span> u8arr = <span class="hljs-keyword">new</span> <span class="hljs-title class_">Uint8Array</span>([<span class="hljs-number">72</span>, <span class="hljs-number">101</span>, <span class="hljs-number">108</span>, <span class="hljs-number">108</span>, <span class="hljs-number">111</span>]);
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(decoder.<span class="hljs-title function_">decode</span>(u8arr)); <span class="hljs-comment">// Hello</span></code> <button class="copy-button">copy</button></pre>
<h4>WHATWG supported encodings<span><a class="mark" href="#whatwg-supported-encodings" id="whatwg-supported-encodings">#</a></span><a aria-hidden="true" class="legacy" id="util_whatwg_supported_encodings"></a></h4>
<p>Per the <a href="https://encoding.spec.whatwg.org/">WHATWG Encoding Standard</a>, the encodings supported by the
<code>TextDecoder</code> API are outlined in the tables below. For each encoding,
one or more aliases may be used.</p>
<p>Different Node.js build configurations support different sets of encodings.
(see <a href="intl.html">Internationalization</a>)</p>
<h5>Encodings supported by default (with full ICU data)<span><a class="mark" href="#encodings-supported-by-default-with-full-icu-data" id="encodings-supported-by-default-with-full-icu-data">#</a></span><a aria-hidden="true" class="legacy" id="util_encodings_supported_by_default_with_full_icu_data"></a></h5>
<table><thead><tr><th>Encoding</th><th>Aliases</th></tr></thead><tbody><tr><td><code>'ibm866'</code></td><td><code>'866'</code>, <code>'cp866'</code>, <code>'csibm866'</code></td></tr><tr><td><code>'iso-8859-2'</code></td><td><code>'csisolatin2'</code>, <code>'iso-ir-101'</code>, <code>'iso8859-2'</code>, <code>'iso88592'</code>, <code>'iso_8859-2'</code>, <code>'iso_8859-2:1987'</code>, <code>'l2'</code>, <code>'latin2'</code></td></tr><tr><td><code>'iso-8859-3'</code></td><td><code>'csisolatin3'</code>, <code>'iso-ir-109'</code>, <code>'iso8859-3'</code>, <code>'iso88593'</code>, <code>'iso_8859-3'</code>, <code>'iso_8859-3:1988'</code>, <code>'l3'</code>, <code>'latin3'</code></td></tr><tr><td><code>'iso-8859-4'</code></td><td><code>'csisolatin4'</code>, <code>'iso-ir-110'</code>, <code>'iso8859-4'</code>, <code>'iso88594'</code>, <code>'iso_8859-4'</code>, <code>'iso_8859-4:1988'</code>, <code>'l4'</code>, <code>'latin4'</code></td></tr><tr><td><code>'iso-8859-5'</code></td><td><code>'csisolatincyrillic'</code>, <code>'cyrillic'</code>, <code>'iso-ir-144'</code>, <code>'iso8859-5'</code>, <code>'iso88595'</code>, <code>'iso_8859-5'</code>, <code>'iso_8859-5:1988'</code></td></tr><tr><td><code>'iso-8859-6'</code></td><td><code>'arabic'</code>, <code>'asmo-708'</code>, <code>'csiso88596e'</code>, <code>'csiso88596i'</code>, <code>'csisolatinarabic'</code>, <code>'ecma-114'</code>, <code>'iso-8859-6-e'</code>, <code>'iso-8859-6-i'</code>, <code>'iso-ir-127'</code>, <code>'iso8859-6'</code>, <code>'iso88596'</code>, <code>'iso_8859-6'</code>, <code>'iso_8859-6:1987'</code></td></tr><tr><td><code>'iso-8859-7'</code></td><td><code>'csisolatingreek'</code>, <code>'ecma-118'</code>, <code>'elot_928'</code>, <code>'greek'</code>, <code>'greek8'</code>, <code>'iso-ir-126'</code>, <code>'iso8859-7'</code>, <code>'iso88597'</code>, <code>'iso_8859-7'</code>, <code>'iso_8859-7:1987'</code>, <code>'sun_eu_greek'</code></td></tr><tr><td><code>'iso-8859-8'</code></td><td><code>'csiso88598e'</code>, <code>'csisolatinhebrew'</code>, <code>'hebrew'</code>, <code>'iso-8859-8-e'</code>, <code>'iso-ir-138'</code>, <code>'iso8859-8'</code>, <code>'iso88598'</code>, <code>'iso_8859-8'</code>, <code>'iso_8859-8:1988'</code>, <code>'visual'</code></td></tr><tr><td><code>'iso-8859-8-i'</code></td><td><code>'csiso88598i'</code>, <code>'logical'</code></td></tr><tr><td><code>'iso-8859-10'</code></td><td><code>'csisolatin6'</code>, <code>'iso-ir-157'</code>, <code>'iso8859-10'</code>, <code>'iso885910'</code>, <code>'l6'</code>, <code>'latin6'</code></td></tr><tr><td><code>'iso-8859-13'</code></td><td><code>'iso8859-13'</code>, <code>'iso885913'</code></td></tr><tr><td><code>'iso-8859-14'</code></td><td><code>'iso8859-14'</code>, <code>'iso885914'</code></td></tr><tr><td><code>'iso-8859-15'</code></td><td><code>'csisolatin9'</code>, <code>'iso8859-15'</code>, <code>'iso885915'</code>, <code>'iso_8859-15'</code>, <code>'l9'</code></td></tr><tr><td><code>'koi8-r'</code></td><td><code>'cskoi8r'</code>, <code>'koi'</code>, <code>'koi8'</code>, <code>'koi8_r'</code></td></tr><tr><td><code>'koi8-u'</code></td><td><code>'koi8-ru'</code></td></tr><tr><td><code>'macintosh'</code></td><td><code>'csmacintosh'</code>, <code>'mac'</code>, <code>'x-mac-roman'</code></td></tr><tr><td><code>'windows-874'</code></td><td><code>'dos-874'</code>, <code>'iso-8859-11'</code>, <code>'iso8859-11'</code>, <code>'iso885911'</code>, <code>'tis-620'</code></td></tr><tr><td><code>'windows-1250'</code></td><td><code>'cp1250'</code>, <code>'x-cp1250'</code></td></tr><tr><td><code>'windows-1251'</code></td><td><code>'cp1251'</code>, <code>'x-cp1251'</code></td></tr><tr><td><code>'windows-1252'</code></td><td><code>'ansi_x3.4-1968'</code>, <code>'ascii'</code>, <code>'cp1252'</code>, <code>'cp819'</code>, <code>'csisolatin1'</code>, <code>'ibm819'</code>, <code>'iso-8859-1'</code>, <code>'iso-ir-100'</code>, <code>'iso8859-1'</code>, <code>'iso88591'</code>, <code>'iso_8859-1'</code>, <code>'iso_8859-1:1987'</code>, <code>'l1'</code>, <code>'latin1'</code>, <code>'us-ascii'</code>, <code>'x-cp1252'</code></td></tr><tr><td><code>'windows-1253'</code></td><td><code>'cp1253'</code>, <code>'x-cp1253'</code></td></tr><tr><td><code>'windows-1254'</code></td><td><code>'cp1254'</code>, <code>'csisolatin5'</code>, <code>'iso-8859-9'</code>, <code>'iso-ir-148'</code>, <code>'iso8859-9'</code>, <code>'iso88599'</code>, <code>'iso_8859-9'</code>, <code>'iso_8859-9:1989'</code>, <code>'l5'</code>, <code>'latin5'</code>, <code>'x-cp1254'</code></td></tr><tr><td><code>'windows-1255'</code></td><td><code>'cp1255'</code>, <code>'x-cp1255'</code></td></tr><tr><td><code>'windows-1256'</code></td><td><code>'cp1256'</code>, <code>'x-cp1256'</code></td></tr><tr><td><code>'windows-1257'</code></td><td><code>'cp1257'</code>, <code>'x-cp1257'</code></td></tr><tr><td><code>'windows-1258'</code></td><td><code>'cp1258'</code>, <code>'x-cp1258'</code></td></tr><tr><td><code>'x-mac-cyrillic'</code></td><td><code>'x-mac-ukrainian'</code></td></tr><tr><td><code>'gbk'</code></td><td><code>'chinese'</code>, <code>'csgb2312'</code>, <code>'csiso58gb231280'</code>, <code>'gb2312'</code>, <code>'gb_2312'</code>, <code>'gb_2312-80'</code>, <code>'iso-ir-58'</code>, <code>'x-gbk'</code></td></tr><tr><td><code>'gb18030'</code></td><td></td></tr><tr><td><code>'big5'</code></td><td><code>'big5-hkscs'</code>, <code>'cn-big5'</code>, <code>'csbig5'</code>, <code>'x-x-big5'</code></td></tr><tr><td><code>'euc-jp'</code></td><td><code>'cseucpkdfmtjapanese'</code>, <code>'x-euc-jp'</code></td></tr><tr><td><code>'iso-2022-jp'</code></td><td><code>'csiso2022jp'</code></td></tr><tr><td><code>'shift_jis'</code></td><td><code>'csshiftjis'</code>, <code>'ms932'</code>, <code>'ms_kanji'</code>, <code>'shift-jis'</code>, <code>'sjis'</code>, <code>'windows-31j'</code>, <code>'x-sjis'</code></td></tr><tr><td><code>'euc-kr'</code></td><td><code>'cseuckr'</code>, <code>'csksc56011987'</code>, <code>'iso-ir-149'</code>, <code>'korean'</code>, <code>'ks_c_5601-1987'</code>, <code>'ks_c_5601-1989'</code>, <code>'ksc5601'</code>, <code>'ksc_5601'</code>, <code>'windows-949'</code></td></tr></tbody></table>
<h5>Encodings supported when Node.js is built with the <code>small-icu</code> option<span><a class="mark" href="#encodings-supported-when-nodejs-is-built-with-the-small-icu-option" id="encodings-supported-when-nodejs-is-built-with-the-small-icu-option">#</a></span><a aria-hidden="true" class="legacy" id="util_encodings_supported_when_node_js_is_built_with_the_small_icu_option"></a></h5>
<table><thead><tr><th>Encoding</th><th>Aliases</th></tr></thead><tbody><tr><td><code>'utf-8'</code></td><td><code>'unicode-1-1-utf-8'</code>, <code>'utf8'</code></td></tr><tr><td><code>'utf-16le'</code></td><td><code>'utf-16'</code></td></tr><tr><td><code>'utf-16be'</code></td><td></td></tr></tbody></table>
<h5>Encodings supported when ICU is disabled<span><a class="mark" href="#encodings-supported-when-icu-is-disabled" id="encodings-supported-when-icu-is-disabled">#</a></span><a aria-hidden="true" class="legacy" id="util_encodings_supported_when_icu_is_disabled"></a></h5>
<table><thead><tr><th>Encoding</th><th>Aliases</th></tr></thead><tbody><tr><td><code>'utf-8'</code></td><td><code>'unicode-1-1-utf-8'</code>, <code>'utf8'</code></td></tr><tr><td><code>'utf-16le'</code></td><td><code>'utf-16'</code></td></tr></tbody></table>
<p>The <code>'iso-8859-16'</code> encoding listed in the <a href="https://encoding.spec.whatwg.org/">WHATWG Encoding Standard</a>
is not supported.</p>
<h4><code>new TextDecoder([encoding[, options]])</code><span><a class="mark" href="#new-textdecoderencoding-options" id="new-textdecoderencoding-options">#</a></span><a aria-hidden="true" class="legacy" id="util_new_textdecoder_encoding_options"></a></h4>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v11.0.0</td>
<td><p>The class is now available on the global object.</p></td></tr>
<tr><td>v8.3.0</td>
<td><p><span>Added in: v8.3.0</span></p></td></tr>
</tbody></table>
</details>
</div>
<ul>
<li><code>encoding</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> Identifies the <code>encoding</code> that this <code>TextDecoder</code> instance
supports. <strong>Default:</strong> <code>'utf-8'</code>.</li>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a>
<ul>
<li><code>fatal</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> <code>true</code> if decoding failures are fatal.
This option is not supported when ICU is disabled
(see <a href="intl.html">Internationalization</a>). <strong>Default:</strong> <code>false</code>.</li>
<li><code>ignoreBOM</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> When <code>true</code>, the <code>TextDecoder</code> will include the byte
order mark in the decoded result. When <code>false</code>, the byte order mark will
be removed from the output. This option is only used when <code>encoding</code> is
<code>'utf-8'</code>, <code>'utf-16be'</code>, or <code>'utf-16le'</code>. <strong>Default:</strong> <code>false</code>.</li>
</ul>
</li>
</ul>
<p>Creates a new <code>TextDecoder</code> instance. The <code>encoding</code> may specify one of the
supported encodings or an alias.</p>
<p>The <code>TextDecoder</code> class is also available on the global object.</p>
<h4><code>textDecoder.decode([input[, options]])</code><span><a class="mark" href="#textdecoderdecodeinput-options" id="textdecoderdecodeinput-options">#</a></span><a aria-hidden="true" class="legacy" id="util_textdecoder_decode_input_options"></a></h4>
<ul>
<li><code>input</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer" class="type"><ArrayBuffer></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView" class="type"><DataView></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray" class="type"><TypedArray></a> An <code>ArrayBuffer</code>, <code>DataView</code>, or
<code>TypedArray</code> instance containing the encoded data.</li>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a>
<ul>
<li><code>stream</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> <code>true</code> if additional chunks of data are expected.
<strong>Default:</strong> <code>false</code>.</li>
</ul>
</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li>
</ul>
<p>Decodes the <code>input</code> and returns a string. If <code>options.stream</code> is <code>true</code>, any
incomplete byte sequences occurring at the end of the <code>input</code> are buffered
internally and emitted after the next call to <code>textDecoder.decode()</code>.</p>
<p>If <code>textDecoder.fatal</code> is <code>true</code>, decoding errors that occur will result in a
<code>TypeError</code> being thrown.</p>
<h4><code>textDecoder.encoding</code><span><a class="mark" href="#textdecoderencoding" id="textdecoderencoding">#</a></span><a aria-hidden="true" class="legacy" id="util_textdecoder_encoding"></a></h4>
<ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li>
</ul>
<p>The encoding supported by the <code>TextDecoder</code> instance.</p>
<h4><code>textDecoder.fatal</code><span><a class="mark" href="#textdecoderfatal" id="textdecoderfatal">#</a></span><a aria-hidden="true" class="legacy" id="util_textdecoder_fatal"></a></h4>
<ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>The value will be <code>true</code> if decoding errors result in a <code>TypeError</code> being
thrown.</p>
<h4><code>textDecoder.ignoreBOM</code><span><a class="mark" href="#textdecoderignorebom" id="textdecoderignorebom">#</a></span><a aria-hidden="true" class="legacy" id="util_textdecoder_ignorebom"></a></h4>
<ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>The value will be <code>true</code> if the decoding result will include the byte order
mark.</p>
</section><section><h3>Class: <code>util.TextEncoder</code><span><a class="mark" href="#class-utiltextencoder" id="class-utiltextencoder">#</a></span><a aria-hidden="true" class="legacy" id="util_class_util_textencoder"></a></h3>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v11.0.0</td>
<td><p>The class is now available on the global object.</p></td></tr>
<tr><td>v8.3.0</td>
<td><p><span>Added in: v8.3.0</span></p></td></tr>
</tbody></table>
</details>
</div>
<p>An implementation of the <a href="https://encoding.spec.whatwg.org/">WHATWG Encoding Standard</a> <code>TextEncoder</code> API. All
instances of <code>TextEncoder</code> only support UTF-8 encoding.</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> encoder = <span class="hljs-keyword">new</span> <span class="hljs-title class_">TextEncoder</span>();
<span class="hljs-keyword">const</span> uint8array = encoder.<span class="hljs-title function_">encode</span>(<span class="hljs-string">'this is some data'</span>);</code> <button class="copy-button">copy</button></pre>
<p>The <code>TextEncoder</code> class is also available on the global object.</p>
<h4><code>textEncoder.encode([input])</code><span><a class="mark" href="#textencoderencodeinput" id="textencoderencodeinput">#</a></span><a aria-hidden="true" class="legacy" id="util_textencoder_encode_input"></a></h4>
<ul>
<li><code>input</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> The text to encode. <strong>Default:</strong> an empty string.</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array" class="type"><Uint8Array></a></li>
</ul>
<p>UTF-8 encodes the <code>input</code> string and returns a <code>Uint8Array</code> containing the
encoded bytes.</p>
<h4><code>textEncoder.encodeInto(src, dest)</code><span><a class="mark" href="#textencoderencodeintosrc-dest" id="textencoderencodeintosrc-dest">#</a></span><a aria-hidden="true" class="legacy" id="util_textencoder_encodeinto_src_dest"></a></h4>
<ul>
<li><code>src</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> The text to encode.</li>
<li><code>dest</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array" class="type"><Uint8Array></a> The array to hold the encode result.</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a>
<ul>
<li><code>read</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> The read Unicode code units of src.</li>
<li><code>written</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> The written UTF-8 bytes of dest.</li>
</ul>
</li>
</ul>
<p>UTF-8 encodes the <code>src</code> string to the <code>dest</code> Uint8Array and returns an object
containing the read Unicode code units and written UTF-8 bytes.</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> encoder = <span class="hljs-keyword">new</span> <span class="hljs-title class_">TextEncoder</span>();
<span class="hljs-keyword">const</span> src = <span class="hljs-string">'this is some data'</span>;
<span class="hljs-keyword">const</span> dest = <span class="hljs-keyword">new</span> <span class="hljs-title class_">Uint8Array</span>(<span class="hljs-number">10</span>);
<span class="hljs-keyword">const</span> { read, written } = encoder.<span class="hljs-title function_">encodeInto</span>(src, dest);</code> <button class="copy-button">copy</button></pre>
<h4><code>textEncoder.encoding</code><span><a class="mark" href="#textencoderencoding" id="textencoderencoding">#</a></span><a aria-hidden="true" class="legacy" id="util_textencoder_encoding"></a></h4>
<ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li>
</ul>
<p>The encoding supported by the <code>TextEncoder</code> instance. Always set to <code>'utf-8'</code>.</p>
</section><section><h3><code>util.toUSVString(string)</code><span><a class="mark" href="#utiltousvstringstring" id="utiltousvstringstring">#</a></span><a aria-hidden="true" class="legacy" id="util_util_tousvstring_string"></a></h3>
<div class="api_metadata">
<span>Added in: v16.8.0, v14.18.0</span>
</div>
<ul>
<li><code>string</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li>
</ul>
<p>Returns the <code>string</code> after replacing any surrogate code points
(or equivalently, any unpaired surrogate code units) with the
Unicode "replacement character" U+FFFD.</p>
</section><section><h3><code>util.transferableAbortController()</code><span><a class="mark" href="#utiltransferableabortcontroller" id="utiltransferableabortcontroller">#</a></span><a aria-hidden="true" class="legacy" id="util_util_transferableabortcontroller"></a></h3>
<div class="api_metadata">
<span>Added in: v18.11.0</span>
</div>
<p></p><div class="api_stability api_stability_1"><a href="documentation.html#stability-index">Stability: 1</a> - Experimental</div><p></p>
<p>Creates and returns an <a href="globals.html#class-abortcontroller" class="type"><AbortController></a> instance whose <a href="globals.html#class-abortsignal" class="type"><AbortSignal></a> is marked
as transferable and can be used with <code>structuredClone()</code> or <code>postMessage()</code>.</p>
</section><section><h3><code>util.transferableAbortSignal(signal)</code><span><a class="mark" href="#utiltransferableabortsignalsignal" id="utiltransferableabortsignalsignal">#</a></span><a aria-hidden="true" class="legacy" id="util_util_transferableabortsignal_signal"></a></h3>
<div class="api_metadata">
<span>Added in: v18.11.0</span>
</div>
<p></p><div class="api_stability api_stability_1"><a href="documentation.html#stability-index">Stability: 1</a> - Experimental</div><p></p>
<ul>
<li><code>signal</code> <a href="globals.html#class-abortsignal" class="type"><AbortSignal></a></li>
<li>Returns: <a href="globals.html#class-abortsignal" class="type"><AbortSignal></a></li>
</ul>
<p>Marks the given <a href="globals.html#class-abortsignal" class="type"><AbortSignal></a> as transferable so that it can be used with
<code>structuredClone()</code> and <code>postMessage()</code>.</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> signal = <span class="hljs-title function_">transferableAbortSignal</span>(<span class="hljs-title class_">AbortSignal</span>.<span class="hljs-title function_">timeout</span>(<span class="hljs-number">100</span>));
<span class="hljs-keyword">const</span> channel = <span class="hljs-keyword">new</span> <span class="hljs-title class_">MessageChannel</span>();
channel.<span class="hljs-property">port2</span>.<span class="hljs-title function_">postMessage</span>(signal, [signal]);</code> <button class="copy-button">copy</button></pre>
</section><section><h3><code>util.aborted(signal, resource)</code><span><a class="mark" href="#utilabortedsignal-resource" id="utilabortedsignal-resource">#</a></span><a aria-hidden="true" class="legacy" id="util_util_aborted_signal_resource"></a></h3>
<div class="api_metadata">
<span>Added in: v19.7.0</span>
</div>
<p></p><div class="api_stability api_stability_1"><a href="documentation.html#stability-index">Stability: 1</a> - Experimental</div><p></p>
<ul>
<li><code>signal</code> <a href="globals.html#class-abortsignal" class="type"><AbortSignal></a></li>
<li><code>resource</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> Any non-null entity, reference to which is held weakly.</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise" class="type"><Promise></a></li>
</ul>
<p>Listens to abort event on the provided <code>signal</code> and
returns a promise that is fulfilled when the <code>signal</code> is
aborted. If the passed <code>resource</code> is garbage collected before the <code>signal</code> is
aborted, the returned promise shall remain pending indefinitely.</p>
<pre class="with-41-chars"><input class="js-flavor-toggle" type="checkbox" aria-label="Show modern ES modules syntax"><code class="language-js cjs"><span class="hljs-keyword">const</span> { aborted } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);
<span class="hljs-keyword">const</span> dependent = <span class="hljs-title function_">obtainSomethingAbortable</span>();
<span class="hljs-title function_">aborted</span>(dependent.<span class="hljs-property">signal</span>, dependent).<span class="hljs-title function_">then</span>(<span class="hljs-function">() =></span> {
<span class="hljs-comment">// Do something when dependent is aborted.</span>
});
dependent.<span class="hljs-title function_">on</span>(<span class="hljs-string">'event'</span>, <span class="hljs-function">() =></span> {
dependent.<span class="hljs-title function_">abort</span>();
});</code><code class="language-js mjs"><span class="hljs-keyword">import</span> { aborted } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:util'</span>;
<span class="hljs-keyword">const</span> dependent = <span class="hljs-title function_">obtainSomethingAbortable</span>();
<span class="hljs-title function_">aborted</span>(dependent.<span class="hljs-property">signal</span>, dependent).<span class="hljs-title function_">then</span>(<span class="hljs-function">() =></span> {
<span class="hljs-comment">// Do something when dependent is aborted.</span>
});
dependent.<span class="hljs-title function_">on</span>(<span class="hljs-string">'event'</span>, <span class="hljs-function">() =></span> {
dependent.<span class="hljs-title function_">abort</span>();
});</code><button class="copy-button">copy</button></pre>
</section><section><h3><code>util.types</code><span><a class="mark" href="#utiltypes" id="utiltypes">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types"></a></h3>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v15.3.0</td>
<td><p>Exposed as <code>require('util/types')</code>.</p></td></tr>
<tr><td>v10.0.0</td>
<td><p><span>Added in: v10.0.0</span></p></td></tr>
</tbody></table>
</details>
</div>
<p><code>util.types</code> provides type checks for different kinds of built-in objects.
Unlike <code>instanceof</code> or <code>Object.prototype.toString.call(value)</code>, these checks do
not inspect properties of the object that are accessible from JavaScript (like
their prototype), and usually have the overhead of calling into C++.</p>
<p>The result generally does not make any guarantees about what kinds of
properties or behavior a value exposes in JavaScript. They are primarily
useful for addon developers who prefer to do type checking in JavaScript.</p>
<p>The API is accessible via <code>require('node:util').types</code> or <code>require('node:util/types')</code>.</p>
<h4><code>util.types.isAnyArrayBuffer(value)</code><span><a class="mark" href="#utiltypesisanyarraybuffervalue" id="utiltypesisanyarraybuffervalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isanyarraybuffer_value"></a></h4>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer"><code>ArrayBuffer</code></a> or
<a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer"><code>SharedArrayBuffer</code></a> instance.</p>
<p>See also <a href="#utiltypesisarraybuffervalue"><code>util.types.isArrayBuffer()</code></a> and
<a href="#utiltypesissharedarraybuffervalue"><code>util.types.isSharedArrayBuffer()</code></a>.</p>
<pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isAnyArrayBuffer</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">ArrayBuffer</span>()); <span class="hljs-comment">// Returns true</span>
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isAnyArrayBuffer</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">SharedArrayBuffer</span>()); <span class="hljs-comment">// Returns true</span></code> <button class="copy-button">copy</button></pre>
<h4><code>util.types.isArrayBufferView(value)</code><span><a class="mark" href="#utiltypesisarraybufferviewvalue" id="utiltypesisarraybufferviewvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isarraybufferview_value"></a></h4>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is an instance of one of the <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer"><code>ArrayBuffer</code></a>
views, such as typed array objects or <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView"><code>DataView</code></a>. Equivalent to
<a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer/isView"><code>ArrayBuffer.isView()</code></a>.</p>
<pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isArrayBufferView</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Int8Array</span>()); <span class="hljs-comment">// true</span>
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isArrayBufferView</span>(<span class="hljs-title class_">Buffer</span>.<span class="hljs-title function_">from</span>(<span class="hljs-string">'hello world'</span>)); <span class="hljs-comment">// true</span>
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isArrayBufferView</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">DataView</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">ArrayBuffer</span>(<span class="hljs-number">16</span>))); <span class="hljs-comment">// true</span>
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isArrayBufferView</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">ArrayBuffer</span>()); <span class="hljs-comment">// false</span></code> <button class="copy-button">copy</button></pre>
<h4><code>util.types.isArgumentsObject(value)</code><span><a class="mark" href="#utiltypesisargumentsobjectvalue" id="utiltypesisargumentsobjectvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isargumentsobject_value"></a></h4>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is an <code>arguments</code> object.</p>
<!-- eslint-disable prefer-rest-params -->
<pre><code class="language-js"><span class="hljs-keyword">function</span> <span class="hljs-title function_">foo</span>(<span class="hljs-params"></span>) {
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isArgumentsObject</span>(<span class="hljs-variable language_">arguments</span>); <span class="hljs-comment">// Returns true</span>
}</code> <button class="copy-button">copy</button></pre>
<h4><code>util.types.isArrayBuffer(value)</code><span><a class="mark" href="#utiltypesisarraybuffervalue" id="utiltypesisarraybuffervalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isarraybuffer_value"></a></h4>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer"><code>ArrayBuffer</code></a> instance.
This does <em>not</em> include <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer"><code>SharedArrayBuffer</code></a> instances. Usually, it is
desirable to test for both; See <a href="#utiltypesisanyarraybuffervalue"><code>util.types.isAnyArrayBuffer()</code></a> for that.</p>
<pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isArrayBuffer</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">ArrayBuffer</span>()); <span class="hljs-comment">// Returns true</span>
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isArrayBuffer</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">SharedArrayBuffer</span>()); <span class="hljs-comment">// Returns false</span></code> <button class="copy-button">copy</button></pre>
<h4><code>util.types.isAsyncFunction(value)</code><span><a class="mark" href="#utiltypesisasyncfunctionvalue" id="utiltypesisasyncfunctionvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isasyncfunction_value"></a></h4>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is an <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/async_function">async function</a>.
This only reports back what the JavaScript engine is seeing;
in particular, the return value may not match the original source code if
a transpilation tool was used.</p>
<pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isAsyncFunction</span>(<span class="hljs-keyword">function</span> <span class="hljs-title function_">foo</span>(<span class="hljs-params"></span>) {}); <span class="hljs-comment">// Returns false</span>
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isAsyncFunction</span>(<span class="hljs-keyword">async</span> <span class="hljs-keyword">function</span> <span class="hljs-title function_">foo</span>(<span class="hljs-params"></span>) {}); <span class="hljs-comment">// Returns true</span></code> <button class="copy-button">copy</button></pre>
<h4><code>util.types.isBigInt64Array(value)</code><span><a class="mark" href="#utiltypesisbigint64arrayvalue" id="utiltypesisbigint64arrayvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isbigint64array_value"></a></h4>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a <code>BigInt64Array</code> instance.</p>
<pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isBigInt64Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">BigInt64Array</span>()); <span class="hljs-comment">// Returns true</span>
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isBigInt64Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">BigUint64Array</span>()); <span class="hljs-comment">// Returns false</span></code> <button class="copy-button">copy</button></pre>
<h4><code>util.types.isBigUint64Array(value)</code><span><a class="mark" href="#utiltypesisbiguint64arrayvalue" id="utiltypesisbiguint64arrayvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isbiguint64array_value"></a></h4>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a <code>BigUint64Array</code> instance.</p>
<pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isBigUint64Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">BigInt64Array</span>()); <span class="hljs-comment">// Returns false</span>
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isBigUint64Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">BigUint64Array</span>()); <span class="hljs-comment">// Returns true</span></code> <button class="copy-button">copy</button></pre>
<h4><code>util.types.isBooleanObject(value)</code><span><a class="mark" href="#utiltypesisbooleanobjectvalue" id="utiltypesisbooleanobjectvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isbooleanobject_value"></a></h4>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a boolean object, e.g. created
by <code>new Boolean()</code>.</p>
<pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isBooleanObject</span>(<span class="hljs-literal">false</span>); <span class="hljs-comment">// Returns false</span>
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isBooleanObject</span>(<span class="hljs-literal">true</span>); <span class="hljs-comment">// Returns false</span>
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isBooleanObject</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Boolean</span>(<span class="hljs-literal">false</span>)); <span class="hljs-comment">// Returns true</span>
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isBooleanObject</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Boolean</span>(<span class="hljs-literal">true</span>)); <span class="hljs-comment">// Returns true</span>
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isBooleanObject</span>(<span class="hljs-title class_">Boolean</span>(<span class="hljs-literal">false</span>)); <span class="hljs-comment">// Returns false</span>
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isBooleanObject</span>(<span class="hljs-title class_">Boolean</span>(<span class="hljs-literal">true</span>)); <span class="hljs-comment">// Returns false</span></code> <button class="copy-button">copy</button></pre>
<h4><code>util.types.isBoxedPrimitive(value)</code><span><a class="mark" href="#utiltypesisboxedprimitivevalue" id="utiltypesisboxedprimitivevalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isboxedprimitive_value"></a></h4>
<div class="api_metadata">
<span>Added in: v10.11.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is any boxed primitive object, e.g. created
by <code>new Boolean()</code>, <code>new String()</code> or <code>Object(Symbol())</code>.</p>
<p>For example:</p>
<pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isBoxedPrimitive</span>(<span class="hljs-literal">false</span>); <span class="hljs-comment">// Returns false</span>
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isBoxedPrimitive</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Boolean</span>(<span class="hljs-literal">false</span>)); <span class="hljs-comment">// Returns true</span>
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isBoxedPrimitive</span>(<span class="hljs-title class_">Symbol</span>(<span class="hljs-string">'foo'</span>)); <span class="hljs-comment">// Returns false</span>
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isBoxedPrimitive</span>(<span class="hljs-title class_">Object</span>(<span class="hljs-title class_">Symbol</span>(<span class="hljs-string">'foo'</span>))); <span class="hljs-comment">// Returns true</span>
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isBoxedPrimitive</span>(<span class="hljs-title class_">Object</span>(<span class="hljs-title class_">BigInt</span>(<span class="hljs-number">5</span>))); <span class="hljs-comment">// Returns true</span></code> <button class="copy-button">copy</button></pre>
<h4><code>util.types.isCryptoKey(value)</code><span><a class="mark" href="#utiltypesiscryptokeyvalue" id="utiltypesiscryptokeyvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_iscryptokey_value"></a></h4>
<div class="api_metadata">
<span>Added in: v16.2.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if <code>value</code> is a <a href="webcrypto.html#class-cryptokey" class="type"><CryptoKey></a>, <code>false</code> otherwise.</p>
<h4><code>util.types.isDataView(value)</code><span><a class="mark" href="#utiltypesisdataviewvalue" id="utiltypesisdataviewvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isdataview_value"></a></h4>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView"><code>DataView</code></a> instance.</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> ab = <span class="hljs-keyword">new</span> <span class="hljs-title class_">ArrayBuffer</span>(<span class="hljs-number">20</span>);
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isDataView</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">DataView</span>(ab)); <span class="hljs-comment">// Returns true</span>
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isDataView</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Float64Array</span>()); <span class="hljs-comment">// Returns false</span></code> <button class="copy-button">copy</button></pre>
<p>See also <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer/isView"><code>ArrayBuffer.isView()</code></a>.</p>
<h4><code>util.types.isDate(value)</code><span><a class="mark" href="#utiltypesisdatevalue" id="utiltypesisdatevalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isdate_value"></a></h4>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date"><code>Date</code></a> instance.</p>
<pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isDate</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Date</span>()); <span class="hljs-comment">// Returns true</span></code> <button class="copy-button">copy</button></pre>
<h4><code>util.types.isExternal(value)</code><span><a class="mark" href="#utiltypesisexternalvalue" id="utiltypesisexternalvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isexternal_value"></a></h4>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a native <code>External</code> value.</p>
<p>A native <code>External</code> value is a special type of object that contains a
raw C++ pointer (<code>void*</code>) for access from native code, and has no other
properties. Such objects are created either by Node.js internals or native
addons. In JavaScript, they are <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/freeze">frozen</a> objects with a
<code>null</code> prototype.</p>
<pre><code class="language-c"><span class="hljs-meta">#<span class="hljs-keyword">include</span> <span class="hljs-string"><js_native_api.h></span></span>
<span class="hljs-meta">#<span class="hljs-keyword">include</span> <span class="hljs-string"><stdlib.h></span></span>
napi_value result;
<span class="hljs-type">static</span> napi_value <span class="hljs-title function_">MyNapi</span><span class="hljs-params">(napi_env env, napi_callback_info info)</span> {
<span class="hljs-type">int</span>* raw = (<span class="hljs-type">int</span>*) <span class="hljs-built_in">malloc</span>(<span class="hljs-number">1024</span>);
napi_status status = napi_create_external(env, (<span class="hljs-type">void</span>*) raw, <span class="hljs-literal">NULL</span>, <span class="hljs-literal">NULL</span>, &result);
<span class="hljs-keyword">if</span> (status != napi_ok) {
napi_throw_error(env, <span class="hljs-literal">NULL</span>, <span class="hljs-string">"napi_create_external failed"</span>);
<span class="hljs-keyword">return</span> <span class="hljs-literal">NULL</span>;
}
<span class="hljs-keyword">return</span> result;
}
...
DECLARE_NAPI_PROPERTY(<span class="hljs-string">"myNapi"</span>, MyNapi)
...</code> <button class="copy-button">copy</button></pre>
<pre><code class="language-js"><span class="hljs-keyword">const</span> native = <span class="hljs-built_in">require</span>(<span class="hljs-string">'napi_addon.node'</span>);
<span class="hljs-keyword">const</span> data = native.<span class="hljs-title function_">myNapi</span>();
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isExternal</span>(data); <span class="hljs-comment">// returns true</span>
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isExternal</span>(<span class="hljs-number">0</span>); <span class="hljs-comment">// returns false</span>
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isExternal</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">String</span>(<span class="hljs-string">'foo'</span>)); <span class="hljs-comment">// returns false</span></code> <button class="copy-button">copy</button></pre>
<p>For further information on <code>napi_create_external</code>, refer to
<a href="n-api.html#napi_create_external"><code>napi_create_external()</code></a>.</p>
<h4><code>util.types.isFloat32Array(value)</code><span><a class="mark" href="#utiltypesisfloat32arrayvalue" id="utiltypesisfloat32arrayvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isfloat32array_value"></a></h4>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Float32Array"><code>Float32Array</code></a> instance.</p>
<pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isFloat32Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">ArrayBuffer</span>()); <span class="hljs-comment">// Returns false</span>
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isFloat32Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Float32Array</span>()); <span class="hljs-comment">// Returns true</span>
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isFloat32Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Float64Array</span>()); <span class="hljs-comment">// Returns false</span></code> <button class="copy-button">copy</button></pre>
<h4><code>util.types.isFloat64Array(value)</code><span><a class="mark" href="#utiltypesisfloat64arrayvalue" id="utiltypesisfloat64arrayvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isfloat64array_value"></a></h4>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Float64Array"><code>Float64Array</code></a> instance.</p>
<pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isFloat64Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">ArrayBuffer</span>()); <span class="hljs-comment">// Returns false</span>
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isFloat64Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Uint8Array</span>()); <span class="hljs-comment">// Returns false</span>
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isFloat64Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Float64Array</span>()); <span class="hljs-comment">// Returns true</span></code> <button class="copy-button">copy</button></pre>
<h4><code>util.types.isGeneratorFunction(value)</code><span><a class="mark" href="#utiltypesisgeneratorfunctionvalue" id="utiltypesisgeneratorfunctionvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isgeneratorfunction_value"></a></h4>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a generator function.
This only reports back what the JavaScript engine is seeing;
in particular, the return value may not match the original source code if
a transpilation tool was used.</p>
<pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isGeneratorFunction</span>(<span class="hljs-keyword">function</span> <span class="hljs-title function_">foo</span>(<span class="hljs-params"></span>) {}); <span class="hljs-comment">// Returns false</span>
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isGeneratorFunction</span>(<span class="hljs-keyword">function</span>* <span class="hljs-title function_">foo</span>(<span class="hljs-params"></span>) {}); <span class="hljs-comment">// Returns true</span></code> <button class="copy-button">copy</button></pre>
<h4><code>util.types.isGeneratorObject(value)</code><span><a class="mark" href="#utiltypesisgeneratorobjectvalue" id="utiltypesisgeneratorobjectvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isgeneratorobject_value"></a></h4>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a generator object as returned from a
built-in generator function.
This only reports back what the JavaScript engine is seeing;
in particular, the return value may not match the original source code if
a transpilation tool was used.</p>
<pre><code class="language-js"><span class="hljs-keyword">function</span>* <span class="hljs-title function_">foo</span>(<span class="hljs-params"></span>) {}
<span class="hljs-keyword">const</span> generator = <span class="hljs-title function_">foo</span>();
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isGeneratorObject</span>(generator); <span class="hljs-comment">// Returns true</span></code> <button class="copy-button">copy</button></pre>
<h4><code>util.types.isInt8Array(value)</code><span><a class="mark" href="#utiltypesisint8arrayvalue" id="utiltypesisint8arrayvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isint8array_value"></a></h4>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Int8Array"><code>Int8Array</code></a> instance.</p>
<pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isInt8Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">ArrayBuffer</span>()); <span class="hljs-comment">// Returns false</span>
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isInt8Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Int8Array</span>()); <span class="hljs-comment">// Returns true</span>
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isInt8Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Float64Array</span>()); <span class="hljs-comment">// Returns false</span></code> <button class="copy-button">copy</button></pre>
<h4><code>util.types.isInt16Array(value)</code><span><a class="mark" href="#utiltypesisint16arrayvalue" id="utiltypesisint16arrayvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isint16array_value"></a></h4>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Int16Array"><code>Int16Array</code></a> instance.</p>
<pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isInt16Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">ArrayBuffer</span>()); <span class="hljs-comment">// Returns false</span>
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isInt16Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Int16Array</span>()); <span class="hljs-comment">// Returns true</span>
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isInt16Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Float64Array</span>()); <span class="hljs-comment">// Returns false</span></code> <button class="copy-button">copy</button></pre>
<h4><code>util.types.isInt32Array(value)</code><span><a class="mark" href="#utiltypesisint32arrayvalue" id="utiltypesisint32arrayvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isint32array_value"></a></h4>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Int32Array"><code>Int32Array</code></a> instance.</p>
<pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isInt32Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">ArrayBuffer</span>()); <span class="hljs-comment">// Returns false</span>
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isInt32Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Int32Array</span>()); <span class="hljs-comment">// Returns true</span>
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isInt32Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Float64Array</span>()); <span class="hljs-comment">// Returns false</span></code> <button class="copy-button">copy</button></pre>
<h4><code>util.types.isKeyObject(value)</code><span><a class="mark" href="#utiltypesiskeyobjectvalue" id="utiltypesiskeyobjectvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_iskeyobject_value"></a></h4>
<div class="api_metadata">
<span>Added in: v16.2.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if <code>value</code> is a <a href="crypto.html#class-keyobject" class="type"><KeyObject></a>, <code>false</code> otherwise.</p>
<h4><code>util.types.isMap(value)</code><span><a class="mark" href="#utiltypesismapvalue" id="utiltypesismapvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_ismap_value"></a></h4>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map"><code>Map</code></a> instance.</p>
<pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isMap</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Map</span>()); <span class="hljs-comment">// Returns true</span></code> <button class="copy-button">copy</button></pre>
<h4><code>util.types.isMapIterator(value)</code><span><a class="mark" href="#utiltypesismapiteratorvalue" id="utiltypesismapiteratorvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_ismapiterator_value"></a></h4>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is an iterator returned for a built-in
<a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map"><code>Map</code></a> instance.</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> map = <span class="hljs-keyword">new</span> <span class="hljs-title class_">Map</span>();
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isMapIterator</span>(map.<span class="hljs-title function_">keys</span>()); <span class="hljs-comment">// Returns true</span>
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isMapIterator</span>(map.<span class="hljs-title function_">values</span>()); <span class="hljs-comment">// Returns true</span>
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isMapIterator</span>(map.<span class="hljs-title function_">entries</span>()); <span class="hljs-comment">// Returns true</span>
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isMapIterator</span>(map[<span class="hljs-title class_">Symbol</span>.<span class="hljs-property">iterator</span>]()); <span class="hljs-comment">// Returns true</span></code> <button class="copy-button">copy</button></pre>
<h4><code>util.types.isModuleNamespaceObject(value)</code><span><a class="mark" href="#utiltypesismodulenamespaceobjectvalue" id="utiltypesismodulenamespaceobjectvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_ismodulenamespaceobject_value"></a></h4>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is an instance of a <a href="https://tc39.github.io/ecma262/#sec-module-namespace-exotic-objects">Module Namespace Object</a>.</p>
<pre><code class="language-js mjs"><span class="hljs-keyword">import</span> * <span class="hljs-keyword">as</span> ns <span class="hljs-keyword">from</span> <span class="hljs-string">'./a.js'</span>;
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isModuleNamespaceObject</span>(ns); <span class="hljs-comment">// Returns true</span></code> <button class="copy-button">copy</button></pre>
<h4><code>util.types.isNativeError(value)</code><span><a class="mark" href="#utiltypesisnativeerrorvalue" id="utiltypesisnativeerrorvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isnativeerror_value"></a></h4>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value was returned by the constructor of a
<a href="https://tc39.es/ecma262/#sec-error-objects">built-in <code>Error</code> type</a>.</p>
<pre><code class="language-js"><span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isNativeError</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Error</span>())); <span class="hljs-comment">// true</span>
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isNativeError</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">TypeError</span>())); <span class="hljs-comment">// true</span>
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isNativeError</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">RangeError</span>())); <span class="hljs-comment">// true</span></code> <button class="copy-button">copy</button></pre>
<p>Subclasses of the native error types are also native errors:</p>
<pre><code class="language-js"><span class="hljs-keyword">class</span> <span class="hljs-title class_">MyError</span> <span class="hljs-keyword">extends</span> <span class="hljs-title class_ inherited__">Error</span> {}
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isNativeError</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">MyError</span>())); <span class="hljs-comment">// true</span></code> <button class="copy-button">copy</button></pre>
<p>A value being <code>instanceof</code> a native error class is not equivalent to <code>isNativeError()</code>
returning <code>true</code> for that value. <code>isNativeError()</code> returns <code>true</code> for errors
which come from a different <a href="https://tc39.es/ecma262/#realm">realm</a> while <code>instanceof Error</code> returns <code>false</code>
for these errors:</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> vm = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:vm'</span>);
<span class="hljs-keyword">const</span> context = vm.<span class="hljs-title function_">createContext</span>({});
<span class="hljs-keyword">const</span> myError = vm.<span class="hljs-title function_">runInContext</span>(<span class="hljs-string">'new Error()'</span>, context);
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isNativeError</span>(myError)); <span class="hljs-comment">// true</span>
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(myError <span class="hljs-keyword">instanceof</span> <span class="hljs-title class_">Error</span>); <span class="hljs-comment">// false</span></code> <button class="copy-button">copy</button></pre>
<p>Conversely, <code>isNativeError()</code> returns <code>false</code> for all objects which were not
returned by the constructor of a native error. That includes values
which are <code>instanceof</code> native errors:</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> myError = { <span class="hljs-attr">__proto__</span>: <span class="hljs-title class_">Error</span>.<span class="hljs-property"><span class="hljs-keyword">prototype</span></span> };
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isNativeError</span>(myError)); <span class="hljs-comment">// false</span>
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(myError <span class="hljs-keyword">instanceof</span> <span class="hljs-title class_">Error</span>); <span class="hljs-comment">// true</span></code> <button class="copy-button">copy</button></pre>
<h4><code>util.types.isNumberObject(value)</code><span><a class="mark" href="#utiltypesisnumberobjectvalue" id="utiltypesisnumberobjectvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isnumberobject_value"></a></h4>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a number object, e.g. created
by <code>new Number()</code>.</p>
<pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isNumberObject</span>(<span class="hljs-number">0</span>); <span class="hljs-comment">// Returns false</span>
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isNumberObject</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Number</span>(<span class="hljs-number">0</span>)); <span class="hljs-comment">// Returns true</span></code> <button class="copy-button">copy</button></pre>
<h4><code>util.types.isPromise(value)</code><span><a class="mark" href="#utiltypesispromisevalue" id="utiltypesispromisevalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_ispromise_value"></a></h4>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise"><code>Promise</code></a>.</p>
<pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isPromise</span>(<span class="hljs-title class_">Promise</span>.<span class="hljs-title function_">resolve</span>(<span class="hljs-number">42</span>)); <span class="hljs-comment">// Returns true</span></code> <button class="copy-button">copy</button></pre>
<h4><code>util.types.isProxy(value)</code><span><a class="mark" href="#utiltypesisproxyvalue" id="utiltypesisproxyvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isproxy_value"></a></h4>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Proxy"><code>Proxy</code></a> instance.</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> target = {};
<span class="hljs-keyword">const</span> proxy = <span class="hljs-keyword">new</span> <span class="hljs-title class_">Proxy</span>(target, {});
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isProxy</span>(target); <span class="hljs-comment">// Returns false</span>
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isProxy</span>(proxy); <span class="hljs-comment">// Returns true</span></code> <button class="copy-button">copy</button></pre>
<h4><code>util.types.isRegExp(value)</code><span><a class="mark" href="#utiltypesisregexpvalue" id="utiltypesisregexpvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isregexp_value"></a></h4>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a regular expression object.</p>
<pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isRegExp</span>(<span class="hljs-regexp">/abc/</span>); <span class="hljs-comment">// Returns true</span>
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isRegExp</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">RegExp</span>(<span class="hljs-string">'abc'</span>)); <span class="hljs-comment">// Returns true</span></code> <button class="copy-button">copy</button></pre>
<h4><code>util.types.isSet(value)</code><span><a class="mark" href="#utiltypesissetvalue" id="utiltypesissetvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isset_value"></a></h4>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set"><code>Set</code></a> instance.</p>
<pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isSet</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Set</span>()); <span class="hljs-comment">// Returns true</span></code> <button class="copy-button">copy</button></pre>
<h4><code>util.types.isSetIterator(value)</code><span><a class="mark" href="#utiltypesissetiteratorvalue" id="utiltypesissetiteratorvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_issetiterator_value"></a></h4>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is an iterator returned for a built-in
<a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set"><code>Set</code></a> instance.</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> set = <span class="hljs-keyword">new</span> <span class="hljs-title class_">Set</span>();
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isSetIterator</span>(set.<span class="hljs-title function_">keys</span>()); <span class="hljs-comment">// Returns true</span>
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isSetIterator</span>(set.<span class="hljs-title function_">values</span>()); <span class="hljs-comment">// Returns true</span>
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isSetIterator</span>(set.<span class="hljs-title function_">entries</span>()); <span class="hljs-comment">// Returns true</span>
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isSetIterator</span>(set[<span class="hljs-title class_">Symbol</span>.<span class="hljs-property">iterator</span>]()); <span class="hljs-comment">// Returns true</span></code> <button class="copy-button">copy</button></pre>
<h4><code>util.types.isSharedArrayBuffer(value)</code><span><a class="mark" href="#utiltypesissharedarraybuffervalue" id="utiltypesissharedarraybuffervalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_issharedarraybuffer_value"></a></h4>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer"><code>SharedArrayBuffer</code></a> instance.
This does <em>not</em> include <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer"><code>ArrayBuffer</code></a> instances. Usually, it is
desirable to test for both; See <a href="#utiltypesisanyarraybuffervalue"><code>util.types.isAnyArrayBuffer()</code></a> for that.</p>
<pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isSharedArrayBuffer</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">ArrayBuffer</span>()); <span class="hljs-comment">// Returns false</span>
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isSharedArrayBuffer</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">SharedArrayBuffer</span>()); <span class="hljs-comment">// Returns true</span></code> <button class="copy-button">copy</button></pre>
<h4><code>util.types.isStringObject(value)</code><span><a class="mark" href="#utiltypesisstringobjectvalue" id="utiltypesisstringobjectvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isstringobject_value"></a></h4>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a string object, e.g. created
by <code>new String()</code>.</p>
<pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isStringObject</span>(<span class="hljs-string">'foo'</span>); <span class="hljs-comment">// Returns false</span>
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isStringObject</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">String</span>(<span class="hljs-string">'foo'</span>)); <span class="hljs-comment">// Returns true</span></code> <button class="copy-button">copy</button></pre>
<h4><code>util.types.isSymbolObject(value)</code><span><a class="mark" href="#utiltypesissymbolobjectvalue" id="utiltypesissymbolobjectvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_issymbolobject_value"></a></h4>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a symbol object, created
by calling <code>Object()</code> on a <code>Symbol</code> primitive.</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> symbol = <span class="hljs-title class_">Symbol</span>(<span class="hljs-string">'foo'</span>);
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isSymbolObject</span>(symbol); <span class="hljs-comment">// Returns false</span>
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isSymbolObject</span>(<span class="hljs-title class_">Object</span>(symbol)); <span class="hljs-comment">// Returns true</span></code> <button class="copy-button">copy</button></pre>
<h4><code>util.types.isTypedArray(value)</code><span><a class="mark" href="#utiltypesistypedarrayvalue" id="utiltypesistypedarrayvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_istypedarray_value"></a></h4>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray"><code>TypedArray</code></a> instance.</p>
<pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isTypedArray</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">ArrayBuffer</span>()); <span class="hljs-comment">// Returns false</span>
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isTypedArray</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Uint8Array</span>()); <span class="hljs-comment">// Returns true</span>
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isTypedArray</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Float64Array</span>()); <span class="hljs-comment">// Returns true</span></code> <button class="copy-button">copy</button></pre>
<p>See also <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer/isView"><code>ArrayBuffer.isView()</code></a>.</p>
<h4><code>util.types.isUint8Array(value)</code><span><a class="mark" href="#utiltypesisuint8arrayvalue" id="utiltypesisuint8arrayvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isuint8array_value"></a></h4>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array"><code>Uint8Array</code></a> instance.</p>
<pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isUint8Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">ArrayBuffer</span>()); <span class="hljs-comment">// Returns false</span>
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isUint8Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Uint8Array</span>()); <span class="hljs-comment">// Returns true</span>
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isUint8Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Float64Array</span>()); <span class="hljs-comment">// Returns false</span></code> <button class="copy-button">copy</button></pre>
<h4><code>util.types.isUint8ClampedArray(value)</code><span><a class="mark" href="#utiltypesisuint8clampedarrayvalue" id="utiltypesisuint8clampedarrayvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isuint8clampedarray_value"></a></h4>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8ClampedArray"><code>Uint8ClampedArray</code></a> instance.</p>
<pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isUint8ClampedArray</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">ArrayBuffer</span>()); <span class="hljs-comment">// Returns false</span>
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isUint8ClampedArray</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Uint8ClampedArray</span>()); <span class="hljs-comment">// Returns true</span>
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isUint8ClampedArray</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Float64Array</span>()); <span class="hljs-comment">// Returns false</span></code> <button class="copy-button">copy</button></pre>
<h4><code>util.types.isUint16Array(value)</code><span><a class="mark" href="#utiltypesisuint16arrayvalue" id="utiltypesisuint16arrayvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isuint16array_value"></a></h4>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint16Array"><code>Uint16Array</code></a> instance.</p>
<pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isUint16Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">ArrayBuffer</span>()); <span class="hljs-comment">// Returns false</span>
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isUint16Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Uint16Array</span>()); <span class="hljs-comment">// Returns true</span>
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isUint16Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Float64Array</span>()); <span class="hljs-comment">// Returns false</span></code> <button class="copy-button">copy</button></pre>
<h4><code>util.types.isUint32Array(value)</code><span><a class="mark" href="#utiltypesisuint32arrayvalue" id="utiltypesisuint32arrayvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isuint32array_value"></a></h4>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint32Array"><code>Uint32Array</code></a> instance.</p>
<pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isUint32Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">ArrayBuffer</span>()); <span class="hljs-comment">// Returns false</span>
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isUint32Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Uint32Array</span>()); <span class="hljs-comment">// Returns true</span>
util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isUint32Array</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Float64Array</span>()); <span class="hljs-comment">// Returns false</span></code> <button class="copy-button">copy</button></pre>
<h4><code>util.types.isWeakMap(value)</code><span><a class="mark" href="#utiltypesisweakmapvalue" id="utiltypesisweakmapvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isweakmap_value"></a></h4>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakMap"><code>WeakMap</code></a> instance.</p>
<pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isWeakMap</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">WeakMap</span>()); <span class="hljs-comment">// Returns true</span></code> <button class="copy-button">copy</button></pre>
<h4><code>util.types.isWeakSet(value)</code><span><a class="mark" href="#utiltypesisweaksetvalue" id="utiltypesisweaksetvalue">#</a></span><a aria-hidden="true" class="legacy" id="util_util_types_isweakset_value"></a></h4>
<div class="api_metadata">
<span>Added in: v10.0.0</span>
</div>
<ul>
<li><code>value</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the value is a built-in <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakSet"><code>WeakSet</code></a> instance.</p>
<pre><code class="language-js">util.<span class="hljs-property">types</span>.<span class="hljs-title function_">isWeakSet</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">WeakSet</span>()); <span class="hljs-comment">// Returns true</span></code> <button class="copy-button">copy</button></pre>
</section><section><h3>Deprecated APIs<span><a class="mark" href="#deprecated-apis" id="deprecated-apis">#</a></span><a aria-hidden="true" class="legacy" id="util_deprecated_apis"></a></h3>
<p>The following APIs are deprecated and should no longer be used. Existing
applications and modules should be updated to find alternative approaches.</p>
<h4><code>util._extend(target, source)</code><span><a class="mark" href="#util_extendtarget-source" id="util_extendtarget-source">#</a></span><a aria-hidden="true" class="legacy" id="util_util_extend_target_source"></a></h4>
<div class="api_metadata">
<span>Added in: v0.7.5</span><span>Deprecated since: v6.0.0</span>
</div>
<p></p><div class="api_stability api_stability_0"><a href="documentation.html#stability-index">Stability: 0</a> - Deprecated: Use <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/assign"><code>Object.assign()</code></a> instead.</div><p></p>
<ul>
<li><code>target</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li>
<li><code>source</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li>
</ul>
<p>The <code>util._extend()</code> method was never intended to be used outside of internal
Node.js modules. The community found and used it anyway.</p>
<p>It is deprecated and should not be used in new code. JavaScript comes with very
similar built-in functionality through <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/assign"><code>Object.assign()</code></a>.</p>
<h4><code>util.isArray(object)</code><span><a class="mark" href="#utilisarrayobject" id="utilisarrayobject">#</a></span><a aria-hidden="true" class="legacy" id="util_util_isarray_object"></a></h4>
<div class="api_metadata">
<span>Added in: v0.6.0</span><span>Deprecated since: v4.0.0</span>
</div>
<p></p><div class="api_stability api_stability_0"><a href="documentation.html#stability-index">Stability: 0</a> - Deprecated: Use <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/isArray"><code>Array.isArray()</code></a> instead.</div><p></p>
<ul>
<li><code>object</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Alias for <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/isArray"><code>Array.isArray()</code></a>.</p>
<p>Returns <code>true</code> if the given <code>object</code> is an <code>Array</code>. Otherwise, returns <code>false</code>.</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);
util.<span class="hljs-title function_">isArray</span>([]);
<span class="hljs-comment">// Returns: true</span>
util.<span class="hljs-title function_">isArray</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Array</span>());
<span class="hljs-comment">// Returns: true</span>
util.<span class="hljs-title function_">isArray</span>({});
<span class="hljs-comment">// Returns: false</span></code> <button class="copy-button">copy</button></pre>
<h4><code>util.isBoolean(object)</code><span><a class="mark" href="#utilisbooleanobject" id="utilisbooleanobject">#</a></span><a aria-hidden="true" class="legacy" id="util_util_isboolean_object"></a></h4>
<div class="api_metadata">
<span>Added in: v0.11.5</span><span>Deprecated since: v4.0.0</span>
</div>
<p></p><div class="api_stability api_stability_0"><a href="documentation.html#stability-index">Stability: 0</a> - Deprecated: Use <code>typeof value === 'boolean'</code> instead.</div><p></p>
<ul>
<li><code>object</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the given <code>object</code> is a <code>Boolean</code>. Otherwise, returns <code>false</code>.</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);
util.<span class="hljs-title function_">isBoolean</span>(<span class="hljs-number">1</span>);
<span class="hljs-comment">// Returns: false</span>
util.<span class="hljs-title function_">isBoolean</span>(<span class="hljs-number">0</span>);
<span class="hljs-comment">// Returns: false</span>
util.<span class="hljs-title function_">isBoolean</span>(<span class="hljs-literal">false</span>);
<span class="hljs-comment">// Returns: true</span></code> <button class="copy-button">copy</button></pre>
<h4><code>util.isBuffer(object)</code><span><a class="mark" href="#utilisbufferobject" id="utilisbufferobject">#</a></span><a aria-hidden="true" class="legacy" id="util_util_isbuffer_object"></a></h4>
<div class="api_metadata">
<span>Added in: v0.11.5</span><span>Deprecated since: v4.0.0</span>
</div>
<p></p><div class="api_stability api_stability_0"><a href="documentation.html#stability-index">Stability: 0</a> - Deprecated: Use <a href="buffer.html#static-method-bufferisbufferobj"><code>Buffer.isBuffer()</code></a> instead.</div><p></p>
<ul>
<li><code>object</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the given <code>object</code> is a <code>Buffer</code>. Otherwise, returns <code>false</code>.</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);
util.<span class="hljs-title function_">isBuffer</span>({ <span class="hljs-attr">length</span>: <span class="hljs-number">0</span> });
<span class="hljs-comment">// Returns: false</span>
util.<span class="hljs-title function_">isBuffer</span>([]);
<span class="hljs-comment">// Returns: false</span>
util.<span class="hljs-title function_">isBuffer</span>(<span class="hljs-title class_">Buffer</span>.<span class="hljs-title function_">from</span>(<span class="hljs-string">'hello world'</span>));
<span class="hljs-comment">// Returns: true</span></code> <button class="copy-button">copy</button></pre>
<h4><code>util.isDate(object)</code><span><a class="mark" href="#utilisdateobject" id="utilisdateobject">#</a></span><a aria-hidden="true" class="legacy" id="util_util_isdate_object"></a></h4>
<div class="api_metadata">
<span>Added in: v0.6.0</span><span>Deprecated since: v4.0.0</span>
</div>
<p></p><div class="api_stability api_stability_0"><a href="documentation.html#stability-index">Stability: 0</a> - Deprecated: Use <a href="#utiltypesisdatevalue"><code>util.types.isDate()</code></a> instead.</div><p></p>
<ul>
<li><code>object</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the given <code>object</code> is a <code>Date</code>. Otherwise, returns <code>false</code>.</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);
util.<span class="hljs-title function_">isDate</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Date</span>());
<span class="hljs-comment">// Returns: true</span>
util.<span class="hljs-title function_">isDate</span>(<span class="hljs-title class_">Date</span>());
<span class="hljs-comment">// false (without 'new' returns a String)</span>
util.<span class="hljs-title function_">isDate</span>({});
<span class="hljs-comment">// Returns: false</span></code> <button class="copy-button">copy</button></pre>
<h4><code>util.isError(object)</code><span><a class="mark" href="#utiliserrorobject" id="utiliserrorobject">#</a></span><a aria-hidden="true" class="legacy" id="util_util_iserror_object"></a></h4>
<div class="api_metadata">
<span>Added in: v0.6.0</span><span>Deprecated since: v4.0.0</span>
</div>
<p></p><div class="api_stability api_stability_0"><a href="documentation.html#stability-index">Stability: 0</a> - Deprecated: Use <a href="#utiltypesisnativeerrorvalue"><code>util.types.isNativeError()</code></a> instead.</div><p></p>
<ul>
<li><code>object</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the given <code>object</code> is an <a href="errors.html#class-error"><code>Error</code></a>. Otherwise, returns
<code>false</code>.</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);
util.<span class="hljs-title function_">isError</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Error</span>());
<span class="hljs-comment">// Returns: true</span>
util.<span class="hljs-title function_">isError</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">TypeError</span>());
<span class="hljs-comment">// Returns: true</span>
util.<span class="hljs-title function_">isError</span>({ <span class="hljs-attr">name</span>: <span class="hljs-string">'Error'</span>, <span class="hljs-attr">message</span>: <span class="hljs-string">'an error occurred'</span> });
<span class="hljs-comment">// Returns: false</span></code> <button class="copy-button">copy</button></pre>
<p>This method relies on <code>Object.prototype.toString()</code> behavior. It is
possible to obtain an incorrect result when the <code>object</code> argument manipulates
<code>@@toStringTag</code>.</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);
<span class="hljs-keyword">const</span> obj = { <span class="hljs-attr">name</span>: <span class="hljs-string">'Error'</span>, <span class="hljs-attr">message</span>: <span class="hljs-string">'an error occurred'</span> };
util.<span class="hljs-title function_">isError</span>(obj);
<span class="hljs-comment">// Returns: false</span>
obj[<span class="hljs-title class_">Symbol</span>.<span class="hljs-property">toStringTag</span>] = <span class="hljs-string">'Error'</span>;
util.<span class="hljs-title function_">isError</span>(obj);
<span class="hljs-comment">// Returns: true</span></code> <button class="copy-button">copy</button></pre>
<h4><code>util.isFunction(object)</code><span><a class="mark" href="#utilisfunctionobject" id="utilisfunctionobject">#</a></span><a aria-hidden="true" class="legacy" id="util_util_isfunction_object"></a></h4>
<div class="api_metadata">
<span>Added in: v0.11.5</span><span>Deprecated since: v4.0.0</span>
</div>
<p></p><div class="api_stability api_stability_0"><a href="documentation.html#stability-index">Stability: 0</a> - Deprecated: Use <code>typeof value === 'function'</code> instead.</div><p></p>
<ul>
<li><code>object</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the given <code>object</code> is a <code>Function</code>. Otherwise, returns
<code>false</code>.</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);
<span class="hljs-keyword">function</span> <span class="hljs-title function_">Foo</span>(<span class="hljs-params"></span>) {}
<span class="hljs-keyword">const</span> <span class="hljs-title function_">Bar</span> = (<span class="hljs-params"></span>) => {};
util.<span class="hljs-title function_">isFunction</span>({});
<span class="hljs-comment">// Returns: false</span>
util.<span class="hljs-title function_">isFunction</span>(<span class="hljs-title class_">Foo</span>);
<span class="hljs-comment">// Returns: true</span>
util.<span class="hljs-title function_">isFunction</span>(<span class="hljs-title class_">Bar</span>);
<span class="hljs-comment">// Returns: true</span></code> <button class="copy-button">copy</button></pre>
<h4><code>util.isNull(object)</code><span><a class="mark" href="#utilisnullobject" id="utilisnullobject">#</a></span><a aria-hidden="true" class="legacy" id="util_util_isnull_object"></a></h4>
<div class="api_metadata">
<span>Added in: v0.11.5</span><span>Deprecated since: v4.0.0</span>
</div>
<p></p><div class="api_stability api_stability_0"><a href="documentation.html#stability-index">Stability: 0</a> - Deprecated: Use <code>value === null</code> instead.</div><p></p>
<ul>
<li><code>object</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the given <code>object</code> is strictly <code>null</code>. Otherwise, returns
<code>false</code>.</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);
util.<span class="hljs-title function_">isNull</span>(<span class="hljs-number">0</span>);
<span class="hljs-comment">// Returns: false</span>
util.<span class="hljs-title function_">isNull</span>(<span class="hljs-literal">undefined</span>);
<span class="hljs-comment">// Returns: false</span>
util.<span class="hljs-title function_">isNull</span>(<span class="hljs-literal">null</span>);
<span class="hljs-comment">// Returns: true</span></code> <button class="copy-button">copy</button></pre>
<h4><code>util.isNullOrUndefined(object)</code><span><a class="mark" href="#utilisnullorundefinedobject" id="utilisnullorundefinedobject">#</a></span><a aria-hidden="true" class="legacy" id="util_util_isnullorundefined_object"></a></h4>
<div class="api_metadata">
<span>Added in: v0.11.5</span><span>Deprecated since: v4.0.0</span>
</div>
<p></p><div class="api_stability api_stability_0"><a href="documentation.html#stability-index">Stability: 0</a> - Deprecated: Use
<code>value === undefined || value === null</code> instead.</div><p></p>
<ul>
<li><code>object</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the given <code>object</code> is <code>null</code> or <code>undefined</code>. Otherwise,
returns <code>false</code>.</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);
util.<span class="hljs-title function_">isNullOrUndefined</span>(<span class="hljs-number">0</span>);
<span class="hljs-comment">// Returns: false</span>
util.<span class="hljs-title function_">isNullOrUndefined</span>(<span class="hljs-literal">undefined</span>);
<span class="hljs-comment">// Returns: true</span>
util.<span class="hljs-title function_">isNullOrUndefined</span>(<span class="hljs-literal">null</span>);
<span class="hljs-comment">// Returns: true</span></code> <button class="copy-button">copy</button></pre>
<h4><code>util.isNumber(object)</code><span><a class="mark" href="#utilisnumberobject" id="utilisnumberobject">#</a></span><a aria-hidden="true" class="legacy" id="util_util_isnumber_object"></a></h4>
<div class="api_metadata">
<span>Added in: v0.11.5</span><span>Deprecated since: v4.0.0</span>
</div>
<p></p><div class="api_stability api_stability_0"><a href="documentation.html#stability-index">Stability: 0</a> - Deprecated: Use <code>typeof value === 'number'</code> instead.</div><p></p>
<ul>
<li><code>object</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the given <code>object</code> is a <code>Number</code>. Otherwise, returns <code>false</code>.</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);
util.<span class="hljs-title function_">isNumber</span>(<span class="hljs-literal">false</span>);
<span class="hljs-comment">// Returns: false</span>
util.<span class="hljs-title function_">isNumber</span>(<span class="hljs-title class_">Infinity</span>);
<span class="hljs-comment">// Returns: true</span>
util.<span class="hljs-title function_">isNumber</span>(<span class="hljs-number">0</span>);
<span class="hljs-comment">// Returns: true</span>
util.<span class="hljs-title function_">isNumber</span>(<span class="hljs-title class_">NaN</span>);
<span class="hljs-comment">// Returns: true</span></code> <button class="copy-button">copy</button></pre>
<h4><code>util.isObject(object)</code><span><a class="mark" href="#utilisobjectobject" id="utilisobjectobject">#</a></span><a aria-hidden="true" class="legacy" id="util_util_isobject_object"></a></h4>
<div class="api_metadata">
<span>Added in: v0.11.5</span><span>Deprecated since: v4.0.0</span>
</div>
<p></p><div class="api_stability api_stability_0"><a href="documentation.html#stability-index">Stability: 0</a> - Deprecated:
Use <code>value !== null && typeof value === 'object'</code> instead.</div><p></p>
<ul>
<li><code>object</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the given <code>object</code> is strictly an <code>Object</code> <strong>and</strong> not a
<code>Function</code> (even though functions are objects in JavaScript).
Otherwise, returns <code>false</code>.</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);
util.<span class="hljs-title function_">isObject</span>(<span class="hljs-number">5</span>);
<span class="hljs-comment">// Returns: false</span>
util.<span class="hljs-title function_">isObject</span>(<span class="hljs-literal">null</span>);
<span class="hljs-comment">// Returns: false</span>
util.<span class="hljs-title function_">isObject</span>({});
<span class="hljs-comment">// Returns: true</span>
util.<span class="hljs-title function_">isObject</span>(<span class="hljs-function">() =></span> {});
<span class="hljs-comment">// Returns: false</span></code> <button class="copy-button">copy</button></pre>
<h4><code>util.isPrimitive(object)</code><span><a class="mark" href="#utilisprimitiveobject" id="utilisprimitiveobject">#</a></span><a aria-hidden="true" class="legacy" id="util_util_isprimitive_object"></a></h4>
<div class="api_metadata">
<span>Added in: v0.11.5</span><span>Deprecated since: v4.0.0</span>
</div>
<p></p><div class="api_stability api_stability_0"><a href="documentation.html#stability-index">Stability: 0</a> - Deprecated: Use
<code>(typeof value !== 'object' && typeof value !== 'function') || value === null</code>
instead.</div><p></p>
<ul>
<li><code>object</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the given <code>object</code> is a primitive type. Otherwise, returns
<code>false</code>.</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);
util.<span class="hljs-title function_">isPrimitive</span>(<span class="hljs-number">5</span>);
<span class="hljs-comment">// Returns: true</span>
util.<span class="hljs-title function_">isPrimitive</span>(<span class="hljs-string">'foo'</span>);
<span class="hljs-comment">// Returns: true</span>
util.<span class="hljs-title function_">isPrimitive</span>(<span class="hljs-literal">false</span>);
<span class="hljs-comment">// Returns: true</span>
util.<span class="hljs-title function_">isPrimitive</span>(<span class="hljs-literal">null</span>);
<span class="hljs-comment">// Returns: true</span>
util.<span class="hljs-title function_">isPrimitive</span>(<span class="hljs-literal">undefined</span>);
<span class="hljs-comment">// Returns: true</span>
util.<span class="hljs-title function_">isPrimitive</span>({});
<span class="hljs-comment">// Returns: false</span>
util.<span class="hljs-title function_">isPrimitive</span>(<span class="hljs-function">() =></span> {});
<span class="hljs-comment">// Returns: false</span>
util.<span class="hljs-title function_">isPrimitive</span>(<span class="hljs-regexp">/^$/</span>);
<span class="hljs-comment">// Returns: false</span>
util.<span class="hljs-title function_">isPrimitive</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">Date</span>());
<span class="hljs-comment">// Returns: false</span></code> <button class="copy-button">copy</button></pre>
<h4><code>util.isRegExp(object)</code><span><a class="mark" href="#utilisregexpobject" id="utilisregexpobject">#</a></span><a aria-hidden="true" class="legacy" id="util_util_isregexp_object"></a></h4>
<div class="api_metadata">
<span>Added in: v0.6.0</span><span>Deprecated since: v4.0.0</span>
</div>
<p></p><div class="api_stability api_stability_0"><a href="documentation.html#stability-index">Stability: 0</a> - Deprecated</div><p></p>
<ul>
<li><code>object</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the given <code>object</code> is a <code>RegExp</code>. Otherwise, returns <code>false</code>.</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);
util.<span class="hljs-title function_">isRegExp</span>(<span class="hljs-regexp">/some regexp/</span>);
<span class="hljs-comment">// Returns: true</span>
util.<span class="hljs-title function_">isRegExp</span>(<span class="hljs-keyword">new</span> <span class="hljs-title class_">RegExp</span>(<span class="hljs-string">'another regexp'</span>));
<span class="hljs-comment">// Returns: true</span>
util.<span class="hljs-title function_">isRegExp</span>({});
<span class="hljs-comment">// Returns: false</span></code> <button class="copy-button">copy</button></pre>
<h4><code>util.isString(object)</code><span><a class="mark" href="#utilisstringobject" id="utilisstringobject">#</a></span><a aria-hidden="true" class="legacy" id="util_util_isstring_object"></a></h4>
<div class="api_metadata">
<span>Added in: v0.11.5</span><span>Deprecated since: v4.0.0</span>
</div>
<p></p><div class="api_stability api_stability_0"><a href="documentation.html#stability-index">Stability: 0</a> - Deprecated: Use <code>typeof value === 'string'</code> instead.</div><p></p>
<ul>
<li><code>object</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the given <code>object</code> is a <code>string</code>. Otherwise, returns <code>false</code>.</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);
util.<span class="hljs-title function_">isString</span>(<span class="hljs-string">''</span>);
<span class="hljs-comment">// Returns: true</span>
util.<span class="hljs-title function_">isString</span>(<span class="hljs-string">'foo'</span>);
<span class="hljs-comment">// Returns: true</span>
util.<span class="hljs-title function_">isString</span>(<span class="hljs-title class_">String</span>(<span class="hljs-string">'foo'</span>));
<span class="hljs-comment">// Returns: true</span>
util.<span class="hljs-title function_">isString</span>(<span class="hljs-number">5</span>);
<span class="hljs-comment">// Returns: false</span></code> <button class="copy-button">copy</button></pre>
<h4><code>util.isSymbol(object)</code><span><a class="mark" href="#utilissymbolobject" id="utilissymbolobject">#</a></span><a aria-hidden="true" class="legacy" id="util_util_issymbol_object"></a></h4>
<div class="api_metadata">
<span>Added in: v0.11.5</span><span>Deprecated since: v4.0.0</span>
</div>
<p></p><div class="api_stability api_stability_0"><a href="documentation.html#stability-index">Stability: 0</a> - Deprecated: Use <code>typeof value === 'symbol'</code> instead.</div><p></p>
<ul>
<li><code>object</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the given <code>object</code> is a <code>Symbol</code>. Otherwise, returns <code>false</code>.</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);
util.<span class="hljs-title function_">isSymbol</span>(<span class="hljs-number">5</span>);
<span class="hljs-comment">// Returns: false</span>
util.<span class="hljs-title function_">isSymbol</span>(<span class="hljs-string">'foo'</span>);
<span class="hljs-comment">// Returns: false</span>
util.<span class="hljs-title function_">isSymbol</span>(<span class="hljs-title class_">Symbol</span>(<span class="hljs-string">'foo'</span>));
<span class="hljs-comment">// Returns: true</span></code> <button class="copy-button">copy</button></pre>
<h4><code>util.isUndefined(object)</code><span><a class="mark" href="#utilisundefinedobject" id="utilisundefinedobject">#</a></span><a aria-hidden="true" class="legacy" id="util_util_isundefined_object"></a></h4>
<div class="api_metadata">
<span>Added in: v0.11.5</span><span>Deprecated since: v4.0.0</span>
</div>
<p></p><div class="api_stability api_stability_0"><a href="documentation.html#stability-index">Stability: 0</a> - Deprecated: Use <code>value === undefined</code> instead.</div><p></p>
<ul>
<li><code>object</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a></li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a></li>
</ul>
<p>Returns <code>true</code> if the given <code>object</code> is <code>undefined</code>. Otherwise, returns <code>false</code>.</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);
<span class="hljs-keyword">const</span> foo = <span class="hljs-literal">undefined</span>;
util.<span class="hljs-title function_">isUndefined</span>(<span class="hljs-number">5</span>);
<span class="hljs-comment">// Returns: false</span>
util.<span class="hljs-title function_">isUndefined</span>(foo);
<span class="hljs-comment">// Returns: true</span>
util.<span class="hljs-title function_">isUndefined</span>(<span class="hljs-literal">null</span>);
<span class="hljs-comment">// Returns: false</span></code> <button class="copy-button">copy</button></pre>
<h4><code>util.log(string)</code><span><a class="mark" href="#utillogstring" id="utillogstring">#</a></span><a aria-hidden="true" class="legacy" id="util_util_log_string"></a></h4>
<div class="api_metadata">
<span>Added in: v0.3.0</span><span>Deprecated since: v6.0.0</span>
</div>
<p></p><div class="api_stability api_stability_0"><a href="documentation.html#stability-index">Stability: 0</a> - Deprecated: Use a third party module instead.</div><p></p>
<ul>
<li><code>string</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li>
</ul>
<p>The <code>util.log()</code> method prints the given <code>string</code> to <code>stdout</code> with an included
timestamp.</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> util = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:util'</span>);
util.<span class="hljs-title function_">log</span>(<span class="hljs-string">'Timestamped message.'</span>);</code> <button class="copy-button">copy</button></pre></section>
<!-- API END -->
</div>
</div>
</div>
</body>
</html>