Server IP : 85.214.239.14 / Your IP : 3.145.65.133 Web Server : Apache/2.4.62 (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 : /usr/share/doc/nodejs/api/ |
Upload File : |
# Util <!--introduced_in=v0.10.0--> > Stability: 2 - Stable <!-- source_link=lib/util.js --> The `node:util` 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: ```js const util = require('node:util'); ``` ## `util.callbackify(original)` <!-- YAML added: v8.2.0 --> * `original` {Function} An `async` function * Returns: {Function} a callback style function Takes an `async` function (or a function that returns a `Promise`) and returns a function following the error-first callback style, i.e. taking an `(err, value) => ...` callback as the last argument. In the callback, the first argument will be the rejection reason (or `null` if the `Promise` resolved), and the second argument will be the resolved value. ```js const util = require('node:util'); async function fn() { return 'hello world'; } const callbackFunction = util.callbackify(fn); callbackFunction((err, ret) => { if (err) throw err; console.log(ret); }); ``` Will print: ```text hello world ``` The callback is executed asynchronously, and will have a limited stack trace. If the callback throws, the process will emit an [`'uncaughtException'`][] event, and if not handled will exit. Since `null` has a special meaning as the first argument to a callback, if a wrapped function rejects a `Promise` with a falsy value as a reason, the value is wrapped in an `Error` with the original value stored in a field named `reason`. ```js function fn() { return Promise.reject(null); } const callbackFunction = util.callbackify(fn); callbackFunction((err, ret) => { // When the Promise was rejected with `null` it is wrapped with an Error and // the original value is stored in `reason`. err && Object.hasOwn(err, 'reason') && err.reason === null; // true }); ``` ## `util.debuglog(section[, callback])` <!-- YAML added: v0.11.3 --> * `section` {string} A string identifying the portion of the application for which the `debuglog` function is being created. * `callback` {Function} A callback invoked the first time the logging function is called with a function argument that is a more optimized logging function. * Returns: {Function} The logging function The `util.debuglog()` method is used to create a function that conditionally writes debug messages to `stderr` based on the existence of the `NODE_DEBUG` environment variable. If the `section` name appears within the value of that environment variable, then the returned function operates similar to [`console.error()`][]. If not, then the returned function is a no-op. ```js const util = require('node:util'); const debuglog = util.debuglog('foo'); debuglog('hello from foo [%d]', 123); ``` If this program is run with `NODE_DEBUG=foo` in the environment, then it will output something like: ```console FOO 3245: hello from foo [123] ``` where `3245` is the process id. If it is not run with that environment variable set, then it will not print anything. The `section` supports wildcard also: ```js const util = require('node:util'); const debuglog = util.debuglog('foo-bar'); debuglog('hi there, it\'s foo-bar [%d]', 2333); ``` if it is run with `NODE_DEBUG=foo*` in the environment, then it will output something like: ```console FOO-BAR 3257: hi there, it's foo-bar [2333] ``` Multiple comma-separated `section` names may be specified in the `NODE_DEBUG` environment variable: `NODE_DEBUG=fs,net,tls`. The optional `callback` argument can be used to replace the logging function with a different function that doesn't have any initialization or unnecessary wrapping. ```js const util = require('node:util'); let debuglog = util.debuglog('internals', (debug) => { // Replace with a logging function that optimizes out // testing if the section is enabled debuglog = debug; }); ``` ### `debuglog().enabled` <!-- YAML added: v14.9.0 --> * {boolean} The `util.debuglog().enabled` getter is used to create a test that can be used in conditionals based on the existence of the `NODE_DEBUG` environment variable. If the `section` name appears within the value of that environment variable, then the returned value will be `true`. If not, then the returned value will be `false`. ```js const util = require('node:util'); const enabled = util.debuglog('foo').enabled; if (enabled) { console.log('hello from foo [%d]', 123); } ``` If this program is run with `NODE_DEBUG=foo` in the environment, then it will output something like: ```console hello from foo [123] ``` ## `util.debug(section)` <!-- YAML added: v14.9.0 --> Alias for `util.debuglog`. Usage allows for readability of that doesn't imply logging when only using `util.debuglog().enabled`. ## `util.deprecate(fn, msg[, code])` <!-- YAML added: v0.8.0 changes: - version: v10.0.0 pr-url: https://github.com/nodejs/node/pull/16393 description: Deprecation warnings are only emitted once for each code. --> * `fn` {Function} The function that is being deprecated. * `msg` {string} A warning message to display when the deprecated function is invoked. * `code` {string} A deprecation code. See the [list of deprecated APIs][] for a list of codes. * Returns: {Function} The deprecated function wrapped to emit a warning. The `util.deprecate()` method wraps `fn` (which may be a function or class) in such a way that it is marked as deprecated. ```js const util = require('node:util'); exports.obsoleteFunction = util.deprecate(() => { // Do something here. }, 'obsoleteFunction() is deprecated. Use newShinyFunction() instead.'); ``` When called, `util.deprecate()` will return a function that will emit a `DeprecationWarning` using the [`'warning'`][] event. The warning will be emitted and printed to `stderr` the first time the returned function is called. After the warning is emitted, the wrapped function is called without emitting a warning. If the same optional `code` is supplied in multiple calls to `util.deprecate()`, the warning will be emitted only once for that `code`. ```js const util = require('node:util'); const fn1 = util.deprecate(someFunction, someMessage, 'DEP0001'); const fn2 = util.deprecate(someOtherFunction, someOtherMessage, 'DEP0001'); fn1(); // Emits a deprecation warning with code DEP0001 fn2(); // Does not emit a deprecation warning because it has the same code ``` If either the `--no-deprecation` or `--no-warnings` command-line flags are used, or if the `process.noDeprecation` property is set to `true` _prior_ to the first deprecation warning, the `util.deprecate()` method does nothing. If the `--trace-deprecation` or `--trace-warnings` command-line flags are set, or the `process.traceDeprecation` property is set to `true`, a warning and a stack trace are printed to `stderr` the first time the deprecated function is called. If the `--throw-deprecation` command-line flag is set, or the `process.throwDeprecation` property is set to `true`, then an exception will be thrown when the deprecated function is called. The `--throw-deprecation` command-line flag and `process.throwDeprecation` property take precedence over `--trace-deprecation` and `process.traceDeprecation`. ## `util.format(format[, ...args])` <!-- YAML added: v0.5.3 changes: - version: v12.11.0 pr-url: https://github.com/nodejs/node/pull/29606 description: The `%c` specifier is ignored now. - version: v12.0.0 pr-url: https://github.com/nodejs/node/pull/23162 description: The `format` argument is now only taken as such if it actually contains format specifiers. - version: v12.0.0 pr-url: https://github.com/nodejs/node/pull/23162 description: If the `format` 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. - version: v11.4.0 pr-url: https://github.com/nodejs/node/pull/23708 description: The `%d`, `%f`, and `%i` specifiers now support Symbols properly. - version: v11.4.0 pr-url: https://github.com/nodejs/node/pull/24806 description: The `%o` specifier's `depth` has default depth of 4 again. - version: v11.0.0 pr-url: https://github.com/nodejs/node/pull/17907 description: The `%o` specifier's `depth` option will now fall back to the default depth. - version: v10.12.0 pr-url: https://github.com/nodejs/node/pull/22097 description: The `%d` and `%i` specifiers now support BigInt. - version: v8.4.0 pr-url: https://github.com/nodejs/node/pull/14558 description: The `%o` and `%O` specifiers are supported now. --> * `format` {string} A `printf`-like format string. The `util.format()` method returns a formatted string using the first argument as a `printf`-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: * `%s`: `String` will be used to convert all values except `BigInt`, `Object` and `-0`. `BigInt` values will be represented with an `n` and Objects that have no user defined `toString` function are inspected using `util.inspect()` with options `{ depth: 0, colors: false, compact: 3 }`. * `%d`: `Number` will be used to convert all values except `BigInt` and `Symbol`. * `%i`: `parseInt(value, 10)` is used for all values except `BigInt` and `Symbol`. * `%f`: `parseFloat(value)` is used for all values expect `Symbol`. * `%j`: JSON. Replaced with the string `'[Circular]'` if the argument contains circular references. * `%o`: `Object`. A string representation of an object with generic JavaScript object formatting. Similar to `util.inspect()` with options `{ showHidden: true, showProxy: true }`. This will show the full object including non-enumerable properties and proxies. * `%O`: `Object`. A string representation of an object with generic JavaScript object formatting. Similar to `util.inspect()` without options. This will show the full object not including non-enumerable properties and proxies. * `%c`: `CSS`. This specifier is ignored and will skip any CSS passed in. * `%%`: single percent sign (`'%'`). This does not consume an argument. * Returns: {string} The formatted string If a specifier does not have a corresponding argument, it is not replaced: ```js util.format('%s:%s', 'foo'); // Returns: 'foo:%s' ``` Values that are not part of the format string are formatted using `util.inspect()` if their type is not `string`. If there are more arguments passed to the `util.format()` method than the number of specifiers, the extra arguments are concatenated to the returned string, separated by spaces: ```js util.format('%s:%s', 'foo', 'bar', 'baz'); // Returns: 'foo:bar baz' ``` If the first argument does not contain a valid format specifier, `util.format()` returns a string that is the concatenation of all arguments separated by spaces: ```js util.format(1, 2, 3); // Returns: '1 2 3' ``` If only one argument is passed to `util.format()`, it is returned as it is without any formatting: ```js util.format('%% %s'); // Returns: '%% %s' ``` `util.format()` 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. ## `util.formatWithOptions(inspectOptions, format[, ...args])` <!-- YAML added: v10.0.0 --> * `inspectOptions` {Object} * `format` {string} This function is identical to [`util.format()`][], except in that it takes an `inspectOptions` argument which specifies options that are passed along to [`util.inspect()`][]. ```js util.formatWithOptions({ colors: true }, 'See object %O', { foo: 42 }); // Returns 'See object { foo: 42 }', where `42` is colored as a number // when printed to a terminal. ``` ## `util.getSystemErrorName(err)` <!-- YAML added: v9.7.0 --> * `err` {number} * Returns: {string} 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 [Common System Errors][] for the names of common errors. ```js fs.access('file/that/does/not/exist', (err) => { const name = util.getSystemErrorName(err.errno); console.error(name); // ENOENT }); ``` ## `util.getSystemErrorMap()` <!-- YAML added: - v16.0.0 - v14.17.0 --> * Returns: {Map} 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 [Common System Errors][] for the names of common errors. ```js fs.access('file/that/does/not/exist', (err) => { const errorMap = util.getSystemErrorMap(); const name = errorMap.get(err.errno); console.error(name); // ENOENT }); ``` ## `util.inherits(constructor, superConstructor)` <!-- YAML added: v0.3.0 changes: - version: v5.0.0 pr-url: https://github.com/nodejs/node/pull/3455 description: The `constructor` parameter can refer to an ES6 class now. --> > Stability: 3 - Legacy: Use ES2015 class syntax and `extends` keyword instead. * `constructor` {Function} * `superConstructor` {Function} Usage of `util.inherits()` is discouraged. Please use the ES6 `class` and `extends` keywords to get language level inheritance support. Also note that the two styles are [semantically incompatible][]. Inherit the prototype methods from one [constructor][] into another. The prototype of `constructor` will be set to a new object created from `superConstructor`. This mainly adds some input validation on top of `Object.setPrototypeOf(constructor.prototype, superConstructor.prototype)`. As an additional convenience, `superConstructor` will be accessible through the `constructor.super_` property. ```js const util = require('node:util'); const EventEmitter = require('node:events'); function MyStream() { EventEmitter.call(this); } util.inherits(MyStream, EventEmitter); MyStream.prototype.write = function(data) { this.emit('data', data); }; const stream = new MyStream(); console.log(stream instanceof EventEmitter); // true console.log(MyStream.super_ === EventEmitter); // true stream.on('data', (data) => { console.log(`Received data: "${data}"`); }); stream.write('It works!'); // Received data: "It works!" ``` ES6 example using `class` and `extends`: ```js const EventEmitter = require('node:events'); class MyStream extends EventEmitter { write(data) { this.emit('data', data); } } const stream = new MyStream(); stream.on('data', (data) => { console.log(`Received data: "${data}"`); }); stream.write('With ES6'); ``` ## `util.inspect(object[, options])` ## `util.inspect(object[, showHidden[, depth[, colors]]])` <!-- YAML added: v0.3.0 changes: - version: - v17.3.0 - v16.14.0 pr-url: https://github.com/nodejs/node/pull/41003 description: The `numericSeparator` option is supported now. - version: v16.18.0 pr-url: https://github.com/nodejs/node/pull/43576 description: add support for `maxArrayLength` when inspecting `Set` and `Map`. - version: - v14.6.0 - v12.19.0 pr-url: https://github.com/nodejs/node/pull/33690 description: If `object` is from a different `vm.Context` now, a custom inspection function on it will not receive context-specific arguments anymore. - version: - v13.13.0 - v12.17.0 pr-url: https://github.com/nodejs/node/pull/32392 description: The `maxStringLength` option is supported now. - version: - v13.5.0 - v12.16.0 pr-url: https://github.com/nodejs/node/pull/30768 description: User defined prototype properties are inspected in case `showHidden` is `true`. - version: v13.0.0 pr-url: https://github.com/nodejs/node/pull/27685 description: Circular references now include a marker to the reference. - version: v12.0.0 pr-url: https://github.com/nodejs/node/pull/27109 description: The `compact` options default is changed to `3` and the `breakLength` options default is changed to `80`. - version: v12.0.0 pr-url: https://github.com/nodejs/node/pull/24971 description: Internal properties no longer appear in the context argument of a custom inspection function. - version: v11.11.0 pr-url: https://github.com/nodejs/node/pull/26269 description: The `compact` option accepts numbers for a new output mode. - version: v11.7.0 pr-url: https://github.com/nodejs/node/pull/25006 description: ArrayBuffers now also show their binary contents. - version: v11.5.0 pr-url: https://github.com/nodejs/node/pull/24852 description: The `getters` option is supported now. - version: v11.4.0 pr-url: https://github.com/nodejs/node/pull/24326 description: The `depth` default changed back to `2`. - version: v11.0.0 pr-url: https://github.com/nodejs/node/pull/22846 description: The `depth` default changed to `20`. - version: v11.0.0 pr-url: https://github.com/nodejs/node/pull/22756 description: The inspection output is now limited to about 128 MiB. Data above that size will not be fully inspected. - version: v10.12.0 pr-url: https://github.com/nodejs/node/pull/22788 description: The `sorted` option is supported now. - version: v10.6.0 pr-url: https://github.com/nodejs/node/pull/20725 description: Inspecting linked lists and similar objects is now possible up to the maximum call stack size. - version: v10.0.0 pr-url: https://github.com/nodejs/node/pull/19259 description: The `WeakMap` and `WeakSet` entries can now be inspected as well. - version: v9.9.0 pr-url: https://github.com/nodejs/node/pull/17576 description: The `compact` option is supported now. - version: v6.6.0 pr-url: https://github.com/nodejs/node/pull/8174 description: Custom inspection functions can now return `this`. - version: v6.3.0 pr-url: https://github.com/nodejs/node/pull/7499 description: The `breakLength` option is supported now. - version: v6.1.0 pr-url: https://github.com/nodejs/node/pull/6334 description: The `maxArrayLength` option is supported now; in particular, long arrays are truncated by default. - version: v6.1.0 pr-url: https://github.com/nodejs/node/pull/6465 description: The `showProxy` option is supported now. --> * `object` {any} Any JavaScript primitive or `Object`. * `options` {Object} * `showHidden` {boolean} If `true`, `object`'s non-enumerable symbols and properties are included in the formatted result. [`WeakMap`][] and [`WeakSet`][] entries are also included as well as user defined prototype properties (excluding method properties). **Default:** `false`. * `depth` {number} Specifies the number of times to recurse while formatting `object`. This is useful for inspecting large objects. To recurse up to the maximum call stack size pass `Infinity` or `null`. **Default:** `2`. * `colors` {boolean} If `true`, the output is styled with ANSI color codes. Colors are customizable. See [Customizing `util.inspect` colors][]. **Default:** `false`. * `customInspect` {boolean} If `false`, `[util.inspect.custom](depth, opts, inspect)` functions are not invoked. **Default:** `true`. * `showProxy` {boolean} If `true`, `Proxy` inspection includes the [`target` and `handler`][] objects. **Default:** `false`. * `maxArrayLength` {integer} Specifies the maximum number of `Array`, [`TypedArray`][], [`Map`][], [`Set`][], [`WeakMap`][], and [`WeakSet`][] elements to include when formatting. Set to `null` or `Infinity` to show all elements. Set to `0` or negative to show no elements. **Default:** `100`. * `maxStringLength` {integer} Specifies the maximum number of characters to include when formatting. Set to `null` or `Infinity` to show all elements. Set to `0` or negative to show no characters. **Default:** `10000`. * `breakLength` {integer} The length at which input values are split across multiple lines. Set to `Infinity` to format the input as a single line (in combination with `compact` set to `true` or any number >= `1`). **Default:** `80`. * `compact` {boolean|integer} Setting this to `false` causes each object key to be displayed on a new line. It will break on new lines in text that is longer than `breakLength`. If set to a number, the most `n` inner elements are united on a single line as long as all properties fit into `breakLength`. Short array elements are also grouped together. For more information, see the example below. **Default:** `3`. * `sorted` {boolean|Function} If set to `true` or a function, all properties of an object, and `Set` and `Map` entries are sorted in the resulting string. If set to `true` the [default sort][] is used. If set to a function, it is used as a [compare function][]. * `getters` {boolean|string} If set to `true`, getters are inspected. If set to `'get'`, only getters without a corresponding setter are inspected. If set to `'set'`, only getters with a corresponding setter are inspected. This might cause side effects depending on the getter function. **Default:** `false`. * `numericSeparator` {boolean} If set to `true`, an underscore is used to separate every three digits in all bigints and numbers. **Default:** `false`. * Returns: {string} The representation of `object`. The `util.inspect()` method returns a string representation of `object` that is intended for debugging. The output of `util.inspect` may change at any time and should not be depended upon programmatically. Additional `options` may be passed that alter the result. `util.inspect()` will use the constructor's name and/or `@@toStringTag` to make an identifiable tag for an inspected value. ```js class Foo { get [Symbol.toStringTag]() { return 'bar'; } } class Bar {} const baz = Object.create(null, { [Symbol.toStringTag]: { value: 'foo' } }); util.inspect(new Foo()); // 'Foo [bar] {}' util.inspect(new Bar()); // 'Bar {}' util.inspect(baz); // '[foo] {}' ``` Circular references point to their anchor by using a reference index: ```js const { inspect } = require('node:util'); const obj = {}; obj.a = [obj]; obj.b = {}; obj.b.inner = obj.b; obj.b.obj = obj; console.log(inspect(obj)); // <ref *1> { // a: [ [Circular *1] ], // b: <ref *2> { inner: [Circular *2], obj: [Circular *1] } // } ``` The following example inspects all properties of the `util` object: ```js const util = require('node:util'); console.log(util.inspect(util, { showHidden: true, depth: null })); ``` The following example highlights the effect of the `compact` option: ```js const util = require('node:util'); const o = { a: [1, 2, [[ 'Lorem ipsum dolor sit amet,\nconsectetur adipiscing elit, sed do ' + 'eiusmod \ntempor incididunt ut labore et dolore magna aliqua.', 'test', 'foo']], 4], b: new Map([['za', 1], ['zb', 'test']]), }; console.log(util.inspect(o, { compact: true, depth: 5, breakLength: 80 })); // { a: // [ 1, // 2, // [ [ 'Lorem ipsum dolor sit amet,\nconsectetur [...]', // A long line // 'test', // 'foo' ] ], // 4 ], // b: Map(2) { 'za' => 1, 'zb' => 'test' } } // Setting `compact` to false or an integer creates more reader friendly output. console.log(util.inspect(o, { compact: false, depth: 5, breakLength: 80 })); // { // a: [ // 1, // 2, // [ // [ // 'Lorem ipsum dolor sit amet,\n' + // 'consectetur adipiscing elit, sed do eiusmod \n' + // 'tempor incididunt ut labore et dolore magna aliqua.', // 'test', // 'foo' // ] // ], // 4 // ], // b: Map(2) { // 'za' => 1, // 'zb' => 'test' // } // } // Setting `breakLength` to e.g. 150 will print the "Lorem ipsum" text in a // single line. ``` The `showHidden` option allows [`WeakMap`][] and [`WeakSet`][] entries to be inspected. If there are more entries than `maxArrayLength`, there is no guarantee which entries are displayed. That means retrieving the same [`WeakSet`][] entries twice may result in different output. Furthermore, entries with no remaining strong references may be garbage collected at any time. ```js const { inspect } = require('node:util'); const obj = { a: 1 }; const obj2 = { b: 2 }; const weakSet = new WeakSet([obj, obj2]); console.log(inspect(weakSet, { showHidden: true })); // WeakSet { { a: 1 }, { b: 2 } } ``` The `sorted` option ensures that an object's property insertion order does not impact the result of `util.inspect()`. ```js const { inspect } = require('node:util'); const assert = require('node:assert'); const o1 = { b: [2, 3, 1], a: '`a` comes before `b`', c: new Set([2, 3, 1]), }; console.log(inspect(o1, { sorted: true })); // { a: '`a` comes before `b`', b: [ 2, 3, 1 ], c: Set(3) { 1, 2, 3 } } console.log(inspect(o1, { sorted: (a, b) => b.localeCompare(a) })); // { c: Set(3) { 3, 2, 1 }, b: [ 2, 3, 1 ], a: '`a` comes before `b`' } const o2 = { c: new Set([2, 1, 3]), a: '`a` comes before `b`', b: [2, 3, 1], }; assert.strict.equal( inspect(o1, { sorted: true }), inspect(o2, { sorted: true }), ); ``` The `numericSeparator` option adds an underscore every three digits to all numbers. ```js const { inspect } = require('node:util'); const thousand = 1_000; const million = 1_000_000; const bigNumber = 123_456_789n; const bigDecimal = 1_234.123_45; console.log(inspect(thousand, { numericSeparator: true })); // 1_000 console.log(inspect(million, { numericSeparator: true })); // 1_000_000 console.log(inspect(bigNumber, { numericSeparator: true })); // 123_456_789n console.log(inspect(bigDecimal, { numericSeparator: true })); // 1_234.123_45 ``` `util.inspect()` is a synchronous method intended for debugging. Its maximum output length is approximately 128 MiB. Inputs that result in longer output will be truncated. ### Customizing `util.inspect` colors <!-- type=misc --> Color output (if enabled) of `util.inspect` is customizable globally via the `util.inspect.styles` and `util.inspect.colors` properties. `util.inspect.styles` is a map associating a style name to a color from `util.inspect.colors`. The default styles and associated colors are: * `bigint`: `yellow` * `boolean`: `yellow` * `date`: `magenta` * `module`: `underline` * `name`: (no styling) * `null`: `bold` * `number`: `yellow` * `regexp`: `red` * `special`: `cyan` (e.g., `Proxies`) * `string`: `green` * `symbol`: `green` * `undefined`: `grey` Color styling uses ANSI control codes that may not be supported on all terminals. To verify color support use [`tty.hasColors()`][]. Predefined control codes are listed below (grouped as "Modifiers", "Foreground colors", and "Background colors"). #### Modifiers Modifier support varies throughout different terminals. They will mostly be ignored, if not supported. * `reset` - Resets all (color) modifiers to their defaults * **bold** - Make text bold * _italic_ - Make text italic * <span style="border-bottom: 1px;">underline</span> - Make text underlined * ~~strikethrough~~ - Puts a horizontal line through the center of the text (Alias: `strikeThrough`, `crossedout`, `crossedOut`) * `hidden` - Prints the text, but makes it invisible (Alias: conceal) * <span style="opacity: 0.5;">dim</span> - Decreased color intensity (Alias: `faint`) * <span style="border-top: 1px">overlined</span> - Make text overlined * blink - Hides and shows the text in an interval * <span style="filter: invert(100%)">inverse</span> - Swap foreground and background colors (Alias: `swapcolors`, `swapColors`) * <span style="border-bottom: 1px double;">doubleunderline</span> - Make text double underlined (Alias: `doubleUnderline`) * <span style="border: 1px">framed</span> - Draw a frame around the text #### Foreground colors * `black` * `red` * `green` * `yellow` * `blue` * `magenta` * `cyan` * `white` * `gray` (alias: `grey`, `blackBright`) * `redBright` * `greenBright` * `yellowBright` * `blueBright` * `magentaBright` * `cyanBright` * `whiteBright` #### Background colors * `bgBlack` * `bgRed` * `bgGreen` * `bgYellow` * `bgBlue` * `bgMagenta` * `bgCyan` * `bgWhite` * `bgGray` (alias: `bgGrey`, `bgBlackBright`) * `bgRedBright` * `bgGreenBright` * `bgYellowBright` * `bgBlueBright` * `bgMagentaBright` * `bgCyanBright` * `bgWhiteBright` ### Custom inspection functions on objects <!-- type=misc --> <!-- YAML added: v0.1.97 changes: - version: - v17.3.0 - v16.14.0 pr-url: https://github.com/nodejs/node/pull/41019 description: The inspect argument is added for more interoperability. --> Objects may also define their own [`[util.inspect.custom](depth, opts, inspect)`][util.inspect.custom] function, which `util.inspect()` will invoke and use the result of when inspecting the object. ```js const util = require('node:util'); class Box { constructor(value) { this.value = value; } [util.inspect.custom](depth, options, inspect) { if (depth < 0) { return options.stylize('[Box]', 'special'); } const newOptions = Object.assign({}, options, { depth: options.depth === null ? null : options.depth - 1, }); // Five space padding because that's the size of "Box< ". const padding = ' '.repeat(5); const inner = inspect(this.value, newOptions) .replace(/\n/g, `\n${padding}`); return `${options.stylize('Box', 'special')}< ${inner} >`; } } const box = new Box(true); util.inspect(box); // Returns: "Box< true >" ``` Custom `[util.inspect.custom](depth, opts, inspect)` functions typically return a string but may return a value of any type that will be formatted accordingly by `util.inspect()`. ```js const util = require('node:util'); const obj = { foo: 'this will not show up in the inspect() output' }; obj[util.inspect.custom] = (depth) => { return { bar: 'baz' }; }; util.inspect(obj); // Returns: "{ bar: 'baz' }" ``` ### `util.inspect.custom` <!-- YAML added: v6.6.0 changes: - version: v10.12.0 pr-url: https://github.com/nodejs/node/pull/20857 description: This is now defined as a shared symbol. --> * {symbol} that can be used to declare custom inspect functions. In addition to being accessible through `util.inspect.custom`, this symbol is [registered globally][global symbol registry] and can be accessed in any environment as `Symbol.for('nodejs.util.inspect.custom')`. Using this allows code to be written in a portable fashion, so that the custom inspect function is used in an Node.js environment and ignored in the browser. The `util.inspect()` function itself is passed as third argument to the custom inspect function to allow further portability. ```js const customInspectSymbol = Symbol.for('nodejs.util.inspect.custom'); class Password { constructor(value) { this.value = value; } toString() { return 'xxxxxxxx'; } [customInspectSymbol](depth, inspectOptions, inspect) { return `Password <${this.toString()}>`; } } const password = new Password('r0sebud'); console.log(password); // Prints Password <xxxxxxxx> ``` See [Custom inspection functions on Objects][] for more details. ### `util.inspect.defaultOptions` <!-- YAML added: v6.4.0 --> The `defaultOptions` value allows customization of the default options used by `util.inspect`. This is useful for functions like `console.log` or `util.format` which implicitly call into `util.inspect`. It shall be set to an object containing one or more valid [`util.inspect()`][] options. Setting option properties directly is also supported. ```js const util = require('node:util'); const arr = Array(101).fill(0); console.log(arr); // Logs the truncated array util.inspect.defaultOptions.maxArrayLength = null; console.log(arr); // logs the full array ``` ## `util.isDeepStrictEqual(val1, val2)` <!-- YAML added: v9.0.0 --> * `val1` {any} * `val2` {any} * Returns: {boolean} Returns `true` if there is deep strict equality between `val1` and `val2`. Otherwise, returns `false`. See [`assert.deepStrictEqual()`][] for more information about deep strict equality. ## Class: `util.MIMEType` <!-- YAML added: - v19.1.0 - v18.13.0 --> > Stability: 1 - Experimental An implementation of [the MIMEType class](https://bmeck.github.io/node-proposal-mime-api/). In accordance with browser conventions, all properties of `MIMEType` objects are implemented as getters and setters on the class prototype, rather than as data properties on the object itself. A MIME string is a structured string containing multiple meaningful components. When parsed, a `MIMEType` object is returned containing properties for each of these components. ### Constructor: `new MIMEType(input)` * `input` {string} The input MIME to parse Creates a new `MIMEType` object by parsing the `input`. ```mjs import { MIMEType } from 'node:util'; const myMIME = new MIMEType('text/plain'); ``` ```cjs const { MIMEType } = require('node:util'); const myMIME = new MIMEType('text/plain'); ``` A `TypeError` will be thrown if the `input` is not a valid MIME. Note that an effort will be made to coerce the given values into strings. For instance: ```mjs import { MIMEType } from 'node:util'; const myMIME = new MIMEType({ toString: () => 'text/plain' }); console.log(String(myMIME)); // Prints: text/plain ``` ```cjs const { MIMEType } = require('node:util'); const myMIME = new MIMEType({ toString: () => 'text/plain' }); console.log(String(myMIME)); // Prints: text/plain ``` ### `mime.type` * {string} Gets and sets the type portion of the MIME. ```mjs import { MIMEType } from 'node:util'; const myMIME = new MIMEType('text/javascript'); console.log(myMIME.type); // Prints: text myMIME.type = 'application'; console.log(myMIME.type); // Prints: application console.log(String(myMIME)); // Prints: application/javascript ``` ```cjs const { MIMEType } = require('node:util'); const myMIME = new MIMEType('text/javascript'); console.log(myMIME.type); // Prints: text myMIME.type = 'application'; console.log(myMIME.type); // Prints: application console.log(String(myMIME)); // Prints: application/javascript ``` ### `mime.subtype` * {string} Gets and sets the subtype portion of the MIME. ```mjs import { MIMEType } from 'node:util'; const myMIME = new MIMEType('text/ecmascript'); console.log(myMIME.subtype); // Prints: ecmascript myMIME.subtype = 'javascript'; console.log(myMIME.subtype); // Prints: javascript console.log(String(myMIME)); // Prints: text/javascript ``` ```cjs const { MIMEType } = require('node:util'); const myMIME = new MIMEType('text/ecmascript'); console.log(myMIME.subtype); // Prints: ecmascript myMIME.subtype = 'javascript'; console.log(myMIME.subtype); // Prints: javascript console.log(String(myMIME)); // Prints: text/javascript ``` ### `mime.essence` * {string} Gets the essence of the MIME. This property is read only. Use `mime.type` or `mime.subtype` to alter the MIME. ```mjs import { MIMEType } from 'node:util'; const myMIME = new MIMEType('text/javascript;key=value'); console.log(myMIME.essence); // Prints: text/javascript myMIME.type = 'application'; console.log(myMIME.essence); // Prints: application/javascript console.log(String(myMIME)); // Prints: application/javascript;key=value ``` ```cjs const { MIMEType } = require('node:util'); const myMIME = new MIMEType('text/javascript;key=value'); console.log(myMIME.essence); // Prints: text/javascript myMIME.type = 'application'; console.log(myMIME.essence); // Prints: application/javascript console.log(String(myMIME)); // Prints: application/javascript;key=value ``` ### `mime.params` * {MIMEParams} Gets the [`MIMEParams`][] object representing the parameters of the MIME. This property is read-only. See [`MIMEParams`][] documentation for details. ### `mime.toString()` * Returns: {string} The `toString()` method on the `MIMEType` object returns the serialized MIME. Because of the need for standard compliance, this method does not allow users to customize the serialization process of the MIME. ### `mime.toJSON()` * Returns: {string} Alias for [`mime.toString()`][]. This method is automatically called when an `MIMEType` object is serialized with [`JSON.stringify()`][]. ```mjs import { MIMEType } from 'node:util'; const myMIMES = [ new MIMEType('image/png'), new MIMEType('image/gif'), ]; console.log(JSON.stringify(myMIMES)); // Prints: ["image/png", "image/gif"] ``` ```cjs const { MIMEType } = require('node:util'); const myMIMES = [ new MIMEType('image/png'), new MIMEType('image/gif'), ]; console.log(JSON.stringify(myMIMES)); // Prints: ["image/png", "image/gif"] ``` ## Class: `util.MIMEParams` <!-- YAML added: - v19.1.0 - v18.13.0 --> The `MIMEParams` API provides read and write access to the parameters of a `MIMEType`. ### Constructor: `new MIMEParams()` Creates a new `MIMEParams` object by with empty parameters ```mjs import { MIMEParams } from 'node:util'; const myParams = new MIMEParams(); ``` ```cjs const { MIMEParams } = require('node:util'); const myParams = new MIMEParams(); ``` ### `mimeParams.delete(name)` * `name` {string} Remove all name-value pairs whose name is `name`. ### `mimeParams.entries()` * Returns: {Iterator} Returns an iterator over each of the name-value pairs in the parameters. Each item of the iterator is a JavaScript `Array`. The first item of the array is the `name`, the second item of the array is the `value`. ### `mimeParams.get(name)` * `name` {string} * Returns: {string | null} A string or `null` if there is no name-value pair with the given `name`. Returns the value of the first name-value pair whose name is `name`. If there are no such pairs, `null` is returned. ### `mimeParams.has(name)` * `name` {string} * Returns: {boolean} Returns `true` if there is at least one name-value pair whose name is `name`. ### `mimeParams.keys()` * Returns: {Iterator} Returns an iterator over the names of each name-value pair. ```mjs import { MIMEType } from 'node:util'; const { params } = new MIMEType('text/plain;foo=0;bar=1'); for (const name of params.keys()) { console.log(name); } // Prints: // foo // bar ``` ```cjs const { MIMEType } = require('node:util'); const { params } = new MIMEType('text/plain;foo=0;bar=1'); for (const name of params.keys()) { console.log(name); } // Prints: // foo // bar ``` ### `mimeParams.set(name, value)` * `name` {string} * `value` {string} Sets the value in the `MIMEParams` object associated with `name` to `value`. If there are any pre-existing name-value pairs whose names are `name`, set the first such pair's value to `value`. ```mjs import { MIMEType } from 'node:util'; const { params } = new MIMEType('text/plain;foo=0;bar=1'); params.set('foo', 'def'); params.set('baz', 'xyz'); console.log(params.toString()); // Prints: foo=def;bar=1;baz=xyz ``` ```cjs const { MIMEType } = require('node:util'); const { params } = new MIMEType('text/plain;foo=0;bar=1'); params.set('foo', 'def'); params.set('baz', 'xyz'); console.log(params.toString()); // Prints: foo=def;bar=1;baz=xyz ``` ### `mimeParams.values()` * Returns: {Iterator} Returns an iterator over the values of each name-value pair. ### `mimeParams[@@iterator]()` * Returns: {Iterator} Alias for [`mimeParams.entries()`][]. ```mjs import { MIMEType } from 'node:util'; const { params } = new MIMEType('text/plain;foo=bar;xyz=baz'); for (const [name, value] of params) { console.log(name, value); } // Prints: // foo bar // xyz baz ``` ```cjs const { MIMEType } = require('node:util'); const { params } = new MIMEType('text/plain;foo=bar;xyz=baz'); for (const [name, value] of params) { console.log(name, value); } // Prints: // foo bar // xyz baz ``` ## `util.parseArgs([config])` <!-- YAML added: - v18.3.0 - v16.17.0 changes: - version: v20.16.0 pr-url: https://github.com/nodejs/node/pull/53107 description: add support for allowing negative options in input `config`. - version: - v20.0.0 pr-url: https://github.com/nodejs/node/pull/46718 description: The API is no longer experimental. - version: - v18.11.0 - v16.19.0 pr-url: https://github.com/nodejs/node/pull/44631 description: Add support for default values in input `config`. - version: - v18.7.0 - v16.17.0 pr-url: https://github.com/nodejs/node/pull/43459 description: add support for returning detailed parse information using `tokens` in input `config` and returned properties. --> * `config` {Object} Used to provide arguments for parsing and to configure the parser. `config` supports the following properties: * `args` {string\[]} array of argument strings. **Default:** `process.argv` with `execPath` and `filename` removed. * `options` {Object} Used to describe arguments known to the parser. Keys of `options` are the long names of options and values are an {Object} accepting the following properties: * `type` {string} Type of argument, which must be either `boolean` or `string`. * `multiple` {boolean} Whether this option can be provided multiple times. If `true`, all values will be collected in an array. If `false`, values for the option are last-wins. **Default:** `false`. * `short` {string} A single character alias for the option. * `default` {string | boolean | string\[] | boolean\[]} The default option value when it is not set by args. It must be of the same type as the `type` property. When `multiple` is `true`, it must be an array. * `strict` {boolean} Should an error be thrown when unknown arguments are encountered, or when arguments are passed that do not match the `type` configured in `options`. **Default:** `true`. * `allowPositionals` {boolean} Whether this command accepts positional arguments. **Default:** `false` if `strict` is `true`, otherwise `true`. * `allowNegative` {boolean} If `true`, allows explicitly setting boolean options to `false` by prefixing the option name with `--no-`. **Default:** `false`. * `tokens` {boolean} 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. **Default:** `false`. * Returns: {Object} The parsed command line arguments: * `values` {Object} A mapping of parsed option names with their {string} or {boolean} values. * `positionals` {string\[]} Positional arguments. * `tokens` {Object\[] | undefined} See [parseArgs tokens](#parseargs-tokens) section. Only returned if `config` includes `tokens: true`. Provides a higher level API for command-line argument parsing than interacting with `process.argv` directly. Takes a specification for the expected arguments and returns a structured object with the parsed options and positionals. ```mjs import { parseArgs } from 'node:util'; const args = ['-f', '--bar', 'b']; const options = { foo: { type: 'boolean', short: 'f', }, bar: { type: 'string', }, }; const { values, positionals, } = parseArgs({ args, options }); console.log(values, positionals); // Prints: [Object: null prototype] { foo: true, bar: 'b' } [] ``` ```cjs const { parseArgs } = require('node:util'); const args = ['-f', '--bar', 'b']; const options = { foo: { type: 'boolean', short: 'f', }, bar: { type: 'string', }, }; const { values, positionals, } = parseArgs({ args, options }); console.log(values, positionals); // Prints: [Object: null prototype] { foo: true, bar: 'b' } [] ``` ### `parseArgs` `tokens` Detailed parse information is available for adding custom behaviors by specifying `tokens: true` in the configuration. The returned tokens have properties describing: * all tokens * `kind` {string} One of 'option', 'positional', or 'option-terminator'. * `index` {number} Index of element in `args` containing token. So the source argument for a token is `args[token.index]`. * option tokens * `name` {string} Long name of option. * `rawName` {string} How option used in args, like `-f` of `--foo`. * `value` {string | undefined} Option value specified in args. Undefined for boolean options. * `inlineValue` {boolean | undefined} Whether option value specified inline, like `--foo=bar`. * positional tokens * `value` {string} The value of the positional argument in args (i.e. `args[index]`). * option-terminator token 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 `-xy` expand to a token for each option. So `-xxx` produces three tokens. For example, to add support for a negated option like `--no-color` (which `allowNegative` supports when the option is of `boolean` type), the returned tokens can be reprocessed to change the value stored for the negated option. ```mjs import { parseArgs } from 'node:util'; const options = { 'color': { type: 'boolean' }, 'no-color': { type: 'boolean' }, 'logfile': { type: 'string' }, 'no-logfile': { type: 'boolean' }, }; const { values, tokens } = parseArgs({ options, tokens: true }); // Reprocess the option tokens and overwrite the returned values. tokens .filter((token) => token.kind === 'option') .forEach((token) => { if (token.name.startsWith('no-')) { // Store foo:false for --no-foo const positiveName = token.name.slice(3); values[positiveName] = false; delete values[token.name]; } else { // Resave value so last one wins if both --foo and --no-foo. values[token.name] = token.value ?? true; } }); const color = values.color; const logfile = values.logfile ?? 'default.log'; console.log({ logfile, color }); ``` ```cjs const { parseArgs } = require('node:util'); const options = { 'color': { type: 'boolean' }, 'no-color': { type: 'boolean' }, 'logfile': { type: 'string' }, 'no-logfile': { type: 'boolean' }, }; const { values, tokens } = parseArgs({ options, tokens: true }); // Reprocess the option tokens and overwrite the returned values. tokens .filter((token) => token.kind === 'option') .forEach((token) => { if (token.name.startsWith('no-')) { // Store foo:false for --no-foo const positiveName = token.name.slice(3); values[positiveName] = false; delete values[token.name]; } else { // Resave value so last one wins if both --foo and --no-foo. values[token.name] = token.value ?? true; } }); const color = values.color; const logfile = values.logfile ?? 'default.log'; console.log({ logfile, color }); ``` Example usage showing negated options, and when an option is used multiple ways then last one wins. ```console $ node negate.js { logfile: 'default.log', color: undefined } $ node negate.js --no-logfile --no-color { logfile: false, color: false } $ node negate.js --logfile=test.log --color { logfile: 'test.log', color: true } $ node negate.js --no-logfile --logfile=test.log --color --no-color { logfile: 'test.log', color: false } ``` ## `util.parseEnv(content)` > Stability: 1.1 - Active development <!-- YAML added: v20.12.0 --> * `content` {string} The raw contents of a `.env` file. * Returns: {Object} Given an example `.env` file: ```cjs const { parseEnv } = require('node:util'); parseEnv('HELLO=world\nHELLO=oh my\n'); // Returns: { HELLO: 'oh my' } ``` ```mjs import { parseEnv } from 'node:util'; parseEnv('HELLO=world\nHELLO=oh my\n'); // Returns: { HELLO: 'oh my' } ``` ## `util.promisify(original)` <!-- YAML added: v8.0.0 changes: - version: v20.8.0 pr-url: https://github.com/nodejs/node/pull/49647 description: Calling `promisify` on a function that returns a `Promise` is deprecated. --> * `original` {Function} * Returns: {Function} Takes a function following the common error-first callback style, i.e. taking an `(err, value) => ...` callback as the last argument, and returns a version that returns promises. ```js const util = require('node:util'); const fs = require('node:fs'); const stat = util.promisify(fs.stat); stat('.').then((stats) => { // Do something with `stats` }).catch((error) => { // Handle the error. }); ``` Or, equivalently using `async function`s: ```js const util = require('node:util'); const fs = require('node:fs'); const stat = util.promisify(fs.stat); async function callStat() { const stats = await stat('.'); console.log(`This directory is owned by ${stats.uid}`); } callStat(); ``` If there is an `original[util.promisify.custom]` property present, `promisify` will return its value, see [Custom promisified functions][]. `promisify()` assumes that `original` is a function taking a callback as its final argument in all cases. If `original` is not a function, `promisify()` will throw an error. If `original` 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. Using `promisify()` on class methods or other methods that use `this` may not work as expected unless handled specially: ```js const util = require('node:util'); class Foo { constructor() { this.a = 42; } bar(callback) { callback(null, this.a); } } const foo = new Foo(); const naiveBar = util.promisify(foo.bar); // TypeError: Cannot read property 'a' of undefined // naiveBar().then(a => console.log(a)); naiveBar.call(foo).then((a) => console.log(a)); // '42' const bindBar = naiveBar.bind(foo); bindBar().then((a) => console.log(a)); // '42' ``` ### Custom promisified functions Using the `util.promisify.custom` symbol one can override the return value of [`util.promisify()`][]: ```js const util = require('node:util'); function doSomething(foo, callback) { // ... } doSomething[util.promisify.custom] = (foo) => { return getPromiseSomehow(); }; const promisified = util.promisify(doSomething); console.log(promisified === doSomething[util.promisify.custom]); // prints 'true' ``` 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. For example, with a function that takes in `(foo, onSuccessCallback, onErrorCallback)`: ```js doSomething[util.promisify.custom] = (foo) => { return new Promise((resolve, reject) => { doSomething(foo, resolve, reject); }); }; ``` If `promisify.custom` is defined but is not a function, `promisify()` will throw an error. ### `util.promisify.custom` <!-- YAML added: v8.0.0 changes: - version: - v13.12.0 - v12.16.2 pr-url: https://github.com/nodejs/node/pull/31672 description: This is now defined as a shared symbol. --> * {symbol} that can be used to declare custom promisified variants of functions, see [Custom promisified functions][]. In addition to being accessible through `util.promisify.custom`, this symbol is [registered globally][global symbol registry] and can be accessed in any environment as `Symbol.for('nodejs.util.promisify.custom')`. For example, with a function that takes in `(foo, onSuccessCallback, onErrorCallback)`: ```js const kCustomPromisifiedSymbol = Symbol.for('nodejs.util.promisify.custom'); doSomething[kCustomPromisifiedSymbol] = (foo) => { return new Promise((resolve, reject) => { doSomething(foo, resolve, reject); }); }; ``` ## `util.stripVTControlCharacters(str)` <!-- YAML added: v16.11.0 --> * `str` {string} * Returns: {string} Returns `str` with any ANSI escape codes removed. ```js console.log(util.stripVTControlCharacters('\u001B[4mvalue\u001B[0m')); // Prints "value" ``` ## `util.styleText(format, text[, options])` > Stability: 1.1 - Active development <!-- YAML added: v20.12.0 changes: - version: v20.18.0 pr-url: https://github.com/nodejs/node/pull/54389 description: Respect isTTY and environment variables such as NO_COLORS, NODE_DISABLE_COLORS, and FORCE_COLOR. --> * `format` {string | Array} A text format or an Array of text formats defined in `util.inspect.colors`. * `text` {string} The text to to be formatted. * `options` {Object} * `validateStream` {boolean} When true, `stream` is checked to see if it can handle colors. **Default:** `true`. * `stream` {Stream} A stream that will be validated if it can be colored. **Default:** `process.stdout`. This function returns a formatted text considering the `format` passed for printing in a terminal. It is aware of the terminal's capabilities and acts according to the configuration set via `NO_COLORS`, `NODE_DISABLE_COLORS` and `FORCE_COLOR` environment variables. ```mjs import { styleText } from 'node:util'; import { stderr } from 'node:process'; const successMessage = styleText('green', 'Success!'); console.log(successMessage); const errorMessage = styleText( 'red', 'Error! Error!', // Validate if process.stderr has TTY { stream: stderr }, ); console.error(successMessage); ``` ```cjs const { styleText } = require('node:util'); const { stderr } = require('node:process'); const successMessage = styleText('green', 'Success!'); console.log(successMessage); const errorMessage = styleText( 'red', 'Error! Error!', // Validate if process.stderr has TTY { stream: stderr }, ); console.error(successMessage); ``` `util.inspect.colors` also provides text formats such as `italic`, and `underline` and you can combine both: ```cjs console.log( util.styleText(['underline', 'italic'], 'My italic underlined message'), ); ``` 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. ```cjs console.log( util.styleText(['red', 'green'], 'text'), // green ); ``` The full list of formats can be found in [modifiers][]. ## Class: `util.TextDecoder` <!-- YAML added: v8.3.0 --> An implementation of the [WHATWG Encoding Standard][] `TextDecoder` API. ```js const decoder = new TextDecoder(); const u8arr = new Uint8Array([72, 101, 108, 108, 111]); console.log(decoder.decode(u8arr)); // Hello ``` ### WHATWG supported encodings Per the [WHATWG Encoding Standard][], the encodings supported by the `TextDecoder` API are outlined in the tables below. For each encoding, one or more aliases may be used. Different Node.js build configurations support different sets of encodings. (see [Internationalization][]) #### Encodings supported by default (with full ICU data) | Encoding | Aliases | | ------------------ | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | `'ibm866'` | `'866'`, `'cp866'`, `'csibm866'` | | `'iso-8859-2'` | `'csisolatin2'`, `'iso-ir-101'`, `'iso8859-2'`, `'iso88592'`, `'iso_8859-2'`, `'iso_8859-2:1987'`, `'l2'`, `'latin2'` | | `'iso-8859-3'` | `'csisolatin3'`, `'iso-ir-109'`, `'iso8859-3'`, `'iso88593'`, `'iso_8859-3'`, `'iso_8859-3:1988'`, `'l3'`, `'latin3'` | | `'iso-8859-4'` | `'csisolatin4'`, `'iso-ir-110'`, `'iso8859-4'`, `'iso88594'`, `'iso_8859-4'`, `'iso_8859-4:1988'`, `'l4'`, `'latin4'` | | `'iso-8859-5'` | `'csisolatincyrillic'`, `'cyrillic'`, `'iso-ir-144'`, `'iso8859-5'`, `'iso88595'`, `'iso_8859-5'`, `'iso_8859-5:1988'` | | `'iso-8859-6'` | `'arabic'`, `'asmo-708'`, `'csiso88596e'`, `'csiso88596i'`, `'csisolatinarabic'`, `'ecma-114'`, `'iso-8859-6-e'`, `'iso-8859-6-i'`, `'iso-ir-127'`, `'iso8859-6'`, `'iso88596'`, `'iso_8859-6'`, `'iso_8859-6:1987'` | | `'iso-8859-7'` | `'csisolatingreek'`, `'ecma-118'`, `'elot_928'`, `'greek'`, `'greek8'`, `'iso-ir-126'`, `'iso8859-7'`, `'iso88597'`, `'iso_8859-7'`, `'iso_8859-7:1987'`, `'sun_eu_greek'` | | `'iso-8859-8'` | `'csiso88598e'`, `'csisolatinhebrew'`, `'hebrew'`, `'iso-8859-8-e'`, `'iso-ir-138'`, `'iso8859-8'`, `'iso88598'`, `'iso_8859-8'`, `'iso_8859-8:1988'`, `'visual'` | | `'iso-8859-8-i'` | `'csiso88598i'`, `'logical'` | | `'iso-8859-10'` | `'csisolatin6'`, `'iso-ir-157'`, `'iso8859-10'`, `'iso885910'`, `'l6'`, `'latin6'` | | `'iso-8859-13'` | `'iso8859-13'`, `'iso885913'` | | `'iso-8859-14'` | `'iso8859-14'`, `'iso885914'` | | `'iso-8859-15'` | `'csisolatin9'`, `'iso8859-15'`, `'iso885915'`, `'iso_8859-15'`, `'l9'` | | `'koi8-r'` | `'cskoi8r'`, `'koi'`, `'koi8'`, `'koi8_r'` | | `'koi8-u'` | `'koi8-ru'` | | `'macintosh'` | `'csmacintosh'`, `'mac'`, `'x-mac-roman'` | | `'windows-874'` | `'dos-874'`, `'iso-8859-11'`, `'iso8859-11'`, `'iso885911'`, `'tis-620'` | | `'windows-1250'` | `'cp1250'`, `'x-cp1250'` | | `'windows-1251'` | `'cp1251'`, `'x-cp1251'` | | `'windows-1252'` | `'ansi_x3.4-1968'`, `'ascii'`, `'cp1252'`, `'cp819'`, `'csisolatin1'`, `'ibm819'`, `'iso-8859-1'`, `'iso-ir-100'`, `'iso8859-1'`, `'iso88591'`, `'iso_8859-1'`, `'iso_8859-1:1987'`, `'l1'`, `'latin1'`, `'us-ascii'`, `'x-cp1252'` | | `'windows-1253'` | `'cp1253'`, `'x-cp1253'` | | `'windows-1254'` | `'cp1254'`, `'csisolatin5'`, `'iso-8859-9'`, `'iso-ir-148'`, `'iso8859-9'`, `'iso88599'`, `'iso_8859-9'`, `'iso_8859-9:1989'`, `'l5'`, `'latin5'`, `'x-cp1254'` | | `'windows-1255'` | `'cp1255'`, `'x-cp1255'` | | `'windows-1256'` | `'cp1256'`, `'x-cp1256'` | | `'windows-1257'` | `'cp1257'`, `'x-cp1257'` | | `'windows-1258'` | `'cp1258'`, `'x-cp1258'` | | `'x-mac-cyrillic'` | `'x-mac-ukrainian'` | | `'gbk'` | `'chinese'`, `'csgb2312'`, `'csiso58gb231280'`, `'gb2312'`, `'gb_2312'`, `'gb_2312-80'`, `'iso-ir-58'`, `'x-gbk'` | | `'gb18030'` | | | `'big5'` | `'big5-hkscs'`, `'cn-big5'`, `'csbig5'`, `'x-x-big5'` | | `'euc-jp'` | `'cseucpkdfmtjapanese'`, `'x-euc-jp'` | | `'iso-2022-jp'` | `'csiso2022jp'` | | `'shift_jis'` | `'csshiftjis'`, `'ms932'`, `'ms_kanji'`, `'shift-jis'`, `'sjis'`, `'windows-31j'`, `'x-sjis'` | | `'euc-kr'` | `'cseuckr'`, `'csksc56011987'`, `'iso-ir-149'`, `'korean'`, `'ks_c_5601-1987'`, `'ks_c_5601-1989'`, `'ksc5601'`, `'ksc_5601'`, `'windows-949'` | #### Encodings supported when Node.js is built with the `small-icu` option | Encoding | Aliases | | ------------ | ------------------------------- | | `'utf-8'` | `'unicode-1-1-utf-8'`, `'utf8'` | | `'utf-16le'` | `'utf-16'` | | `'utf-16be'` | | #### Encodings supported when ICU is disabled | Encoding | Aliases | | ------------ | ------------------------------- | | `'utf-8'` | `'unicode-1-1-utf-8'`, `'utf8'` | | `'utf-16le'` | `'utf-16'` | The `'iso-8859-16'` encoding listed in the [WHATWG Encoding Standard][] is not supported. ### `new TextDecoder([encoding[, options]])` <!-- YAML added: v8.3.0 changes: - version: v11.0.0 pr-url: https://github.com/nodejs/node/pull/22281 description: The class is now available on the global object. --> * `encoding` {string} Identifies the `encoding` that this `TextDecoder` instance supports. **Default:** `'utf-8'`. * `options` {Object} * `fatal` {boolean} `true` if decoding failures are fatal. This option is not supported when ICU is disabled (see [Internationalization][]). **Default:** `false`. * `ignoreBOM` {boolean} When `true`, the `TextDecoder` will include the byte order mark in the decoded result. When `false`, the byte order mark will be removed from the output. This option is only used when `encoding` is `'utf-8'`, `'utf-16be'`, or `'utf-16le'`. **Default:** `false`. Creates a new `TextDecoder` instance. The `encoding` may specify one of the supported encodings or an alias. The `TextDecoder` class is also available on the global object. ### `textDecoder.decode([input[, options]])` * `input` {ArrayBuffer|DataView|TypedArray} An `ArrayBuffer`, `DataView`, or `TypedArray` instance containing the encoded data. * `options` {Object} * `stream` {boolean} `true` if additional chunks of data are expected. **Default:** `false`. * Returns: {string} Decodes the `input` and returns a string. If `options.stream` is `true`, any incomplete byte sequences occurring at the end of the `input` are buffered internally and emitted after the next call to `textDecoder.decode()`. If `textDecoder.fatal` is `true`, decoding errors that occur will result in a `TypeError` being thrown. ### `textDecoder.encoding` * {string} The encoding supported by the `TextDecoder` instance. ### `textDecoder.fatal` * {boolean} The value will be `true` if decoding errors result in a `TypeError` being thrown. ### `textDecoder.ignoreBOM` * {boolean} The value will be `true` if the decoding result will include the byte order mark. ## Class: `util.TextEncoder` <!-- YAML added: v8.3.0 changes: - version: v11.0.0 pr-url: https://github.com/nodejs/node/pull/22281 description: The class is now available on the global object. --> An implementation of the [WHATWG Encoding Standard][] `TextEncoder` API. All instances of `TextEncoder` only support UTF-8 encoding. ```js const encoder = new TextEncoder(); const uint8array = encoder.encode('this is some data'); ``` The `TextEncoder` class is also available on the global object. ### `textEncoder.encode([input])` * `input` {string} The text to encode. **Default:** an empty string. * Returns: {Uint8Array} UTF-8 encodes the `input` string and returns a `Uint8Array` containing the encoded bytes. ### `textEncoder.encodeInto(src, dest)` * `src` {string} The text to encode. * `dest` {Uint8Array} The array to hold the encode result. * Returns: {Object} * `read` {number} The read Unicode code units of src. * `written` {number} The written UTF-8 bytes of dest. UTF-8 encodes the `src` string to the `dest` Uint8Array and returns an object containing the read Unicode code units and written UTF-8 bytes. ```js const encoder = new TextEncoder(); const src = 'this is some data'; const dest = new Uint8Array(10); const { read, written } = encoder.encodeInto(src, dest); ``` ### `textEncoder.encoding` * {string} The encoding supported by the `TextEncoder` instance. Always set to `'utf-8'`. ## `util.toUSVString(string)` <!-- YAML added: - v16.8.0 - v14.18.0 --> * `string` {string} Returns the `string` after replacing any surrogate code points (or equivalently, any unpaired surrogate code units) with the Unicode "replacement character" U+FFFD. ## `util.transferableAbortController()` <!-- YAML added: v18.11.0 --> > Stability: 1 - Experimental Creates and returns an {AbortController} instance whose {AbortSignal} is marked as transferable and can be used with `structuredClone()` or `postMessage()`. ## `util.transferableAbortSignal(signal)` <!-- YAML added: v18.11.0 --> > Stability: 1 - Experimental * `signal` {AbortSignal} * Returns: {AbortSignal} Marks the given {AbortSignal} as transferable so that it can be used with `structuredClone()` and `postMessage()`. ```js const signal = transferableAbortSignal(AbortSignal.timeout(100)); const channel = new MessageChannel(); channel.port2.postMessage(signal, [signal]); ``` ## `util.aborted(signal, resource)` <!-- YAML added: v19.7.0 --> > Stability: 1 - Experimental * `signal` {AbortSignal} * `resource` {Object} Any non-null entity, reference to which is held weakly. * Returns: {Promise} Listens to abort event on the provided `signal` and returns a promise that is fulfilled when the `signal` is aborted. If the passed `resource` is garbage collected before the `signal` is aborted, the returned promise shall remain pending indefinitely. ```cjs const { aborted } = require('node:util'); const dependent = obtainSomethingAbortable(); aborted(dependent.signal, dependent).then(() => { // Do something when dependent is aborted. }); dependent.on('event', () => { dependent.abort(); }); ``` ```mjs import { aborted } from 'node:util'; const dependent = obtainSomethingAbortable(); aborted(dependent.signal, dependent).then(() => { // Do something when dependent is aborted. }); dependent.on('event', () => { dependent.abort(); }); ``` ## `util.types` <!-- YAML added: v10.0.0 changes: - version: v15.3.0 pr-url: https://github.com/nodejs/node/pull/34055 description: Exposed as `require('util/types')`. --> `util.types` provides type checks for different kinds of built-in objects. Unlike `instanceof` or `Object.prototype.toString.call(value)`, 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++. 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. The API is accessible via `require('node:util').types` or `require('node:util/types')`. ### `util.types.isAnyArrayBuffer(value)` <!-- YAML added: v10.0.0 --> * `value` {any} * Returns: {boolean} Returns `true` if the value is a built-in [`ArrayBuffer`][] or [`SharedArrayBuffer`][] instance. See also [`util.types.isArrayBuffer()`][] and [`util.types.isSharedArrayBuffer()`][]. ```js util.types.isAnyArrayBuffer(new ArrayBuffer()); // Returns true util.types.isAnyArrayBuffer(new SharedArrayBuffer()); // Returns true ``` ### `util.types.isArrayBufferView(value)` <!-- YAML added: v10.0.0 --> * `value` {any} * Returns: {boolean} Returns `true` if the value is an instance of one of the [`ArrayBuffer`][] views, such as typed array objects or [`DataView`][]. Equivalent to [`ArrayBuffer.isView()`][]. ```js util.types.isArrayBufferView(new Int8Array()); // true util.types.isArrayBufferView(Buffer.from('hello world')); // true util.types.isArrayBufferView(new DataView(new ArrayBuffer(16))); // true util.types.isArrayBufferView(new ArrayBuffer()); // false ``` ### `util.types.isArgumentsObject(value)` <!-- YAML added: v10.0.0 --> * `value` {any} * Returns: {boolean} Returns `true` if the value is an `arguments` object. <!-- eslint-disable prefer-rest-params --> ```js function foo() { util.types.isArgumentsObject(arguments); // Returns true } ``` ### `util.types.isArrayBuffer(value)` <!-- YAML added: v10.0.0 --> * `value` {any} * Returns: {boolean} Returns `true` if the value is a built-in [`ArrayBuffer`][] instance. This does _not_ include [`SharedArrayBuffer`][] instances. Usually, it is desirable to test for both; See [`util.types.isAnyArrayBuffer()`][] for that. ```js util.types.isArrayBuffer(new ArrayBuffer()); // Returns true util.types.isArrayBuffer(new SharedArrayBuffer()); // Returns false ``` ### `util.types.isAsyncFunction(value)` <!-- YAML added: v10.0.0 --> * `value` {any} * Returns: {boolean} Returns `true` if the value is an [async 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. ```js util.types.isAsyncFunction(function foo() {}); // Returns false util.types.isAsyncFunction(async function foo() {}); // Returns true ``` ### `util.types.isBigInt64Array(value)` <!-- YAML added: v10.0.0 --> * `value` {any} * Returns: {boolean} Returns `true` if the value is a `BigInt64Array` instance. ```js util.types.isBigInt64Array(new BigInt64Array()); // Returns true util.types.isBigInt64Array(new BigUint64Array()); // Returns false ``` ### `util.types.isBigUint64Array(value)` <!-- YAML added: v10.0.0 --> * `value` {any} * Returns: {boolean} Returns `true` if the value is a `BigUint64Array` instance. ```js util.types.isBigUint64Array(new BigInt64Array()); // Returns false util.types.isBigUint64Array(new BigUint64Array()); // Returns true ``` ### `util.types.isBooleanObject(value)` <!-- YAML added: v10.0.0 --> * `value` {any} * Returns: {boolean} Returns `true` if the value is a boolean object, e.g. created by `new Boolean()`. ```js util.types.isBooleanObject(false); // Returns false util.types.isBooleanObject(true); // Returns false util.types.isBooleanObject(new Boolean(false)); // Returns true util.types.isBooleanObject(new Boolean(true)); // Returns true util.types.isBooleanObject(Boolean(false)); // Returns false util.types.isBooleanObject(Boolean(true)); // Returns false ``` ### `util.types.isBoxedPrimitive(value)` <!-- YAML added: v10.11.0 --> * `value` {any} * Returns: {boolean} Returns `true` if the value is any boxed primitive object, e.g. created by `new Boolean()`, `new String()` or `Object(Symbol())`. For example: ```js util.types.isBoxedPrimitive(false); // Returns false util.types.isBoxedPrimitive(new Boolean(false)); // Returns true util.types.isBoxedPrimitive(Symbol('foo')); // Returns false util.types.isBoxedPrimitive(Object(Symbol('foo'))); // Returns true util.types.isBoxedPrimitive(Object(BigInt(5))); // Returns true ``` ### `util.types.isCryptoKey(value)` <!-- YAML added: v16.2.0 --> * `value` {Object} * Returns: {boolean} Returns `true` if `value` is a {CryptoKey}, `false` otherwise. ### `util.types.isDataView(value)` <!-- YAML added: v10.0.0 --> * `value` {any} * Returns: {boolean} Returns `true` if the value is a built-in [`DataView`][] instance. ```js const ab = new ArrayBuffer(20); util.types.isDataView(new DataView(ab)); // Returns true util.types.isDataView(new Float64Array()); // Returns false ``` See also [`ArrayBuffer.isView()`][]. ### `util.types.isDate(value)` <!-- YAML added: v10.0.0 --> * `value` {any} * Returns: {boolean} Returns `true` if the value is a built-in [`Date`][] instance. ```js util.types.isDate(new Date()); // Returns true ``` ### `util.types.isExternal(value)` <!-- YAML added: v10.0.0 --> * `value` {any} * Returns: {boolean} Returns `true` if the value is a native `External` value. A native `External` value is a special type of object that contains a raw C++ pointer (`void*`) 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 [frozen][`Object.freeze()`] objects with a `null` prototype. ```c #include <js_native_api.h> #include <stdlib.h> napi_value result; static napi_value MyNapi(napi_env env, napi_callback_info info) { int* raw = (int*) malloc(1024); napi_status status = napi_create_external(env, (void*) raw, NULL, NULL, &result); if (status != napi_ok) { napi_throw_error(env, NULL, "napi_create_external failed"); return NULL; } return result; } ... DECLARE_NAPI_PROPERTY("myNapi", MyNapi) ... ``` ```js const native = require('napi_addon.node'); const data = native.myNapi(); util.types.isExternal(data); // returns true util.types.isExternal(0); // returns false util.types.isExternal(new String('foo')); // returns false ``` For further information on `napi_create_external`, refer to [`napi_create_external()`][]. ### `util.types.isFloat32Array(value)` <!-- YAML added: v10.0.0 --> * `value` {any} * Returns: {boolean} Returns `true` if the value is a built-in [`Float32Array`][] instance. ```js util.types.isFloat32Array(new ArrayBuffer()); // Returns false util.types.isFloat32Array(new Float32Array()); // Returns true util.types.isFloat32Array(new Float64Array()); // Returns false ``` ### `util.types.isFloat64Array(value)` <!-- YAML added: v10.0.0 --> * `value` {any} * Returns: {boolean} Returns `true` if the value is a built-in [`Float64Array`][] instance. ```js util.types.isFloat64Array(new ArrayBuffer()); // Returns false util.types.isFloat64Array(new Uint8Array()); // Returns false util.types.isFloat64Array(new Float64Array()); // Returns true ``` ### `util.types.isGeneratorFunction(value)` <!-- YAML added: v10.0.0 --> * `value` {any} * Returns: {boolean} Returns `true` 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. ```js util.types.isGeneratorFunction(function foo() {}); // Returns false util.types.isGeneratorFunction(function* foo() {}); // Returns true ``` ### `util.types.isGeneratorObject(value)` <!-- YAML added: v10.0.0 --> * `value` {any} * Returns: {boolean} Returns `true` 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. ```js function* foo() {} const generator = foo(); util.types.isGeneratorObject(generator); // Returns true ``` ### `util.types.isInt8Array(value)` <!-- YAML added: v10.0.0 --> * `value` {any} * Returns: {boolean} Returns `true` if the value is a built-in [`Int8Array`][] instance. ```js util.types.isInt8Array(new ArrayBuffer()); // Returns false util.types.isInt8Array(new Int8Array()); // Returns true util.types.isInt8Array(new Float64Array()); // Returns false ``` ### `util.types.isInt16Array(value)` <!-- YAML added: v10.0.0 --> * `value` {any} * Returns: {boolean} Returns `true` if the value is a built-in [`Int16Array`][] instance. ```js util.types.isInt16Array(new ArrayBuffer()); // Returns false util.types.isInt16Array(new Int16Array()); // Returns true util.types.isInt16Array(new Float64Array()); // Returns false ``` ### `util.types.isInt32Array(value)` <!-- YAML added: v10.0.0 --> * `value` {any} * Returns: {boolean} Returns `true` if the value is a built-in [`Int32Array`][] instance. ```js util.types.isInt32Array(new ArrayBuffer()); // Returns false util.types.isInt32Array(new Int32Array()); // Returns true util.types.isInt32Array(new Float64Array()); // Returns false ``` ### `util.types.isKeyObject(value)` <!-- YAML added: v16.2.0 --> * `value` {Object} * Returns: {boolean} Returns `true` if `value` is a {KeyObject}, `false` otherwise. ### `util.types.isMap(value)` <!-- YAML added: v10.0.0 --> * `value` {any} * Returns: {boolean} Returns `true` if the value is a built-in [`Map`][] instance. ```js util.types.isMap(new Map()); // Returns true ``` ### `util.types.isMapIterator(value)` <!-- YAML added: v10.0.0 --> * `value` {any} * Returns: {boolean} Returns `true` if the value is an iterator returned for a built-in [`Map`][] instance. ```js const map = new Map(); util.types.isMapIterator(map.keys()); // Returns true util.types.isMapIterator(map.values()); // Returns true util.types.isMapIterator(map.entries()); // Returns true util.types.isMapIterator(map[Symbol.iterator]()); // Returns true ``` ### `util.types.isModuleNamespaceObject(value)` <!-- YAML added: v10.0.0 --> * `value` {any} * Returns: {boolean} Returns `true` if the value is an instance of a [Module Namespace Object][]. ```mjs import * as ns from './a.js'; util.types.isModuleNamespaceObject(ns); // Returns true ``` ### `util.types.isNativeError(value)` <!-- YAML added: v10.0.0 --> * `value` {any} * Returns: {boolean} Returns `true` if the value was returned by the constructor of a [built-in `Error` type][]. ```js console.log(util.types.isNativeError(new Error())); // true console.log(util.types.isNativeError(new TypeError())); // true console.log(util.types.isNativeError(new RangeError())); // true ``` Subclasses of the native error types are also native errors: ```js class MyError extends Error {} console.log(util.types.isNativeError(new MyError())); // true ``` A value being `instanceof` a native error class is not equivalent to `isNativeError()` returning `true` for that value. `isNativeError()` returns `true` for errors which come from a different [realm][] while `instanceof Error` returns `false` for these errors: ```js const vm = require('node:vm'); const context = vm.createContext({}); const myError = vm.runInContext('new Error()', context); console.log(util.types.isNativeError(myError)); // true console.log(myError instanceof Error); // false ``` Conversely, `isNativeError()` returns `false` for all objects which were not returned by the constructor of a native error. That includes values which are `instanceof` native errors: ```js const myError = { __proto__: Error.prototype }; console.log(util.types.isNativeError(myError)); // false console.log(myError instanceof Error); // true ``` ### `util.types.isNumberObject(value)` <!-- YAML added: v10.0.0 --> * `value` {any} * Returns: {boolean} Returns `true` if the value is a number object, e.g. created by `new Number()`. ```js util.types.isNumberObject(0); // Returns false util.types.isNumberObject(new Number(0)); // Returns true ``` ### `util.types.isPromise(value)` <!-- YAML added: v10.0.0 --> * `value` {any} * Returns: {boolean} Returns `true` if the value is a built-in [`Promise`][]. ```js util.types.isPromise(Promise.resolve(42)); // Returns true ``` ### `util.types.isProxy(value)` <!-- YAML added: v10.0.0 --> * `value` {any} * Returns: {boolean} Returns `true` if the value is a [`Proxy`][] instance. ```js const target = {}; const proxy = new Proxy(target, {}); util.types.isProxy(target); // Returns false util.types.isProxy(proxy); // Returns true ``` ### `util.types.isRegExp(value)` <!-- YAML added: v10.0.0 --> * `value` {any} * Returns: {boolean} Returns `true` if the value is a regular expression object. ```js util.types.isRegExp(/abc/); // Returns true util.types.isRegExp(new RegExp('abc')); // Returns true ``` ### `util.types.isSet(value)` <!-- YAML added: v10.0.0 --> * `value` {any} * Returns: {boolean} Returns `true` if the value is a built-in [`Set`][] instance. ```js util.types.isSet(new Set()); // Returns true ``` ### `util.types.isSetIterator(value)` <!-- YAML added: v10.0.0 --> * `value` {any} * Returns: {boolean} Returns `true` if the value is an iterator returned for a built-in [`Set`][] instance. ```js const set = new Set(); util.types.isSetIterator(set.keys()); // Returns true util.types.isSetIterator(set.values()); // Returns true util.types.isSetIterator(set.entries()); // Returns true util.types.isSetIterator(set[Symbol.iterator]()); // Returns true ``` ### `util.types.isSharedArrayBuffer(value)` <!-- YAML added: v10.0.0 --> * `value` {any} * Returns: {boolean} Returns `true` if the value is a built-in [`SharedArrayBuffer`][] instance. This does _not_ include [`ArrayBuffer`][] instances. Usually, it is desirable to test for both; See [`util.types.isAnyArrayBuffer()`][] for that. ```js util.types.isSharedArrayBuffer(new ArrayBuffer()); // Returns false util.types.isSharedArrayBuffer(new SharedArrayBuffer()); // Returns true ``` ### `util.types.isStringObject(value)` <!-- YAML added: v10.0.0 --> * `value` {any} * Returns: {boolean} Returns `true` if the value is a string object, e.g. created by `new String()`. ```js util.types.isStringObject('foo'); // Returns false util.types.isStringObject(new String('foo')); // Returns true ``` ### `util.types.isSymbolObject(value)` <!-- YAML added: v10.0.0 --> * `value` {any} * Returns: {boolean} Returns `true` if the value is a symbol object, created by calling `Object()` on a `Symbol` primitive. ```js const symbol = Symbol('foo'); util.types.isSymbolObject(symbol); // Returns false util.types.isSymbolObject(Object(symbol)); // Returns true ``` ### `util.types.isTypedArray(value)` <!-- YAML added: v10.0.0 --> * `value` {any} * Returns: {boolean} Returns `true` if the value is a built-in [`TypedArray`][] instance. ```js util.types.isTypedArray(new ArrayBuffer()); // Returns false util.types.isTypedArray(new Uint8Array()); // Returns true util.types.isTypedArray(new Float64Array()); // Returns true ``` See also [`ArrayBuffer.isView()`][]. ### `util.types.isUint8Array(value)` <!-- YAML added: v10.0.0 --> * `value` {any} * Returns: {boolean} Returns `true` if the value is a built-in [`Uint8Array`][] instance. ```js util.types.isUint8Array(new ArrayBuffer()); // Returns false util.types.isUint8Array(new Uint8Array()); // Returns true util.types.isUint8Array(new Float64Array()); // Returns false ``` ### `util.types.isUint8ClampedArray(value)` <!-- YAML added: v10.0.0 --> * `value` {any} * Returns: {boolean} Returns `true` if the value is a built-in [`Uint8ClampedArray`][] instance. ```js util.types.isUint8ClampedArray(new ArrayBuffer()); // Returns false util.types.isUint8ClampedArray(new Uint8ClampedArray()); // Returns true util.types.isUint8ClampedArray(new Float64Array()); // Returns false ``` ### `util.types.isUint16Array(value)` <!-- YAML added: v10.0.0 --> * `value` {any} * Returns: {boolean} Returns `true` if the value is a built-in [`Uint16Array`][] instance. ```js util.types.isUint16Array(new ArrayBuffer()); // Returns false util.types.isUint16Array(new Uint16Array()); // Returns true util.types.isUint16Array(new Float64Array()); // Returns false ``` ### `util.types.isUint32Array(value)` <!-- YAML added: v10.0.0 --> * `value` {any} * Returns: {boolean} Returns `true` if the value is a built-in [`Uint32Array`][] instance. ```js util.types.isUint32Array(new ArrayBuffer()); // Returns false util.types.isUint32Array(new Uint32Array()); // Returns true util.types.isUint32Array(new Float64Array()); // Returns false ``` ### `util.types.isWeakMap(value)` <!-- YAML added: v10.0.0 --> * `value` {any} * Returns: {boolean} Returns `true` if the value is a built-in [`WeakMap`][] instance. ```js util.types.isWeakMap(new WeakMap()); // Returns true ``` ### `util.types.isWeakSet(value)` <!-- YAML added: v10.0.0 --> * `value` {any} * Returns: {boolean} Returns `true` if the value is a built-in [`WeakSet`][] instance. ```js util.types.isWeakSet(new WeakSet()); // Returns true ``` ## Deprecated APIs The following APIs are deprecated and should no longer be used. Existing applications and modules should be updated to find alternative approaches. ### `util._extend(target, source)` <!-- YAML added: v0.7.5 deprecated: v6.0.0 --> > Stability: 0 - Deprecated: Use [`Object.assign()`][] instead. * `target` {Object} * `source` {Object} The `util._extend()` method was never intended to be used outside of internal Node.js modules. The community found and used it anyway. It is deprecated and should not be used in new code. JavaScript comes with very similar built-in functionality through [`Object.assign()`][]. ### `util.isArray(object)` <!-- YAML added: v0.6.0 deprecated: v4.0.0 --> > Stability: 0 - Deprecated: Use [`Array.isArray()`][] instead. * `object` {any} * Returns: {boolean} Alias for [`Array.isArray()`][]. Returns `true` if the given `object` is an `Array`. Otherwise, returns `false`. ```js const util = require('node:util'); util.isArray([]); // Returns: true util.isArray(new Array()); // Returns: true util.isArray({}); // Returns: false ``` ### `util.isBoolean(object)` <!-- YAML added: v0.11.5 deprecated: v4.0.0 --> > Stability: 0 - Deprecated: Use `typeof value === 'boolean'` instead. * `object` {any} * Returns: {boolean} Returns `true` if the given `object` is a `Boolean`. Otherwise, returns `false`. ```js const util = require('node:util'); util.isBoolean(1); // Returns: false util.isBoolean(0); // Returns: false util.isBoolean(false); // Returns: true ``` ### `util.isBuffer(object)` <!-- YAML added: v0.11.5 deprecated: v4.0.0 --> > Stability: 0 - Deprecated: Use [`Buffer.isBuffer()`][] instead. * `object` {any} * Returns: {boolean} Returns `true` if the given `object` is a `Buffer`. Otherwise, returns `false`. ```js const util = require('node:util'); util.isBuffer({ length: 0 }); // Returns: false util.isBuffer([]); // Returns: false util.isBuffer(Buffer.from('hello world')); // Returns: true ``` ### `util.isDate(object)` <!-- YAML added: v0.6.0 deprecated: v4.0.0 --> > Stability: 0 - Deprecated: Use [`util.types.isDate()`][] instead. * `object` {any} * Returns: {boolean} Returns `true` if the given `object` is a `Date`. Otherwise, returns `false`. ```js const util = require('node:util'); util.isDate(new Date()); // Returns: true util.isDate(Date()); // false (without 'new' returns a String) util.isDate({}); // Returns: false ``` ### `util.isError(object)` <!-- YAML added: v0.6.0 deprecated: v4.0.0 --> > Stability: 0 - Deprecated: Use [`util.types.isNativeError()`][] instead. * `object` {any} * Returns: {boolean} Returns `true` if the given `object` is an [`Error`][]. Otherwise, returns `false`. ```js const util = require('node:util'); util.isError(new Error()); // Returns: true util.isError(new TypeError()); // Returns: true util.isError({ name: 'Error', message: 'an error occurred' }); // Returns: false ``` This method relies on `Object.prototype.toString()` behavior. It is possible to obtain an incorrect result when the `object` argument manipulates `@@toStringTag`. ```js const util = require('node:util'); const obj = { name: 'Error', message: 'an error occurred' }; util.isError(obj); // Returns: false obj[Symbol.toStringTag] = 'Error'; util.isError(obj); // Returns: true ``` ### `util.isFunction(object)` <!-- YAML added: v0.11.5 deprecated: v4.0.0 --> > Stability: 0 - Deprecated: Use `typeof value === 'function'` instead. * `object` {any} * Returns: {boolean} Returns `true` if the given `object` is a `Function`. Otherwise, returns `false`. ```js const util = require('node:util'); function Foo() {} const Bar = () => {}; util.isFunction({}); // Returns: false util.isFunction(Foo); // Returns: true util.isFunction(Bar); // Returns: true ``` ### `util.isNull(object)` <!-- YAML added: v0.11.5 deprecated: v4.0.0 --> > Stability: 0 - Deprecated: Use `value === null` instead. * `object` {any} * Returns: {boolean} Returns `true` if the given `object` is strictly `null`. Otherwise, returns `false`. ```js const util = require('node:util'); util.isNull(0); // Returns: false util.isNull(undefined); // Returns: false util.isNull(null); // Returns: true ``` ### `util.isNullOrUndefined(object)` <!-- YAML added: v0.11.5 deprecated: v4.0.0 --> > Stability: 0 - Deprecated: Use > `value === undefined || value === null` instead. * `object` {any} * Returns: {boolean} Returns `true` if the given `object` is `null` or `undefined`. Otherwise, returns `false`. ```js const util = require('node:util'); util.isNullOrUndefined(0); // Returns: false util.isNullOrUndefined(undefined); // Returns: true util.isNullOrUndefined(null); // Returns: true ``` ### `util.isNumber(object)` <!-- YAML added: v0.11.5 deprecated: v4.0.0 --> > Stability: 0 - Deprecated: Use `typeof value === 'number'` instead. * `object` {any} * Returns: {boolean} Returns `true` if the given `object` is a `Number`. Otherwise, returns `false`. ```js const util = require('node:util'); util.isNumber(false); // Returns: false util.isNumber(Infinity); // Returns: true util.isNumber(0); // Returns: true util.isNumber(NaN); // Returns: true ``` ### `util.isObject(object)` <!-- YAML added: v0.11.5 deprecated: v4.0.0 --> > Stability: 0 - Deprecated: > Use `value !== null && typeof value === 'object'` instead. * `object` {any} * Returns: {boolean} Returns `true` if the given `object` is strictly an `Object` **and** not a `Function` (even though functions are objects in JavaScript). Otherwise, returns `false`. ```js const util = require('node:util'); util.isObject(5); // Returns: false util.isObject(null); // Returns: false util.isObject({}); // Returns: true util.isObject(() => {}); // Returns: false ``` ### `util.isPrimitive(object)` <!-- YAML added: v0.11.5 deprecated: v4.0.0 --> > Stability: 0 - Deprecated: Use > `(typeof value !== 'object' && typeof value !== 'function') || value === null` > instead. * `object` {any} * Returns: {boolean} Returns `true` if the given `object` is a primitive type. Otherwise, returns `false`. ```js const util = require('node:util'); util.isPrimitive(5); // Returns: true util.isPrimitive('foo'); // Returns: true util.isPrimitive(false); // Returns: true util.isPrimitive(null); // Returns: true util.isPrimitive(undefined); // Returns: true util.isPrimitive({}); // Returns: false util.isPrimitive(() => {}); // Returns: false util.isPrimitive(/^$/); // Returns: false util.isPrimitive(new Date()); // Returns: false ``` ### `util.isRegExp(object)` <!-- YAML added: v0.6.0 deprecated: v4.0.0 --> > Stability: 0 - Deprecated * `object` {any} * Returns: {boolean} Returns `true` if the given `object` is a `RegExp`. Otherwise, returns `false`. ```js const util = require('node:util'); util.isRegExp(/some regexp/); // Returns: true util.isRegExp(new RegExp('another regexp')); // Returns: true util.isRegExp({}); // Returns: false ``` ### `util.isString(object)` <!-- YAML added: v0.11.5 deprecated: v4.0.0 --> > Stability: 0 - Deprecated: Use `typeof value === 'string'` instead. * `object` {any} * Returns: {boolean} Returns `true` if the given `object` is a `string`. Otherwise, returns `false`. ```js const util = require('node:util'); util.isString(''); // Returns: true util.isString('foo'); // Returns: true util.isString(String('foo')); // Returns: true util.isString(5); // Returns: false ``` ### `util.isSymbol(object)` <!-- YAML added: v0.11.5 deprecated: v4.0.0 --> > Stability: 0 - Deprecated: Use `typeof value === 'symbol'` instead. * `object` {any} * Returns: {boolean} Returns `true` if the given `object` is a `Symbol`. Otherwise, returns `false`. ```js const util = require('node:util'); util.isSymbol(5); // Returns: false util.isSymbol('foo'); // Returns: false util.isSymbol(Symbol('foo')); // Returns: true ``` ### `util.isUndefined(object)` <!-- YAML added: v0.11.5 deprecated: v4.0.0 --> > Stability: 0 - Deprecated: Use `value === undefined` instead. * `object` {any} * Returns: {boolean} Returns `true` if the given `object` is `undefined`. Otherwise, returns `false`. ```js const util = require('node:util'); const foo = undefined; util.isUndefined(5); // Returns: false util.isUndefined(foo); // Returns: true util.isUndefined(null); // Returns: false ``` ### `util.log(string)` <!-- YAML added: v0.3.0 deprecated: v6.0.0 --> > Stability: 0 - Deprecated: Use a third party module instead. * `string` {string} The `util.log()` method prints the given `string` to `stdout` with an included timestamp. ```js const util = require('node:util'); util.log('Timestamped message.'); ``` [Common System Errors]: errors.md#common-system-errors [Custom inspection functions on objects]: #custom-inspection-functions-on-objects [Custom promisified functions]: #custom-promisified-functions [Customizing `util.inspect` colors]: #customizing-utilinspect-colors [Internationalization]: intl.md [Module Namespace Object]: https://tc39.github.io/ecma262/#sec-module-namespace-exotic-objects [WHATWG Encoding Standard]: https://encoding.spec.whatwg.org/ [`'uncaughtException'`]: process.md#event-uncaughtexception [`'warning'`]: process.md#event-warning [`Array.isArray()`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/isArray [`ArrayBuffer.isView()`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer/isView [`ArrayBuffer`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer [`Buffer.isBuffer()`]: buffer.md#static-method-bufferisbufferobj [`DataView`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/DataView [`Date`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date [`Error`]: errors.md#class-error [`Float32Array`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Float32Array [`Float64Array`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Float64Array [`Int16Array`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Int16Array [`Int32Array`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Int32Array [`Int8Array`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Int8Array [`JSON.stringify()`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/JSON/stringify [`MIMEparams`]: #class-utilmimeparams [`Map`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Map [`Object.assign()`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/assign [`Object.freeze()`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/freeze [`Promise`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise [`Proxy`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Proxy [`Set`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set [`SharedArrayBuffer`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer [`TypedArray`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray [`Uint16Array`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint16Array [`Uint32Array`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint32Array [`Uint8Array`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array [`Uint8ClampedArray`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8ClampedArray [`WeakMap`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakMap [`WeakSet`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/WeakSet [`assert.deepStrictEqual()`]: assert.md#assertdeepstrictequalactual-expected-message [`console.error()`]: console.md#consoleerrordata-args [`mime.toString()`]: #mimetostring [`mimeParams.entries()`]: #mimeparamsentries [`napi_create_external()`]: n-api.md#napi_create_external [`target` and `handler`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Proxy#Terminology [`tty.hasColors()`]: tty.md#writestreamhascolorscount-env [`util.format()`]: #utilformatformat-args [`util.inspect()`]: #utilinspectobject-options [`util.promisify()`]: #utilpromisifyoriginal [`util.types.isAnyArrayBuffer()`]: #utiltypesisanyarraybuffervalue [`util.types.isArrayBuffer()`]: #utiltypesisarraybuffervalue [`util.types.isDate()`]: #utiltypesisdatevalue [`util.types.isNativeError()`]: #utiltypesisnativeerrorvalue [`util.types.isSharedArrayBuffer()`]: #utiltypesissharedarraybuffervalue [async function]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/async_function [built-in `Error` type]: https://tc39.es/ecma262/#sec-error-objects [compare function]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/sort#Parameters [constructor]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/constructor [default sort]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/sort [global symbol registry]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol/for [list of deprecated APIS]: deprecations.md#list-of-deprecated-apis [modifiers]: #modifiers [realm]: https://tc39.es/ecma262/#realm [semantically incompatible]: https://github.com/nodejs/node/issues/4179 [util.inspect.custom]: #utilinspectcustom