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<li><a href="#modules-nodemodule-api">Modules: <code>node:module</code> API</a>
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<li><a href="#the-module-object">The <code>Module</code> object</a>
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<li><a href="#modulebuiltinmodules"><code>module.builtinModules</code></a></li>
<li><a href="#modulecreaterequirefilename"><code>module.createRequire(filename)</code></a></li>
<li><span class="stability_1"><a href="#moduleconstantscompilecachestatus"><code>module.constants.compileCacheStatus</code></a></span></li>
<li><span class="stability_1"><a href="#moduleenablecompilecachecachedir"><code>module.enableCompileCache([cacheDir])</code></a></span>
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<li><a href="#module-compile-cache">Module compile cache</a></li>
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<li><span class="stability_1"><a href="#modulegetcompilecachedir"><code>module.getCompileCacheDir()</code></a></span></li>
<li><a href="#moduleisbuiltinmodulename"><code>module.isBuiltin(moduleName)</code></a></li>
<li><span class="stability_1"><a href="#moduleregisterspecifier-parenturl-options"><code>module.register(specifier[, parentURL][, options])</code></a></span></li>
<li><span class="stability_1"><a href="#modulestriptypescripttypescode-options"><code>module.stripTypeScriptTypes(code[, options])</code></a></span></li>
<li><a href="#modulesyncbuiltinesmexports"><code>module.syncBuiltinESMExports()</code></a></li>
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<li><a href="#module-compile-cache_1">Module compile cache</a>
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<li><span class="stability_1"><a href="#moduleconstantscompilecachestatus_1"><code>module.constants.compileCacheStatus</code></a></span></li>
<li><span class="stability_1"><a href="#moduleenablecompilecachecachedir_1"><code>module.enableCompileCache([cacheDir])</code></a></span></li>
<li><span class="stability_1"><a href="#moduleflushcompilecache"><code>module.flushCompileCache()</code></a></span></li>
<li><span class="stability_1"><a href="#modulegetcompilecachedir_1"><code>module.getCompileCacheDir()</code></a></span></li>
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<li><span class="stability_1"><a href="#customization-hooks">Customization Hooks</a></span>
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<li><a href="#enabling">Enabling</a></li>
<li><a href="#chaining">Chaining</a></li>
<li><a href="#communication-with-module-customization-hooks">Communication with module customization hooks</a></li>
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<li><span class="stability_1"><a href="#initialize"><code>initialize()</code></a></span></li>
<li><span class="stability_1"><a href="#resolvespecifier-context-nextresolve"><code>resolve(specifier, context, nextResolve)</code></a></span></li>
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<li><a href="https://nodejs.org/docs/latest-v13.x/api/module.html">13.x</a></li>
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<details role="navigation" id="toc" open><summary>Table of contents</summary><ul>
<li><a href="#modules-nodemodule-api">Modules: <code>node:module</code> API</a>
<ul>
<li><a href="#the-module-object">The <code>Module</code> object</a>
<ul>
<li><a href="#modulebuiltinmodules"><code>module.builtinModules</code></a></li>
<li><a href="#modulecreaterequirefilename"><code>module.createRequire(filename)</code></a></li>
<li><span class="stability_1"><a href="#moduleconstantscompilecachestatus"><code>module.constants.compileCacheStatus</code></a></span></li>
<li><span class="stability_1"><a href="#moduleenablecompilecachecachedir"><code>module.enableCompileCache([cacheDir])</code></a></span>
<ul>
<li><a href="#module-compile-cache">Module compile cache</a></li>
</ul>
</li>
<li><span class="stability_1"><a href="#modulegetcompilecachedir"><code>module.getCompileCacheDir()</code></a></span></li>
<li><a href="#moduleisbuiltinmodulename"><code>module.isBuiltin(moduleName)</code></a></li>
<li><span class="stability_1"><a href="#moduleregisterspecifier-parenturl-options"><code>module.register(specifier[, parentURL][, options])</code></a></span></li>
<li><span class="stability_1"><a href="#modulestriptypescripttypescode-options"><code>module.stripTypeScriptTypes(code[, options])</code></a></span></li>
<li><a href="#modulesyncbuiltinesmexports"><code>module.syncBuiltinESMExports()</code></a></li>
</ul>
</li>
<li><a href="#module-compile-cache_1">Module compile cache</a>
<ul>
<li><span class="stability_1"><a href="#moduleconstantscompilecachestatus_1"><code>module.constants.compileCacheStatus</code></a></span></li>
<li><span class="stability_1"><a href="#moduleenablecompilecachecachedir_1"><code>module.enableCompileCache([cacheDir])</code></a></span></li>
<li><span class="stability_1"><a href="#moduleflushcompilecache"><code>module.flushCompileCache()</code></a></span></li>
<li><span class="stability_1"><a href="#modulegetcompilecachedir_1"><code>module.getCompileCacheDir()</code></a></span></li>
</ul>
</li>
<li><span class="stability_1"><a href="#customization-hooks">Customization Hooks</a></span>
<ul>
<li><a href="#enabling">Enabling</a></li>
<li><a href="#chaining">Chaining</a></li>
<li><a href="#communication-with-module-customization-hooks">Communication with module customization hooks</a></li>
<li><a href="#hooks">Hooks</a>
<ul>
<li><span class="stability_1"><a href="#initialize"><code>initialize()</code></a></span></li>
<li><span class="stability_1"><a href="#resolvespecifier-context-nextresolve"><code>resolve(specifier, context, nextResolve)</code></a></span></li>
<li><span class="stability_1"><a href="#loadurl-context-nextload"><code>load(url, context, nextLoad)</code></a></span></li>
</ul>
</li>
<li><a href="#examples">Examples</a>
<ul>
<li><a href="#import-from-https">Import from HTTPS</a></li>
<li><a href="#transpilation">Transpilation</a></li>
<li><a href="#import-maps">Import maps</a></li>
</ul>
</li>
</ul>
</li>
<li><span class="stability_1"><a href="#source-map-v3-support">Source map v3 support</a></span>
<ul>
<li><a href="#modulefindsourcemappath"><code>module.findSourceMap(path)</code></a></li>
<li><a href="#class-modulesourcemap">Class: <code>module.SourceMap</code></a>
<ul>
<li><a href="#new-sourcemappayload--linelengths-"><code>new SourceMap(payload[, { lineLengths }])</code></a></li>
<li><a href="#sourcemappayload"><code>sourceMap.payload</code></a></li>
<li><a href="#sourcemapfindentrylineoffset-columnoffset"><code>sourceMap.findEntry(lineOffset, columnOffset)</code></a></li>
<li><a href="#sourcemapfindoriginlinenumber-columnnumber"><code>sourceMap.findOrigin(lineNumber, columnNumber)</code></a></li>
</ul>
</li>
</ul>
</li>
</ul>
</li>
</ul></details>
<div role="main" id="apicontent">
<h2>Modules: <code>node:module</code> API<span><a class="mark" href="#modules-nodemodule-api" id="modules-nodemodule-api">#</a></span><a aria-hidden="true" class="legacy" id="module_modules_node_module_api"></a></h2>
<div class="api_metadata">
<span>Added in: v0.3.7</span>
</div>
<section><h3>The <code>Module</code> object<span><a class="mark" href="#the-module-object" id="the-module-object">#</a></span><a aria-hidden="true" class="legacy" id="module_the_module_object"></a></h3>
<ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li>
</ul>
<p>Provides general utility methods when interacting with instances of
<code>Module</code>, the <a href="#the-module-object"><code>module</code></a> variable often seen in <a href="modules.html">CommonJS</a> modules. Accessed
via <code>import 'node:module'</code> or <code>require('node:module')</code>.</p>
<h4><code>module.builtinModules</code><span><a class="mark" href="#modulebuiltinmodules" id="modulebuiltinmodules">#</a></span><a aria-hidden="true" class="legacy" id="module_module_builtinmodules"></a></h4>
<div class="api_metadata">
<span>Added in: v9.3.0, v8.10.0, v6.13.0</span>
</div>
<ul>
<li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string[]></a></li>
</ul>
<p>A list of the names of all modules provided by Node.js. Can be used to verify
if a module is maintained by a third party or not.</p>
<p>Note: the list doesn't contain <a href="modules.html#built-in-modules-with-mandatory-node-prefix">prefix-only modules</a> like <code>node:test</code>.</p>
<p><code>module</code> in this context isn't the same object that's provided
by the <a href="modules.html#the-module-wrapper">module wrapper</a>. To access it, require the <code>Module</code> module:</p>
<pre class="with-26-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-comment">// module.mjs</span>
<span class="hljs-comment">// In an ECMAScript module</span>
<span class="hljs-keyword">import</span> { builtinModules <span class="hljs-keyword">as</span> builtin } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:module'</span>;</code><code class="language-js cjs"><span class="hljs-comment">// module.cjs</span>
<span class="hljs-comment">// In a CommonJS module</span>
<span class="hljs-keyword">const</span> builtin = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:module'</span>).<span class="hljs-property">builtinModules</span>;</code><button class="copy-button">copy</button></pre>
<h4><code>module.createRequire(filename)</code><span><a class="mark" href="#modulecreaterequirefilename" id="modulecreaterequirefilename">#</a></span><a aria-hidden="true" class="legacy" id="module_module_createrequire_filename"></a></h4>
<div class="api_metadata">
<span>Added in: v12.2.0</span>
</div>
<ul>
<li><code>filename</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="url.html#the-whatwg-url-api" class="type"><URL></a> Filename to be used to construct the require
function. Must be a file URL object, file URL string, or absolute path
string.</li>
<li>Returns: <a href="modules.html#requireid" class="type"><require></a> Require function</li>
</ul>
<pre><code class="language-js mjs"><span class="hljs-keyword">import</span> { createRequire } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:module'</span>;
<span class="hljs-keyword">const</span> <span class="hljs-built_in">require</span> = <span class="hljs-title function_">createRequire</span>(<span class="hljs-keyword">import</span>.<span class="hljs-property">meta</span>.<span class="hljs-property">url</span>);
<span class="hljs-comment">// sibling-module.js is a CommonJS module.</span>
<span class="hljs-keyword">const</span> siblingModule = <span class="hljs-built_in">require</span>(<span class="hljs-string">'./sibling-module'</span>);</code> <button class="copy-button">copy</button></pre>
<h4><code>module.constants.compileCacheStatus</code><span><a class="mark" href="#moduleconstantscompilecachestatus" id="moduleconstantscompilecachestatus">#</a></span><a aria-hidden="true" class="legacy" id="module_module_constants_compilecachestatus"></a></h4>
<div class="api_metadata">
<span>Added in: v22.8.0</span>
</div>
<p></p><div class="api_stability api_stability_1"><a href="documentation.html#stability-index">Stability: 1</a>.1 - Active Development</div><p></p>
<p>The following constants are returned as the <code>status</code> field in the object returned by
<a href="#moduleenablecompilecachecachedir"><code>module.enableCompileCache()</code></a> to indicate the result of the attempt to enable the
<a href="#module-compile-cache">module compile cache</a>.</p>
<table>
<tbody><tr>
<th>Constant</th>
<th>Description</th>
</tr>
<tr>
<td><code>ENABLED</code></td>
<td>
Node.js has enabled the compile cache successfully. The directory used to store the
compile cache will be returned in the <code>directory</code> field in the
returned object.
</td>
</tr>
<tr>
<td><code>ALREADY_ENABLED</code></td>
<td>
The compile cache has already been enabled before, either by a previous call to
<code>module.enableCompileCache()</code>, or by the <code>NODE_COMPILE_CACHE=dir</code>
environment variable. The directory used to store the
compile cache will be returned in the <code>directory</code> field in the
returned object.
</td>
</tr>
<tr>
<td><code>FAILED</code></td>
<td>
Node.js fails to enable the compile cache. This can be caused by the lack of
permission to use the specified directory, or various kinds of file system errors.
The detail of the failure will be returned in the <code>message</code> field in the
returned object.
</td>
</tr>
<tr>
<td><code>DISABLED</code></td>
<td>
Node.js cannot enable the compile cache because the environment variable
<code>NODE_DISABLE_COMPILE_CACHE=1</code> has been set.
</td>
</tr>
</tbody></table>
<h4><code>module.enableCompileCache([cacheDir])</code><span><a class="mark" href="#moduleenablecompilecachecachedir" id="moduleenablecompilecachecachedir">#</a></span><a aria-hidden="true" class="legacy" id="module_module_enablecompilecache_cachedir"></a></h4>
<div class="api_metadata">
<span>Added in: v22.8.0</span>
</div>
<p></p><div class="api_stability api_stability_1"><a href="documentation.html#stability-index">Stability: 1</a>.1 - Active Development</div><p></p>
<ul>
<li><code>cacheDir</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type"><undefined></a> Optional path to specify the directory where the compile cache
will be stored/retrieved.</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a>
<ul>
<li><code>status</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><integer></a> One of the <a href="#moduleconstantscompilecachestatus"><code>module.constants.compileCacheStatus</code></a></li>
<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type"><undefined></a> If Node.js cannot enable the compile cache, this contains
the error message. Only set if <code>status</code> is <code>module.constants.compileCacheStatus.FAILED</code>.</li>
<li><code>directory</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type"><undefined></a> If the compile cache is enabled, this contains the directory
where the compile cache is stored. Only set if <code>status</code> is
<code>module.constants.compileCacheStatus.ENABLED</code> or
<code>module.constants.compileCacheStatus.ALREADY_ENABLED</code>.</li>
</ul>
</li>
</ul>
<p>Enable <a href="#module-compile-cache">module compile cache</a> in the current Node.js instance.</p>
<p>If <code>cacheDir</code> is not specified, Node.js will either use the directory specified by the
<a href="cli.html#node_compile_cachedir"><code>NODE_COMPILE_CACHE=dir</code></a> environment variable if it's set, or use
<code>path.join(os.tmpdir(), 'node-compile-cache')</code> otherwise. For general use cases, it's
recommended to call <code>module.enableCompileCache()</code> without specifying the <code>cacheDir</code>,
so that the directory can be overriden by the <code>NODE_COMPILE_CACHE</code> environment
variable when necessary.</p>
<p>Since compile cache is supposed to be a quiet optimization that is not required for the
application to be functional, this method is designed to not throw any exception when the
compile cache cannot be enabled. Instead, it will return an object containing an error
message in the <code>message</code> field to aid debugging.
If compile cache is enabled successefully, the <code>directory</code> field in the returned object
contains the path to the directory where the compile cache is stored. The <code>status</code>
field in the returned object would be one of the <code>module.constants.compileCacheStatus</code>
values to indicate the result of the attempt to enable the <a href="#module-compile-cache">module compile cache</a>.</p>
<p>This method only affects the current Node.js instance. To enable it in child worker threads,
either call this method in child worker threads too, or set the
<code>process.env.NODE_COMPILE_CACHE</code> value to compile cache directory so the behavior can
be inheritend into the child workers. The directory can be obtained either from the
<code>directory</code> field returned by this method, or with <a href="#modulegetcompilecachedir"><code>module.getCompileCacheDir()</code></a>.</p>
<h5>Module compile cache<span><a class="mark" href="#module-compile-cache" id="module-compile-cache">#</a></span><a aria-hidden="true" class="legacy" id="module_module_compile_cache"></a></h5>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v22.8.0</td>
<td><p>add initial JavaScript APIs for runtime access.</p></td></tr>
<tr><td>v22.1.0</td>
<td><p><span>Added in: v22.1.0</span></p></td></tr>
</tbody></table>
</details>
</div>
<p>The module compile cache can be enabled either using the <a href="#moduleenablecompilecachecachedir"><code>module.enableCompileCache()</code></a>
method or the <a href="cli.html#node_compile_cachedir"><code>NODE_COMPILE_CACHE=dir</code></a> environment variable. After it is enabled,
whenever Node.js compiles a CommonJS or a ECMAScript Module, it will use on-disk
<a href="https://v8.dev/blog/code-caching-for-devs">V8 code cache</a> persisted in the specified directory to speed up the compilation.
This may slow down the first load of a module graph, but subsequent loads of the same module
graph may get a significant speedup if the contents of the modules do not change.</p>
<p>To clean up the generated compile cache on disk, simply remove the cache directory. The cache
directory will be recreated the next time the same directory is used for for compile cache
storage. To avoid filling up the disk with stale cache, it is recommended to use a directory
under the <a href="os.html#ostmpdir"><code>os.tmpdir()</code></a>. If the compile cache is enabled by a call to
<a href="#moduleenablecompilecachecachedir"><code>module.enableCompileCache()</code></a> without specifying the directory, Node.js will use
the <a href="cli.html#node_compile_cachedir"><code>NODE_COMPILE_CACHE=dir</code></a> environment variable if it's set, or defaults
to <code>path.join(os.tmpdir(), 'node-compile-cache')</code> otherwise. To locate the compile cache
directory used by a running Node.js instance, use <a href="#modulegetcompilecachedir"><code>module.getCompileCacheDir()</code></a>.</p>
<p>Currently when using the compile cache with <a href="https://v8project.blogspot.com/2017/12/javascript-code-coverage.html">V8 JavaScript code coverage</a>, the
coverage being collected by V8 may be less precise in functions that are
deserialized from the code cache. It's recommended to turn this off when
running tests to generate precise coverage.</p>
<p>The enabled module compile cache can be disabled by the <a href="cli.html#node_disable_compile_cache1"><code>NODE_DISABLE_COMPILE_CACHE=1</code></a>
environment variable. This can be useful when the compile cache leads to unexpected or
undesired behaviors (e.g. less precise test coverage).</p>
<p>Compilation cache generated by one version of Node.js can not be reused by a different
version of Node.js. Cache generated by different versions of Node.js will be stored
separately if the same base directory is used to persist the cache, so they can co-exist.</p>
<p>At the moment, when the compile cache is enabled and a module is loaded afresh, the
code cache is generated from the compiled code immediately, but will only be written
to disk when the Node.js instance is about to exit. This is subject to change. The
<a href="#moduleflushcompilecache"><code>module.flushCompileCache()</code></a> method can be used to ensure the accumulated code cache
is flushed to disk in case the application wants to spawn other Node.js instances
and let them share the cache long before the parent exits.</p>
<h4><code>module.getCompileCacheDir()</code><span><a class="mark" href="#modulegetcompilecachedir" id="modulegetcompilecachedir">#</a></span><a aria-hidden="true" class="legacy" id="module_module_getcompilecachedir"></a></h4>
<div class="api_metadata">
<span>Added in: v22.8.0</span>
</div>
<p></p><div class="api_stability api_stability_1"><a href="documentation.html#stability-index">Stability: 1</a>.1 - Active Development</div><p></p>
<ul>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type"><undefined></a> Path to the <a href="#module-compile-cache">module compile cache</a> directory if it is enabled,
or <code>undefined</code> otherwise.</li>
</ul>
<h4><code>module.isBuiltin(moduleName)</code><span><a class="mark" href="#moduleisbuiltinmodulename" id="moduleisbuiltinmodulename">#</a></span><a aria-hidden="true" class="legacy" id="module_module_isbuiltin_modulename"></a></h4>
<div class="api_metadata">
<span>Added in: v18.6.0, v16.17.0</span>
</div>
<ul>
<li><code>moduleName</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> name of the module</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> returns true if the module is builtin else returns false</li>
</ul>
<pre><code class="language-js mjs"><span class="hljs-keyword">import</span> { isBuiltin } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:module'</span>;
<span class="hljs-title function_">isBuiltin</span>(<span class="hljs-string">'node:fs'</span>); <span class="hljs-comment">// true</span>
<span class="hljs-title function_">isBuiltin</span>(<span class="hljs-string">'fs'</span>); <span class="hljs-comment">// true</span>
<span class="hljs-title function_">isBuiltin</span>(<span class="hljs-string">'wss'</span>); <span class="hljs-comment">// false</span></code> <button class="copy-button">copy</button></pre>
<h4><code>module.register(specifier[, parentURL][, options])</code><span><a class="mark" href="#moduleregisterspecifier-parenturl-options" id="moduleregisterspecifier-parenturl-options">#</a></span><a aria-hidden="true" class="legacy" id="module_module_register_specifier_parenturl_options"></a></h4>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v20.8.0, v18.19.0</td>
<td><p>Add support for WHATWG URL instances.</p></td></tr>
<tr><td>v20.6.0, v18.19.0</td>
<td><p><span>Added in: v20.6.0, v18.19.0</span></p></td></tr>
</tbody></table>
</details>
</div>
<p></p><div class="api_stability api_stability_1"><a href="documentation.html#stability-index">Stability: 1</a>.2 - Release candidate</div><p></p>
<ul>
<li><code>specifier</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="url.html#the-whatwg-url-api" class="type"><URL></a> Customization hooks to be registered; this should be
the same string that would be passed to <code>import()</code>, except that if it is
relative, it is resolved relative to <code>parentURL</code>.</li>
<li><code>parentURL</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="url.html#the-whatwg-url-api" class="type"><URL></a> If you want to resolve <code>specifier</code> relative to a base
URL, such as <code>import.meta.url</code>, you can pass that URL here. <strong>Default:</strong>
<code>'data:'</code></li>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a>
<ul>
<li><code>parentURL</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="url.html#the-whatwg-url-api" class="type"><URL></a> If you want to resolve <code>specifier</code> relative to a
base URL, such as <code>import.meta.url</code>, you can pass that URL here. This
property is ignored if the <code>parentURL</code> is supplied as the second argument.
<strong>Default:</strong> <code>'data:'</code></li>
<li><code>data</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a> Any arbitrary, cloneable JavaScript value to pass into the
<a href="#initialize"><code>initialize</code></a> hook.</li>
<li><code>transferList</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object[]></a> <a href="worker_threads.html#portpostmessagevalue-transferlist">transferrable objects</a> to be passed into the
<code>initialize</code> hook.</li>
</ul>
</li>
</ul>
<p>Register a module that exports <a href="#customization-hooks">hooks</a> that customize Node.js module
resolution and loading behavior. See <a href="#customization-hooks">Customization hooks</a>.</p>
<h4><code>module.stripTypeScriptTypes(code[, options])</code><span><a class="mark" href="#modulestriptypescripttypescode-options" id="modulestriptypescripttypescode-options">#</a></span><a aria-hidden="true" class="legacy" id="module_module_striptypescripttypes_code_options"></a></h4>
<div class="api_metadata">
<span>Added in: v22.13.0</span>
</div>
<p></p><div class="api_stability api_stability_1"><a href="documentation.html#stability-index">Stability: 1</a>.1 - Active development</div><p></p>
<ul>
<li><code>code</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> The code to strip type annotations from.</li>
<li><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a>
<ul>
<li><code>mode</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> <strong>Default:</strong> <code>'strip'</code>. Possible values are:
<ul>
<li><code>'strip'</code> Only strip type annotations without performing the transformation of TypeScript features.</li>
<li><code>'transform'</code> Strip type annotations and transform TypeScript features to JavaScript.</li>
</ul>
</li>
<li><code>sourceMap</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> <strong>Default:</strong> <code>false</code>. Only when <code>mode</code> is <code>'transform'</code>, if <code>true</code>, a source map
will be generated for the transformed code.</li>
<li><code>sourceUrl</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> Specifies the source url used in the source map.</li>
</ul>
</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> The code with type annotations stripped.
<code>module.stripTypeScriptTypes()</code> removes type annotations from TypeScript code. It
can be used to strip type annotations from TypeScript code before running it
with <code>vm.runInContext()</code> or <code>vm.compileFunction()</code>.
By default, it will throw an error if the code contains TypeScript features
that require transformation such as <code>Enums</code>,
see <a href="typescript.html#type-stripping">type-stripping</a> for more information.
When mode is <code>'transform'</code>, it also transforms TypeScript features to JavaScript,
see <a href="typescript.html#typescript-features">transform TypeScript features</a> for more information.
When mode is <code>'strip'</code>, source maps are not generated, because locations are preserved.
If <code>sourceMap</code> is provided, when mode is <code>'strip'</code>, an error will be thrown.</li>
</ul>
<p><em>WARNING</em>: The output of this function should not be considered stable across Node.js versions,
due to changes in the TypeScript parser.</p>
<pre class="with-56-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> { stripTypeScriptTypes } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:module'</span>;
<span class="hljs-keyword">const</span> code = <span class="hljs-string">'const a: number = 1;'</span>;
<span class="hljs-keyword">const</span> strippedCode = <span class="hljs-title function_">stripTypeScriptTypes</span>(code);
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(strippedCode);
<span class="hljs-comment">// Prints: const a = 1;</span></code><code class="language-js cjs"><span class="hljs-keyword">const</span> { stripTypeScriptTypes } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:module'</span>);
<span class="hljs-keyword">const</span> code = <span class="hljs-string">'const a: number = 1;'</span>;
<span class="hljs-keyword">const</span> strippedCode = <span class="hljs-title function_">stripTypeScriptTypes</span>(code);
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(strippedCode);
<span class="hljs-comment">// Prints: const a = 1;</span></code><button class="copy-button">copy</button></pre>
<p>If <code>sourceUrl</code> is provided, it will be used appended as a comment at the end of the output:</p>
<pre class="with-56-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> { stripTypeScriptTypes } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:module'</span>;
<span class="hljs-keyword">const</span> code = <span class="hljs-string">'const a: number = 1;'</span>;
<span class="hljs-keyword">const</span> strippedCode = <span class="hljs-title function_">stripTypeScriptTypes</span>(code, { <span class="hljs-attr">mode</span>: <span class="hljs-string">'strip'</span>, <span class="hljs-attr">sourceUrl</span>: <span class="hljs-string">'source.ts'</span> });
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(strippedCode);
<span class="hljs-comment">// Prints: const a = 1\n\n//# sourceURL=source.ts;</span></code><code class="language-js cjs"><span class="hljs-keyword">const</span> { stripTypeScriptTypes } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:module'</span>);
<span class="hljs-keyword">const</span> code = <span class="hljs-string">'const a: number = 1;'</span>;
<span class="hljs-keyword">const</span> strippedCode = <span class="hljs-title function_">stripTypeScriptTypes</span>(code, { <span class="hljs-attr">mode</span>: <span class="hljs-string">'strip'</span>, <span class="hljs-attr">sourceUrl</span>: <span class="hljs-string">'source.ts'</span> });
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(strippedCode);
<span class="hljs-comment">// Prints: const a = 1\n\n//# sourceURL=source.ts;</span></code><button class="copy-button">copy</button></pre>
<p>When <code>mode</code> is <code>'transform'</code>, the code is transformed to JavaScript:</p>
<pre class="with-56-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> { stripTypeScriptTypes } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:module'</span>;
<span class="hljs-keyword">const</span> code = <span class="hljs-string">`
namespace MathUtil {
export const add = (a: number, b: number) => a + b;
}`</span>;
<span class="hljs-keyword">const</span> strippedCode = <span class="hljs-title function_">stripTypeScriptTypes</span>(code, { <span class="hljs-attr">mode</span>: <span class="hljs-string">'transform'</span>, <span class="hljs-attr">sourceMap</span>: <span class="hljs-literal">true</span> });
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(strippedCode);
<span class="hljs-comment">// Prints:</span>
<span class="hljs-comment">// var MathUtil;</span>
<span class="hljs-comment">// (function(MathUtil) {</span>
<span class="hljs-comment">// MathUtil.add = (a, b)=>a + b;</span>
<span class="hljs-comment">// })(MathUtil || (MathUtil = {}));</span>
<span class="hljs-comment">// # sourceMappingURL=data:application/json;base64, ...</span></code><code class="language-js cjs"><span class="hljs-keyword">const</span> { stripTypeScriptTypes } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:module'</span>);
<span class="hljs-keyword">const</span> code = <span class="hljs-string">`
namespace MathUtil {
export const add = (a: number, b: number) => a + b;
}`</span>;
<span class="hljs-keyword">const</span> strippedCode = <span class="hljs-title function_">stripTypeScriptTypes</span>(code, { <span class="hljs-attr">mode</span>: <span class="hljs-string">'transform'</span>, <span class="hljs-attr">sourceMap</span>: <span class="hljs-literal">true</span> });
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(strippedCode);
<span class="hljs-comment">// Prints:</span>
<span class="hljs-comment">// var MathUtil;</span>
<span class="hljs-comment">// (function(MathUtil) {</span>
<span class="hljs-comment">// MathUtil.add = (a, b)=>a + b;</span>
<span class="hljs-comment">// })(MathUtil || (MathUtil = {}));</span>
<span class="hljs-comment">// # sourceMappingURL=data:application/json;base64, ...</span></code><button class="copy-button">copy</button></pre>
<h4><code>module.syncBuiltinESMExports()</code><span><a class="mark" href="#modulesyncbuiltinesmexports" id="modulesyncbuiltinesmexports">#</a></span><a aria-hidden="true" class="legacy" id="module_module_syncbuiltinesmexports"></a></h4>
<div class="api_metadata">
<span>Added in: v12.12.0</span>
</div>
<p>The <code>module.syncBuiltinESMExports()</code> method updates all the live bindings for
builtin <a href="esm.html">ES Modules</a> to match the properties of the <a href="modules.html">CommonJS</a> exports. It
does not add or remove exported names from the <a href="esm.html">ES Modules</a>.</p>
<pre><code class="language-js"><span class="hljs-keyword">const</span> fs = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:fs'</span>);
<span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert'</span>);
<span class="hljs-keyword">const</span> { syncBuiltinESMExports } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:module'</span>);
fs.<span class="hljs-property">readFile</span> = newAPI;
<span class="hljs-keyword">delete</span> fs.<span class="hljs-property">readFileSync</span>;
<span class="hljs-keyword">function</span> <span class="hljs-title function_">newAPI</span>(<span class="hljs-params"></span>) {
<span class="hljs-comment">// ...</span>
}
fs.<span class="hljs-property">newAPI</span> = newAPI;
<span class="hljs-title function_">syncBuiltinESMExports</span>();
<span class="hljs-keyword">import</span>(<span class="hljs-string">'node:fs'</span>).<span class="hljs-title function_">then</span>(<span class="hljs-function">(<span class="hljs-params">esmFS</span>) =></span> {
<span class="hljs-comment">// It syncs the existing readFile property with the new value</span>
assert.<span class="hljs-title function_">strictEqual</span>(esmFS.<span class="hljs-property">readFile</span>, newAPI);
<span class="hljs-comment">// readFileSync has been deleted from the required fs</span>
assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-string">'readFileSync'</span> <span class="hljs-keyword">in</span> fs, <span class="hljs-literal">false</span>);
<span class="hljs-comment">// syncBuiltinESMExports() does not remove readFileSync from esmFS</span>
assert.<span class="hljs-title function_">strictEqual</span>(<span class="hljs-string">'readFileSync'</span> <span class="hljs-keyword">in</span> esmFS, <span class="hljs-literal">true</span>);
<span class="hljs-comment">// syncBuiltinESMExports() does not add names</span>
assert.<span class="hljs-title function_">strictEqual</span>(esmFS.<span class="hljs-property">newAPI</span>, <span class="hljs-literal">undefined</span>);
});</code> <button class="copy-button">copy</button></pre>
</section><section><h3>Module compile cache<span><a class="mark" href="#module-compile-cache_1" id="module-compile-cache_1">#</a></span><a aria-hidden="true" class="legacy" id="module_module_compile_cache_1"></a></h3>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v22.8.0</td>
<td><p>add initial JavaScript APIs for runtime access.</p></td></tr>
<tr><td>v22.1.0</td>
<td><p><span>Added in: v22.1.0</span></p></td></tr>
</tbody></table>
</details>
</div>
<p>The module compile cache can be enabled either using the <a href="#moduleenablecompilecachecachedir"><code>module.enableCompileCache()</code></a>
method or the <a href="cli.html#node_compile_cachedir"><code>NODE_COMPILE_CACHE=dir</code></a> environment variable. After it is enabled,
whenever Node.js compiles a CommonJS or a ECMAScript Module, it will use on-disk
<a href="https://v8.dev/blog/code-caching-for-devs">V8 code cache</a> persisted in the specified directory to speed up the compilation.
This may slow down the first load of a module graph, but subsequent loads of the same module
graph may get a significant speedup if the contents of the modules do not change.</p>
<p>To clean up the generated compile cache on disk, simply remove the cache directory. The cache
directory will be recreated the next time the same directory is used for for compile cache
storage. To avoid filling up the disk with stale cache, it is recommended to use a directory
under the <a href="os.html#ostmpdir"><code>os.tmpdir()</code></a>. If the compile cache is enabled by a call to
<a href="#moduleenablecompilecachecachedir"><code>module.enableCompileCache()</code></a> without specifying the directory, Node.js will use
the <a href="cli.html#node_compile_cachedir"><code>NODE_COMPILE_CACHE=dir</code></a> environment variable if it's set, or defaults
to <code>path.join(os.tmpdir(), 'node-compile-cache')</code> otherwise. To locate the compile cache
directory used by a running Node.js instance, use <a href="#modulegetcompilecachedir"><code>module.getCompileCacheDir()</code></a>.</p>
<p>Currently when using the compile cache with <a href="https://v8project.blogspot.com/2017/12/javascript-code-coverage.html">V8 JavaScript code coverage</a>, the
coverage being collected by V8 may be less precise in functions that are
deserialized from the code cache. It's recommended to turn this off when
running tests to generate precise coverage.</p>
<p>The enabled module compile cache can be disabled by the <a href="cli.html#node_disable_compile_cache1"><code>NODE_DISABLE_COMPILE_CACHE=1</code></a>
environment variable. This can be useful when the compile cache leads to unexpected or
undesired behaviors (e.g. less precise test coverage).</p>
<p>Compilation cache generated by one version of Node.js can not be reused by a different
version of Node.js. Cache generated by different versions of Node.js will be stored
separately if the same base directory is used to persist the cache, so they can co-exist.</p>
<p>At the moment, when the compile cache is enabled and a module is loaded afresh, the
code cache is generated from the compiled code immediately, but will only be written
to disk when the Node.js instance is about to exit. This is subject to change. The
<a href="#moduleflushcompilecache"><code>module.flushCompileCache()</code></a> method can be used to ensure the accumulated code cache
is flushed to disk in case the application wants to spawn other Node.js instances
and let them share the cache long before the parent exits.</p>
<h4><code>module.constants.compileCacheStatus</code><span><a class="mark" href="#moduleconstantscompilecachestatus_1" id="moduleconstantscompilecachestatus_1">#</a></span><a aria-hidden="true" class="legacy" id="module_module_constants_compilecachestatus_1"></a></h4>
<div class="api_metadata">
<span>Added in: v22.8.0</span>
</div>
<p></p><div class="api_stability api_stability_1"><a href="documentation.html#stability-index">Stability: 1</a>.1 - Active Development</div><p></p>
<p>The following constants are returned as the <code>status</code> field in the object returned by
<a href="#moduleenablecompilecachecachedir"><code>module.enableCompileCache()</code></a> to indicate the result of the attempt to enable the
<a href="#module-compile-cache">module compile cache</a>.</p>
<table>
<tbody><tr>
<th>Constant</th>
<th>Description</th>
</tr>
<tr>
<td><code>ENABLED</code></td>
<td>
Node.js has enabled the compile cache successfully. The directory used to store the
compile cache will be returned in the <code>directory</code> field in the
returned object.
</td>
</tr>
<tr>
<td><code>ALREADY_ENABLED</code></td>
<td>
The compile cache has already been enabled before, either by a previous call to
<code>module.enableCompileCache()</code>, or by the <code>NODE_COMPILE_CACHE=dir</code>
environment variable. The directory used to store the
compile cache will be returned in the <code>directory</code> field in the
returned object.
</td>
</tr>
<tr>
<td><code>FAILED</code></td>
<td>
Node.js fails to enable the compile cache. This can be caused by the lack of
permission to use the specified directory, or various kinds of file system errors.
The detail of the failure will be returned in the <code>message</code> field in the
returned object.
</td>
</tr>
<tr>
<td><code>DISABLED</code></td>
<td>
Node.js cannot enable the compile cache because the environment variable
<code>NODE_DISABLE_COMPILE_CACHE=1</code> has been set.
</td>
</tr>
</tbody></table>
<h4><code>module.enableCompileCache([cacheDir])</code><span><a class="mark" href="#moduleenablecompilecachecachedir_1" id="moduleenablecompilecachecachedir_1">#</a></span><a aria-hidden="true" class="legacy" id="module_module_enablecompilecache_cachedir_1"></a></h4>
<div class="api_metadata">
<span>Added in: v22.8.0</span>
</div>
<p></p><div class="api_stability api_stability_1"><a href="documentation.html#stability-index">Stability: 1</a>.1 - Active Development</div><p></p>
<ul>
<li><code>cacheDir</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type"><undefined></a> Optional path to specify the directory where the compile cache
will be stored/retrieved.</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a>
<ul>
<li><code>status</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><integer></a> One of the <a href="#moduleconstantscompilecachestatus"><code>module.constants.compileCacheStatus</code></a></li>
<li><code>message</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type"><undefined></a> If Node.js cannot enable the compile cache, this contains
the error message. Only set if <code>status</code> is <code>module.constants.compileCacheStatus.FAILED</code>.</li>
<li><code>directory</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type"><undefined></a> If the compile cache is enabled, this contains the directory
where the compile cache is stored. Only set if <code>status</code> is
<code>module.constants.compileCacheStatus.ENABLED</code> or
<code>module.constants.compileCacheStatus.ALREADY_ENABLED</code>.</li>
</ul>
</li>
</ul>
<p>Enable <a href="#module-compile-cache">module compile cache</a> in the current Node.js instance.</p>
<p>If <code>cacheDir</code> is not specified, Node.js will either use the directory specified by the
<a href="cli.html#node_compile_cachedir"><code>NODE_COMPILE_CACHE=dir</code></a> environment variable if it's set, or use
<code>path.join(os.tmpdir(), 'node-compile-cache')</code> otherwise. For general use cases, it's
recommended to call <code>module.enableCompileCache()</code> without specifying the <code>cacheDir</code>,
so that the directory can be overridden by the <code>NODE_COMPILE_CACHE</code> environment
variable when necessary.</p>
<p>Since compile cache is supposed to be a quiet optimization that is not required for the
application to be functional, this method is designed to not throw any exception when the
compile cache cannot be enabled. Instead, it will return an object containing an error
message in the <code>message</code> field to aid debugging.
If compile cache is enabled successfully, the <code>directory</code> field in the returned object
contains the path to the directory where the compile cache is stored. The <code>status</code>
field in the returned object would be one of the <code>module.constants.compileCacheStatus</code>
values to indicate the result of the attempt to enable the <a href="#module-compile-cache">module compile cache</a>.</p>
<p>This method only affects the current Node.js instance. To enable it in child worker threads,
either call this method in child worker threads too, or set the
<code>process.env.NODE_COMPILE_CACHE</code> value to compile cache directory so the behavior can
be inherited into the child workers. The directory can be obtained either from the
<code>directory</code> field returned by this method, or with <a href="#modulegetcompilecachedir"><code>module.getCompileCacheDir()</code></a>.</p>
<h4><code>module.flushCompileCache()</code><span><a class="mark" href="#moduleflushcompilecache" id="moduleflushcompilecache">#</a></span><a aria-hidden="true" class="legacy" id="module_module_flushcompilecache"></a></h4>
<div class="api_metadata">
<span>Added in: v23.0.0, v22.10.0</span>
</div>
<p></p><div class="api_stability api_stability_1"><a href="documentation.html#stability-index">Stability: 1</a>.1 - Active Development</div><p></p>
<p>Flush the <a href="#module-compile-cache">module compile cache</a> accumulated from modules already loaded
in the current Node.js instance to disk. This returns after all the flushing
file system operations come to an end, no matter they succeed or not. If there
are any errors, this will fail silently, since compile cache misses should not
interfere with the actual operation of the application.</p>
<h4><code>module.getCompileCacheDir()</code><span><a class="mark" href="#modulegetcompilecachedir_1" id="modulegetcompilecachedir_1">#</a></span><a aria-hidden="true" class="legacy" id="module_module_getcompilecachedir_1"></a></h4>
<div class="api_metadata">
<span>Added in: v22.8.0</span>
</div>
<p></p><div class="api_stability api_stability_1"><a href="documentation.html#stability-index">Stability: 1</a>.1 - Active Development</div><p></p>
<ul>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type"><undefined></a> Path to the <a href="#module-compile-cache">module compile cache</a> directory if it is enabled,
or <code>undefined</code> otherwise.</li>
</ul>
<p><i id="module_customization_hooks"></i></p>
</section><section><h3>Customization Hooks<span><a class="mark" href="#customization-hooks" id="customization-hooks">#</a></span><a aria-hidden="true" class="legacy" id="module_customization_hooks"></a></h3>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v20.6.0, v18.19.0</td>
<td><p>Added <code>initialize</code> hook to replace <code>globalPreload</code>.</p></td></tr>
<tr><td>v18.6.0, v16.17.0</td>
<td><p>Add support for chaining loaders.</p></td></tr>
<tr><td>v16.12.0</td>
<td><p>Removed <code>getFormat</code>, <code>getSource</code>, <code>transformSource</code>, and <code>globalPreload</code>; added <code>load</code> hook and <code>getGlobalPreload</code> hook.</p></td></tr>
<tr><td>v8.8.0</td>
<td><p><span>Added in: v8.8.0</span></p></td></tr>
</tbody></table>
</details>
</div>
<p></p><div class="api_stability api_stability_1"><a href="documentation.html#stability-index">Stability: 1</a>.2 - Release candidate</div><p></p>
<p><i id="enabling_module_customization_hooks"></i></p>
<h4>Enabling<span><a class="mark" href="#enabling" id="enabling">#</a></span><a aria-hidden="true" class="legacy" id="module_enabling"></a></h4>
<p>Module resolution and loading can be customized by registering a file which
exports a set of hooks. This can be done using the <a href="#moduleregisterspecifier-parenturl-options"><code>register</code></a> method
from <code>node:module</code>, which you can run before your application code by
using the <code>--import</code> flag:</p>
<pre><code class="language-bash">node --import ./register-hooks.js ./my-app.js</code> <button class="copy-button">copy</button></pre>
<pre class="with-44-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-comment">// register-hooks.js</span>
<span class="hljs-keyword">import</span> { register } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:module'</span>;
<span class="hljs-title function_">register</span>(<span class="hljs-string">'./hooks.mjs'</span>, <span class="hljs-keyword">import</span>.<span class="hljs-property">meta</span>.<span class="hljs-property">url</span>);</code><code class="language-js cjs"><span class="hljs-comment">// register-hooks.js</span>
<span class="hljs-keyword">const</span> { register } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:module'</span>);
<span class="hljs-keyword">const</span> { pathToFileURL } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:url'</span>);
<span class="hljs-title function_">register</span>(<span class="hljs-string">'./hooks.mjs'</span>, <span class="hljs-title function_">pathToFileURL</span>(__filename));</code><button class="copy-button">copy</button></pre>
<p>The file passed to <code>--import</code> can also be an export from a dependency:</p>
<pre><code class="language-bash">node --import some-package/register ./my-app.js</code> <button class="copy-button">copy</button></pre>
<p>Where <code>some-package</code> has an <a href="packages.html#exports"><code>"exports"</code></a> field defining the <code>/register</code>
export to map to a file that calls <code>register()</code>, like the following <code>register-hooks.js</code>
example.</p>
<p>Using <code>--import</code> ensures that the hooks are registered before any application
files are imported, including the entry point of the application. Alternatively,
<code>register</code> can be called from the entry point, but dynamic <code>import()</code> must be
used for any code that should be run after the hooks are registered:</p>
<pre class="with-46-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> { register } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:module'</span>;
<span class="hljs-title function_">register</span>(<span class="hljs-string">'http-to-https'</span>, <span class="hljs-keyword">import</span>.<span class="hljs-property">meta</span>.<span class="hljs-property">url</span>);
<span class="hljs-comment">// Because this is a dynamic `import()`, the `http-to-https` hooks will run</span>
<span class="hljs-comment">// to handle `./my-app.js` and any other files it imports or requires.</span>
<span class="hljs-keyword">await</span> <span class="hljs-keyword">import</span>(<span class="hljs-string">'./my-app.js'</span>);</code><code class="language-js cjs"><span class="hljs-keyword">const</span> { register } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:module'</span>);
<span class="hljs-keyword">const</span> { pathToFileURL } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:url'</span>);
<span class="hljs-title function_">register</span>(<span class="hljs-string">'http-to-https'</span>, <span class="hljs-title function_">pathToFileURL</span>(__filename));
<span class="hljs-comment">// Because this is a dynamic `import()`, the `http-to-https` hooks will run</span>
<span class="hljs-comment">// to handle `./my-app.js` and any other files it imports or requires.</span>
<span class="hljs-keyword">import</span>(<span class="hljs-string">'./my-app.js'</span>);</code><button class="copy-button">copy</button></pre>
<p>In this example, we are registering the <code>http-to-https</code> hooks, but they will
only be available for subsequently imported modules—in this case, <code>my-app.js</code>
and anything it references via <code>import</code> (and optionally <code>require</code>). If the
<code>import('./my-app.js')</code> had instead been a static <code>import './my-app.js'</code>, the
app would have <em>already</em> been loaded <strong>before</strong> the <code>http-to-https</code> hooks were
registered. This due to the ES modules specification, where static imports are
evaluated from the leaves of the tree first, then back to the trunk. There can
be static imports <em>within</em> <code>my-app.js</code>, which will not be evaluated until
<code>my-app.js</code> is dynamically imported.</p>
<p><code>my-app.js</code> can also be CommonJS. Customization hooks will run for any
modules that it references via <code>import</code> (and optionally <code>require</code>).</p>
<p>Finally, if all you want to do is register hooks before your app runs and you
don't want to create a separate file for that purpose, you can pass a <code>data:</code>
URL to <code>--import</code>:</p>
<pre><code class="language-bash">node --import <span class="hljs-string">'data:text/javascript,import { register } from "node:module"; import { pathToFileURL } from "node:url"; register("http-to-https", pathToFileURL("./"));'</span> ./my-app.js</code> <button class="copy-button">copy</button></pre>
<h4>Chaining<span><a class="mark" href="#chaining" id="chaining">#</a></span><a aria-hidden="true" class="legacy" id="module_chaining"></a></h4>
<p>It's possible to call <code>register</code> more than once:</p>
<pre class="with-44-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-comment">// entrypoint.mjs</span>
<span class="hljs-keyword">import</span> { register } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:module'</span>;
<span class="hljs-title function_">register</span>(<span class="hljs-string">'./foo.mjs'</span>, <span class="hljs-keyword">import</span>.<span class="hljs-property">meta</span>.<span class="hljs-property">url</span>);
<span class="hljs-title function_">register</span>(<span class="hljs-string">'./bar.mjs'</span>, <span class="hljs-keyword">import</span>.<span class="hljs-property">meta</span>.<span class="hljs-property">url</span>);
<span class="hljs-keyword">await</span> <span class="hljs-keyword">import</span>(<span class="hljs-string">'./my-app.mjs'</span>);</code><code class="language-js cjs"><span class="hljs-comment">// entrypoint.cjs</span>
<span class="hljs-keyword">const</span> { register } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:module'</span>);
<span class="hljs-keyword">const</span> { pathToFileURL } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:url'</span>);
<span class="hljs-keyword">const</span> parentURL = <span class="hljs-title function_">pathToFileURL</span>(__filename);
<span class="hljs-title function_">register</span>(<span class="hljs-string">'./foo.mjs'</span>, parentURL);
<span class="hljs-title function_">register</span>(<span class="hljs-string">'./bar.mjs'</span>, parentURL);
<span class="hljs-keyword">import</span>(<span class="hljs-string">'./my-app.mjs'</span>);</code><button class="copy-button">copy</button></pre>
<p>In this example, the registered hooks will form chains. These chains run
last-in, first out (LIFO). If both <code>foo.mjs</code> and <code>bar.mjs</code> define a <code>resolve</code>
hook, they will be called like so (note the right-to-left):
node's default ← <code>./foo.mjs</code> ← <code>./bar.mjs</code>
(starting with <code>./bar.mjs</code>, then <code>./foo.mjs</code>, then the Node.js default).
The same applies to all the other hooks.</p>
<p>The registered hooks also affect <code>register</code> itself. In this example,
<code>bar.mjs</code> will be resolved and loaded via the hooks registered by <code>foo.mjs</code>
(because <code>foo</code>'s hooks will have already been added to the chain). This allows
for things like writing hooks in non-JavaScript languages, so long as
earlier registered hooks transpile into JavaScript.</p>
<p>The <code>register</code> method cannot be called from within the module that defines the
hooks.</p>
<h4>Communication with module customization hooks<span><a class="mark" href="#communication-with-module-customization-hooks" id="communication-with-module-customization-hooks">#</a></span><a aria-hidden="true" class="legacy" id="module_communication_with_module_customization_hooks"></a></h4>
<p>Module customization hooks run on a dedicated thread, separate from the main
thread that runs application code. This means mutating global variables won't
affect the other thread(s), and message channels must be used to communicate
between the threads.</p>
<p>The <code>register</code> method can be used to pass data to an <a href="#initialize"><code>initialize</code></a> hook. The
data passed to the hook may include transferrable objects like ports.</p>
<pre class="with-53-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> { register } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:module'</span>;
<span class="hljs-keyword">import</span> { <span class="hljs-title class_">MessageChannel</span> } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:worker_threads'</span>;
<span class="hljs-comment">// This example demonstrates how a message channel can be used to</span>
<span class="hljs-comment">// communicate with the hooks, by sending `port2` to the hooks.</span>
<span class="hljs-keyword">const</span> { port1, port2 } = <span class="hljs-keyword">new</span> <span class="hljs-title class_">MessageChannel</span>();
port1.<span class="hljs-title function_">on</span>(<span class="hljs-string">'message'</span>, <span class="hljs-function">(<span class="hljs-params">msg</span>) =></span> {
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(msg);
});
port1.<span class="hljs-title function_">unref</span>();
<span class="hljs-title function_">register</span>(<span class="hljs-string">'./my-hooks.mjs'</span>, {
<span class="hljs-attr">parentURL</span>: <span class="hljs-keyword">import</span>.<span class="hljs-property">meta</span>.<span class="hljs-property">url</span>,
<span class="hljs-attr">data</span>: { <span class="hljs-attr">number</span>: <span class="hljs-number">1</span>, <span class="hljs-attr">port</span>: port2 },
<span class="hljs-attr">transferList</span>: [port2],
});</code><code class="language-js cjs"><span class="hljs-keyword">const</span> { register } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:module'</span>);
<span class="hljs-keyword">const</span> { pathToFileURL } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:url'</span>);
<span class="hljs-keyword">const</span> { <span class="hljs-title class_">MessageChannel</span> } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:worker_threads'</span>);
<span class="hljs-comment">// This example showcases how a message channel can be used to</span>
<span class="hljs-comment">// communicate with the hooks, by sending `port2` to the hooks.</span>
<span class="hljs-keyword">const</span> { port1, port2 } = <span class="hljs-keyword">new</span> <span class="hljs-title class_">MessageChannel</span>();
port1.<span class="hljs-title function_">on</span>(<span class="hljs-string">'message'</span>, <span class="hljs-function">(<span class="hljs-params">msg</span>) =></span> {
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(msg);
});
port1.<span class="hljs-title function_">unref</span>();
<span class="hljs-title function_">register</span>(<span class="hljs-string">'./my-hooks.mjs'</span>, {
<span class="hljs-attr">parentURL</span>: <span class="hljs-title function_">pathToFileURL</span>(__filename),
<span class="hljs-attr">data</span>: { <span class="hljs-attr">number</span>: <span class="hljs-number">1</span>, <span class="hljs-attr">port</span>: port2 },
<span class="hljs-attr">transferList</span>: [port2],
});</code><button class="copy-button">copy</button></pre>
<h4>Hooks<span><a class="mark" href="#hooks" id="hooks">#</a></span><a aria-hidden="true" class="legacy" id="module_hooks"></a></h4>
<p>The <a href="#moduleregisterspecifier-parenturl-options"><code>register</code></a> method can be used to register a module that exports a set of
hooks. The hooks are functions that are called by Node.js to customize the
module resolution and loading process. The exported functions must have specific
names and signatures, and they must be exported as named exports.</p>
<pre><code class="language-js mjs"><span class="hljs-keyword">export</span> <span class="hljs-keyword">async</span> <span class="hljs-keyword">function</span> <span class="hljs-title function_">initialize</span>(<span class="hljs-params">{ number, port }</span>) {
<span class="hljs-comment">// Receives data from `register`.</span>
}
<span class="hljs-keyword">export</span> <span class="hljs-keyword">async</span> <span class="hljs-keyword">function</span> <span class="hljs-title function_">resolve</span>(<span class="hljs-params">specifier, context, nextResolve</span>) {
<span class="hljs-comment">// Take an `import` or `require` specifier and resolve it to a URL.</span>
}
<span class="hljs-keyword">export</span> <span class="hljs-keyword">async</span> <span class="hljs-keyword">function</span> <span class="hljs-title function_">load</span>(<span class="hljs-params">url, context, nextLoad</span>) {
<span class="hljs-comment">// Take a resolved URL and return the source code to be evaluated.</span>
}</code> <button class="copy-button">copy</button></pre>
<p>Hooks are part of a <a href="#chaining">chain</a>, even if that chain consists of only one
custom (user-provided) hook and the default hook, which is always present. Hook
functions nest: each one must always return a plain object, and chaining happens
as a result of each function calling <code>next<hookName>()</code>, which is a reference to
the subsequent loader's hook (in LIFO order).</p>
<p>A hook that returns a value lacking a required property triggers an exception. A
hook that returns without calling <code>next<hookName>()</code> <em>and</em> without returning
<code>shortCircuit: true</code> also triggers an exception. These errors are to help
prevent unintentional breaks in the chain. Return <code>shortCircuit: true</code> from a
hook to signal that the chain is intentionally ending at your hook.</p>
<p>Hooks are run in a separate thread, isolated from the main thread where
application code runs. That means it is a different <a href="https://tc39.es/ecma262/#realm">realm</a>. The hooks thread
may be terminated by the main thread at any time, so do not depend on
asynchronous operations (like <code>console.log</code>) to complete.</p>
<h5><code>initialize()</code><span><a class="mark" href="#initialize" id="initialize">#</a></span><a aria-hidden="true" class="legacy" id="module_initialize"></a></h5>
<div class="api_metadata">
<span>Added in: v20.6.0, v18.19.0</span>
</div>
<p></p><div class="api_stability api_stability_1"><a href="documentation.html#stability-index">Stability: 1</a>.2 - Release candidate</div><p></p>
<ul>
<li><code>data</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Data_types" class="type"><any></a> The data from <code>register(loader, import.meta.url, { data })</code>.</li>
</ul>
<p>The <code>initialize</code> hook provides a way to define a custom function that runs in
the hooks thread when the hooks module is initialized. Initialization happens
when the hooks module is registered via <a href="#moduleregisterspecifier-parenturl-options"><code>register</code></a>.</p>
<p>This hook can receive data from a <a href="#moduleregisterspecifier-parenturl-options"><code>register</code></a> invocation, including
ports and other transferrable objects. The return value of <code>initialize</code> can be a
<a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise" class="type"><Promise></a>, in which case it will be awaited before the main application thread
execution resumes.</p>
<p>Module customization code:</p>
<pre><code class="language-js mjs"><span class="hljs-comment">// path-to-my-hooks.js</span>
<span class="hljs-keyword">export</span> <span class="hljs-keyword">async</span> <span class="hljs-keyword">function</span> <span class="hljs-title function_">initialize</span>(<span class="hljs-params">{ number, port }</span>) {
port.<span class="hljs-title function_">postMessage</span>(<span class="hljs-string">`increment: <span class="hljs-subst">${number + <span class="hljs-number">1</span>}</span>`</span>);
}</code> <button class="copy-button">copy</button></pre>
<p>Caller code:</p>
<pre class="with-44-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-keyword">import</span> assert <span class="hljs-keyword">from</span> <span class="hljs-string">'node:assert'</span>;
<span class="hljs-keyword">import</span> { register } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:module'</span>;
<span class="hljs-keyword">import</span> { <span class="hljs-title class_">MessageChannel</span> } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:worker_threads'</span>;
<span class="hljs-comment">// This example showcases how a message channel can be used to communicate</span>
<span class="hljs-comment">// between the main (application) thread and the hooks running on the hooks</span>
<span class="hljs-comment">// thread, by sending `port2` to the `initialize` hook.</span>
<span class="hljs-keyword">const</span> { port1, port2 } = <span class="hljs-keyword">new</span> <span class="hljs-title class_">MessageChannel</span>();
port1.<span class="hljs-title function_">on</span>(<span class="hljs-string">'message'</span>, <span class="hljs-function">(<span class="hljs-params">msg</span>) =></span> {
assert.<span class="hljs-title function_">strictEqual</span>(msg, <span class="hljs-string">'increment: 2'</span>);
});
port1.<span class="hljs-title function_">unref</span>();
<span class="hljs-title function_">register</span>(<span class="hljs-string">'./path-to-my-hooks.js'</span>, {
<span class="hljs-attr">parentURL</span>: <span class="hljs-keyword">import</span>.<span class="hljs-property">meta</span>.<span class="hljs-property">url</span>,
<span class="hljs-attr">data</span>: { <span class="hljs-attr">number</span>: <span class="hljs-number">1</span>, <span class="hljs-attr">port</span>: port2 },
<span class="hljs-attr">transferList</span>: [port2],
});</code><code class="language-js cjs"><span class="hljs-keyword">const</span> assert = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:assert'</span>);
<span class="hljs-keyword">const</span> { register } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:module'</span>);
<span class="hljs-keyword">const</span> { pathToFileURL } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:url'</span>);
<span class="hljs-keyword">const</span> { <span class="hljs-title class_">MessageChannel</span> } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:worker_threads'</span>);
<span class="hljs-comment">// This example showcases how a message channel can be used to communicate</span>
<span class="hljs-comment">// between the main (application) thread and the hooks running on the hooks</span>
<span class="hljs-comment">// thread, by sending `port2` to the `initialize` hook.</span>
<span class="hljs-keyword">const</span> { port1, port2 } = <span class="hljs-keyword">new</span> <span class="hljs-title class_">MessageChannel</span>();
port1.<span class="hljs-title function_">on</span>(<span class="hljs-string">'message'</span>, <span class="hljs-function">(<span class="hljs-params">msg</span>) =></span> {
assert.<span class="hljs-title function_">strictEqual</span>(msg, <span class="hljs-string">'increment: 2'</span>);
});
port1.<span class="hljs-title function_">unref</span>();
<span class="hljs-title function_">register</span>(<span class="hljs-string">'./path-to-my-hooks.js'</span>, {
<span class="hljs-attr">parentURL</span>: <span class="hljs-title function_">pathToFileURL</span>(__filename),
<span class="hljs-attr">data</span>: { <span class="hljs-attr">number</span>: <span class="hljs-number">1</span>, <span class="hljs-attr">port</span>: port2 },
<span class="hljs-attr">transferList</span>: [port2],
});</code><button class="copy-button">copy</button></pre>
<h5><code>resolve(specifier, context, nextResolve)</code><span><a class="mark" href="#resolvespecifier-context-nextresolve" id="resolvespecifier-context-nextresolve">#</a></span><a aria-hidden="true" class="legacy" id="module_resolve_specifier_context_nextresolve"></a></h5>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v21.0.0, v20.10.0, v18.19.0</td>
<td><p>The property <code>context.importAssertions</code> is replaced with <code>context.importAttributes</code>. Using the old name is still supported and will emit an experimental warning.</p></td></tr>
<tr><td>v18.6.0, v16.17.0</td>
<td><p>Add support for chaining resolve hooks. Each hook must either call <code>nextResolve()</code> or include a <code>shortCircuit</code> property set to <code>true</code> in its return.</p></td></tr>
<tr><td>v17.1.0, v16.14.0</td>
<td><p>Add support for import assertions.</p></td></tr>
</tbody></table>
</details>
</div>
<p></p><div class="api_stability api_stability_1"><a href="documentation.html#stability-index">Stability: 1</a>.2 - Release candidate</div><p></p>
<ul>
<li><code>specifier</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li>
<li><code>context</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a>
<ul>
<li><code>conditions</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string[]></a> Export conditions of the relevant <code>package.json</code></li>
<li><code>importAttributes</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> An object whose key-value pairs represent the
attributes for the module to import</li>
<li><code>parentURL</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type"><undefined></a> The module importing this one, or undefined
if this is the Node.js entry point</li>
</ul>
</li>
<li><code>nextResolve</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> The subsequent <code>resolve</code> hook in the chain, or the
Node.js default <code>resolve</code> hook after the last user-supplied <code>resolve</code> hook
<ul>
<li><code>specifier</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li>
<li><code>context</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li>
</ul>
</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise" class="type"><Promise></a>
<ul>
<li><code>format</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type" class="type"><null></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type"><undefined></a> A hint to the load hook (it might be
ignored)
<code>'builtin' | 'commonjs' | 'json' | 'module' | 'wasm'</code></li>
<li><code>importAttributes</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type"><undefined></a> The import attributes to use when
caching the module (optional; if excluded the input will be used)</li>
<li><code>shortCircuit</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type"><undefined></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> A signal that this hook intends to
terminate the chain of <code>resolve</code> hooks. <strong>Default:</strong> <code>false</code></li>
<li><code>url</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> The absolute URL to which this input resolves</li>
</ul>
</li>
</ul>
<blockquote>
<p><strong>Warning</strong> Despite support for returning promises and async functions, calls
to <code>resolve</code> may block the main thread which can impact performance.</p>
</blockquote>
<p>The <code>resolve</code> hook chain is responsible for telling Node.js where to find and
how to cache a given <code>import</code> statement or expression, or <code>require</code> call. It can
optionally return a format (such as <code>'module'</code>) as a hint to the <code>load</code> hook. If
a format is specified, the <code>load</code> hook is ultimately responsible for providing
the final <code>format</code> value (and it is free to ignore the hint provided by
<code>resolve</code>); if <code>resolve</code> provides a <code>format</code>, a custom <code>load</code> hook is required
even if only to pass the value to the Node.js default <code>load</code> hook.</p>
<p>Import type attributes are part of the cache key for saving loaded modules into
the internal module cache. The <code>resolve</code> hook is responsible for returning an
<code>importAttributes</code> object if the module should be cached with different
attributes than were present in the source code.</p>
<p>The <code>conditions</code> property in <code>context</code> is an array of conditions for
<a href="packages.html#conditional-exports">package exports conditions</a> that apply to this resolution
request. They can be used for looking up conditional mappings elsewhere or to
modify the list when calling the default resolution logic.</p>
<p>The current <a href="packages.html#conditional-exports">package exports conditions</a> are always in
the <code>context.conditions</code> array passed into the hook. To guarantee <em>default
Node.js module specifier resolution behavior</em> when calling <code>defaultResolve</code>, the
<code>context.conditions</code> array passed to it <em>must</em> include <em>all</em> elements of the
<code>context.conditions</code> array originally passed into the <code>resolve</code> hook.</p>
<pre><code class="language-js mjs"><span class="hljs-keyword">export</span> <span class="hljs-keyword">async</span> <span class="hljs-keyword">function</span> <span class="hljs-title function_">resolve</span>(<span class="hljs-params">specifier, context, nextResolve</span>) {
<span class="hljs-keyword">const</span> { parentURL = <span class="hljs-literal">null</span> } = context;
<span class="hljs-keyword">if</span> (<span class="hljs-title class_">Math</span>.<span class="hljs-title function_">random</span>() > <span class="hljs-number">0.5</span>) { <span class="hljs-comment">// Some condition.</span>
<span class="hljs-comment">// For some or all specifiers, do some custom logic for resolving.</span>
<span class="hljs-comment">// Always return an object of the form {url: <string>}.</span>
<span class="hljs-keyword">return</span> {
<span class="hljs-attr">shortCircuit</span>: <span class="hljs-literal">true</span>,
<span class="hljs-attr">url</span>: parentURL ?
<span class="hljs-keyword">new</span> <span class="hljs-title function_">URL</span>(specifier, parentURL).<span class="hljs-property">href</span> :
<span class="hljs-keyword">new</span> <span class="hljs-title function_">URL</span>(specifier).<span class="hljs-property">href</span>,
};
}
<span class="hljs-keyword">if</span> (<span class="hljs-title class_">Math</span>.<span class="hljs-title function_">random</span>() < <span class="hljs-number">0.5</span>) { <span class="hljs-comment">// Another condition.</span>
<span class="hljs-comment">// When calling `defaultResolve`, the arguments can be modified. In this</span>
<span class="hljs-comment">// case it's adding another value for matching conditional exports.</span>
<span class="hljs-keyword">return</span> <span class="hljs-title function_">nextResolve</span>(specifier, {
...context,
<span class="hljs-attr">conditions</span>: [...context.<span class="hljs-property">conditions</span>, <span class="hljs-string">'another-condition'</span>],
});
}
<span class="hljs-comment">// Defer to the next hook in the chain, which would be the</span>
<span class="hljs-comment">// Node.js default resolve if this is the last user-specified loader.</span>
<span class="hljs-keyword">return</span> <span class="hljs-title function_">nextResolve</span>(specifier);
}</code> <button class="copy-button">copy</button></pre>
<h5><code>load(url, context, nextLoad)</code><span><a class="mark" href="#loadurl-context-nextload" id="loadurl-context-nextload">#</a></span><a aria-hidden="true" class="legacy" id="module_load_url_context_nextload"></a></h5>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v20.6.0</td>
<td><p>Add support for <code>source</code> with format <code>commonjs</code>.</p></td></tr>
<tr><td>v18.6.0, v16.17.0</td>
<td><p>Add support for chaining load hooks. Each hook must either call <code>nextLoad()</code> or include a <code>shortCircuit</code> property set to <code>true</code> in its return.</p></td></tr>
</tbody></table>
</details>
</div>
<p></p><div class="api_stability api_stability_1"><a href="documentation.html#stability-index">Stability: 1</a>.2 - Release candidate</div><p></p>
<ul>
<li><code>url</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> The URL returned by the <code>resolve</code> chain</li>
<li><code>context</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a>
<ul>
<li><code>conditions</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string[]></a> Export conditions of the relevant <code>package.json</code></li>
<li><code>format</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Null_type" class="type"><null></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type"><undefined></a> The format optionally supplied by the
<code>resolve</code> hook chain</li>
<li><code>importAttributes</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li>
</ul>
</li>
<li><code>nextLoad</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a> The subsequent <code>load</code> hook in the chain, or the
Node.js default <code>load</code> hook after the last user-supplied <code>load</code> hook
<ul>
<li><code>url</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li>
<li><code>context</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li>
</ul>
</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a>
<ul>
<li><code>format</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li>
<li><code>shortCircuit</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type"><undefined></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> A signal that this hook intends to
terminate the chain of <code>load</code> hooks. <strong>Default:</strong> <code>false</code></li>
<li><code>source</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer" class="type"><ArrayBuffer></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray" class="type"><TypedArray></a> The source for Node.js to evaluate</li>
</ul>
</li>
</ul>
<p>The <code>load</code> hook provides a way to define a custom method of determining how a
URL should be interpreted, retrieved, and parsed. It is also in charge of
validating the import attributes.</p>
<p>The final value of <code>format</code> must be one of the following:</p>
<table><thead><tr><th><code>format</code></th><th>Description</th><th>Acceptable types for <code>source</code> returned by <code>load</code></th></tr></thead><tbody><tr><td><code>'builtin'</code></td><td>Load a Node.js builtin module</td><td>Not applicable</td></tr><tr><td><code>'commonjs'</code></td><td>Load a Node.js CommonJS module</td><td>{ <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String"><code>string</code></a>, <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer"><code>ArrayBuffer</code></a>, <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray"><code>TypedArray</code></a>, <code>null</code>, <code>undefined</code> }</td></tr><tr><td><code>'json'</code></td><td>Load a JSON file</td><td>{ <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String"><code>string</code></a>, <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer"><code>ArrayBuffer</code></a>, <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray"><code>TypedArray</code></a> }</td></tr><tr><td><code>'module'</code></td><td>Load an ES module</td><td>{ <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String"><code>string</code></a>, <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer"><code>ArrayBuffer</code></a>, <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray"><code>TypedArray</code></a> }</td></tr><tr><td><code>'wasm'</code></td><td>Load a WebAssembly module</td><td>{ <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer"><code>ArrayBuffer</code></a>, <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray"><code>TypedArray</code></a> }</td></tr></tbody></table>
<p>The value of <code>source</code> is ignored for type <code>'builtin'</code> because currently it is
not possible to replace the value of a Node.js builtin (core) module.</p>
<p>Omitting vs providing a <code>source</code> for <code>'commonjs'</code> has very different effects:</p>
<ul>
<li>When a <code>source</code> is provided, all <code>require</code> calls from this module will be
processed by the ESM loader with registered <code>resolve</code> and <code>load</code> hooks; all
<code>require.resolve</code> calls from this module will be processed by the ESM loader
with registered <code>resolve</code> hooks; only a subset of the CommonJS API will be
available (e.g. no <code>require.extensions</code>, no <code>require.cache</code>, no
<code>require.resolve.paths</code>) and monkey-patching on the CommonJS module loader
will not apply.</li>
<li>If <code>source</code> is undefined or <code>null</code>, it will be handled by the CommonJS module
loader and <code>require</code>/<code>require.resolve</code> calls will not go through the
registered hooks. This behavior for nullish <code>source</code> is temporary — in the
future, nullish <code>source</code> will not be supported.</li>
</ul>
<p>When <code>node</code> is run with <code>--experimental-default-type=commonjs</code>, the Node.js
internal <code>load</code> implementation, which is the value of <code>next</code> for the
last hook in the <code>load</code> chain, returns <code>null</code> for <code>source</code> when <code>format</code> is
<code>'commonjs'</code> for backward compatibility. Here is an example hook that would
opt-in to using the non-default behavior:</p>
<pre><code class="language-js mjs"><span class="hljs-keyword">import</span> { readFile } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:fs/promises'</span>;
<span class="hljs-keyword">export</span> <span class="hljs-keyword">async</span> <span class="hljs-keyword">function</span> <span class="hljs-title function_">load</span>(<span class="hljs-params">url, context, nextLoad</span>) {
<span class="hljs-keyword">const</span> result = <span class="hljs-keyword">await</span> <span class="hljs-title function_">nextLoad</span>(url, context);
<span class="hljs-keyword">if</span> (result.<span class="hljs-property">format</span> === <span class="hljs-string">'commonjs'</span>) {
result.<span class="hljs-property">source</span> ??= <span class="hljs-keyword">await</span> <span class="hljs-title function_">readFile</span>(<span class="hljs-keyword">new</span> <span class="hljs-title function_">URL</span>(result.<span class="hljs-property">responseURL</span> ?? url));
}
<span class="hljs-keyword">return</span> result;
}</code> <button class="copy-button">copy</button></pre>
<blockquote>
<p><strong>Warning</strong>: The ESM <code>load</code> hook and namespaced exports from CommonJS modules
are incompatible. Attempting to use them together will result in an empty
object from the import. This may be addressed in the future.</p>
</blockquote>
<blockquote>
<p>These types all correspond to classes defined in ECMAScript.</p>
</blockquote>
<ul>
<li>The specific <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer"><code>ArrayBuffer</code></a> object is a <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/SharedArrayBuffer"><code>SharedArrayBuffer</code></a>.</li>
<li>The specific <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypedArray"><code>TypedArray</code></a> object is a <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Uint8Array"><code>Uint8Array</code></a>.</li>
</ul>
<p>If the source value of a text-based format (i.e., <code>'json'</code>, <code>'module'</code>)
is not a string, it is converted to a string using <a href="util.html#class-utiltextdecoder"><code>util.TextDecoder</code></a>.</p>
<p>The <code>load</code> hook provides a way to define a custom method for retrieving the
source code of a resolved URL. This would allow a loader to potentially avoid
reading files from disk. It could also be used to map an unrecognized format to
a supported one, for example <code>yaml</code> to <code>module</code>.</p>
<pre><code class="language-js mjs"><span class="hljs-keyword">export</span> <span class="hljs-keyword">async</span> <span class="hljs-keyword">function</span> <span class="hljs-title function_">load</span>(<span class="hljs-params">url, context, nextLoad</span>) {
<span class="hljs-keyword">const</span> { format } = context;
<span class="hljs-keyword">if</span> (<span class="hljs-title class_">Math</span>.<span class="hljs-title function_">random</span>() > <span class="hljs-number">0.5</span>) { <span class="hljs-comment">// Some condition</span>
<span class="hljs-comment">/*
For some or all URLs, do some custom logic for retrieving the source.
Always return an object of the form {
format: <string>,
source: <string|buffer>,
}.
*/</span>
<span class="hljs-keyword">return</span> {
format,
<span class="hljs-attr">shortCircuit</span>: <span class="hljs-literal">true</span>,
<span class="hljs-attr">source</span>: <span class="hljs-string">'...'</span>,
};
}
<span class="hljs-comment">// Defer to the next hook in the chain.</span>
<span class="hljs-keyword">return</span> <span class="hljs-title function_">nextLoad</span>(url);
}</code> <button class="copy-button">copy</button></pre>
<p>In a more advanced scenario, this can also be used to transform an unsupported
source to a supported one (see <a href="#examples">Examples</a> below).</p>
<h4>Examples<span><a class="mark" href="#examples" id="examples">#</a></span><a aria-hidden="true" class="legacy" id="module_examples"></a></h4>
<p>The various module customization hooks can be used together to accomplish
wide-ranging customizations of the Node.js code loading and evaluation
behaviors.</p>
<h5>Import from HTTPS<span><a class="mark" href="#import-from-https" id="import-from-https">#</a></span><a aria-hidden="true" class="legacy" id="module_import_from_https"></a></h5>
<p>The hook below registers hooks to enable rudimentary support for such
specifiers. While this may seem like a significant improvement to Node.js core
functionality, there are substantial downsides to actually using these hooks:
performance is much slower than loading files from disk, there is no caching,
and there is no security.</p>
<pre><code class="language-js mjs"><span class="hljs-comment">// https-hooks.mjs</span>
<span class="hljs-keyword">import</span> { get } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:https'</span>;
<span class="hljs-keyword">export</span> <span class="hljs-keyword">function</span> <span class="hljs-title function_">load</span>(<span class="hljs-params">url, context, nextLoad</span>) {
<span class="hljs-comment">// For JavaScript to be loaded over the network, we need to fetch and</span>
<span class="hljs-comment">// return it.</span>
<span class="hljs-keyword">if</span> (url.<span class="hljs-title function_">startsWith</span>(<span class="hljs-string">'https://'</span>)) {
<span class="hljs-keyword">return</span> <span class="hljs-keyword">new</span> <span class="hljs-title class_">Promise</span>(<span class="hljs-function">(<span class="hljs-params">resolve, reject</span>) =></span> {
<span class="hljs-title function_">get</span>(url, <span class="hljs-function">(<span class="hljs-params">res</span>) =></span> {
<span class="hljs-keyword">let</span> data = <span class="hljs-string">''</span>;
res.<span class="hljs-title function_">setEncoding</span>(<span class="hljs-string">'utf8'</span>);
res.<span class="hljs-title function_">on</span>(<span class="hljs-string">'data'</span>, <span class="hljs-function">(<span class="hljs-params">chunk</span>) =></span> data += chunk);
res.<span class="hljs-title function_">on</span>(<span class="hljs-string">'end'</span>, <span class="hljs-function">() =></span> <span class="hljs-title function_">resolve</span>({
<span class="hljs-comment">// This example assumes all network-provided JavaScript is ES module</span>
<span class="hljs-comment">// code.</span>
<span class="hljs-attr">format</span>: <span class="hljs-string">'module'</span>,
<span class="hljs-attr">shortCircuit</span>: <span class="hljs-literal">true</span>,
<span class="hljs-attr">source</span>: data,
}));
}).<span class="hljs-title function_">on</span>(<span class="hljs-string">'error'</span>, <span class="hljs-function">(<span class="hljs-params">err</span>) =></span> <span class="hljs-title function_">reject</span>(err));
});
}
<span class="hljs-comment">// Let Node.js handle all other URLs.</span>
<span class="hljs-keyword">return</span> <span class="hljs-title function_">nextLoad</span>(url);
}</code> <button class="copy-button">copy</button></pre>
<pre><code class="language-js mjs"><span class="hljs-comment">// main.mjs</span>
<span class="hljs-keyword">import</span> { <span class="hljs-variable constant_">VERSION</span> } <span class="hljs-keyword">from</span> <span class="hljs-string">'https://coffeescript.org/browser-compiler-modern/coffeescript.js'</span>;
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-variable constant_">VERSION</span>);</code> <button class="copy-button">copy</button></pre>
<p>With the preceding hooks module, running
<code>node --import 'data:text/javascript,import { register } from "node:module"; import { pathToFileURL } from "node:url"; register(pathToFileURL("./https-hooks.mjs"));' ./main.mjs</code>
prints the current version of CoffeeScript per the module at the URL in
<code>main.mjs</code>.</p>
<h5>Transpilation<span><a class="mark" href="#transpilation" id="transpilation">#</a></span><a aria-hidden="true" class="legacy" id="module_transpilation"></a></h5>
<p>Sources that are in formats Node.js doesn't understand can be converted into
JavaScript using the <a href="#loadurl-context-nextload"><code>load</code> hook</a>.</p>
<p>This is less performant than transpiling source files before running Node.js;
transpiler hooks should only be used for development and testing purposes.</p>
<pre><code class="language-js mjs"><span class="hljs-comment">// coffeescript-hooks.mjs</span>
<span class="hljs-keyword">import</span> { readFile } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:fs/promises'</span>;
<span class="hljs-keyword">import</span> { dirname, extname, resolve <span class="hljs-keyword">as</span> resolvePath } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:path'</span>;
<span class="hljs-keyword">import</span> { cwd } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:process'</span>;
<span class="hljs-keyword">import</span> { fileURLToPath, pathToFileURL } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:url'</span>;
<span class="hljs-keyword">import</span> coffeescript <span class="hljs-keyword">from</span> <span class="hljs-string">'coffeescript'</span>;
<span class="hljs-keyword">const</span> extensionsRegex = <span class="hljs-regexp">/\.(coffee|litcoffee|coffee\.md)$/</span>;
<span class="hljs-keyword">export</span> <span class="hljs-keyword">async</span> <span class="hljs-keyword">function</span> <span class="hljs-title function_">load</span>(<span class="hljs-params">url, context, nextLoad</span>) {
<span class="hljs-keyword">if</span> (extensionsRegex.<span class="hljs-title function_">test</span>(url)) {
<span class="hljs-comment">// CoffeeScript files can be either CommonJS or ES modules, so we want any</span>
<span class="hljs-comment">// CoffeeScript file to be treated by Node.js the same as a .js file at the</span>
<span class="hljs-comment">// same location. To determine how Node.js would interpret an arbitrary .js</span>
<span class="hljs-comment">// file, search up the file system for the nearest parent package.json file</span>
<span class="hljs-comment">// and read its "type" field.</span>
<span class="hljs-keyword">const</span> format = <span class="hljs-keyword">await</span> <span class="hljs-title function_">getPackageType</span>(url);
<span class="hljs-keyword">const</span> { <span class="hljs-attr">source</span>: rawSource } = <span class="hljs-keyword">await</span> <span class="hljs-title function_">nextLoad</span>(url, { ...context, format });
<span class="hljs-comment">// This hook converts CoffeeScript source code into JavaScript source code</span>
<span class="hljs-comment">// for all imported CoffeeScript files.</span>
<span class="hljs-keyword">const</span> transformedSource = coffeescript.<span class="hljs-title function_">compile</span>(rawSource.<span class="hljs-title function_">toString</span>(), url);
<span class="hljs-keyword">return</span> {
format,
<span class="hljs-attr">shortCircuit</span>: <span class="hljs-literal">true</span>,
<span class="hljs-attr">source</span>: transformedSource,
};
}
<span class="hljs-comment">// Let Node.js handle all other URLs.</span>
<span class="hljs-keyword">return</span> <span class="hljs-title function_">nextLoad</span>(url);
}
<span class="hljs-keyword">async</span> <span class="hljs-keyword">function</span> <span class="hljs-title function_">getPackageType</span>(<span class="hljs-params">url</span>) {
<span class="hljs-comment">// `url` is only a file path during the first iteration when passed the</span>
<span class="hljs-comment">// resolved url from the load() hook</span>
<span class="hljs-comment">// an actual file path from load() will contain a file extension as it's</span>
<span class="hljs-comment">// required by the spec</span>
<span class="hljs-comment">// this simple truthy check for whether `url` contains a file extension will</span>
<span class="hljs-comment">// work for most projects but does not cover some edge-cases (such as</span>
<span class="hljs-comment">// extensionless files or a url ending in a trailing space)</span>
<span class="hljs-keyword">const</span> isFilePath = !!<span class="hljs-title function_">extname</span>(url);
<span class="hljs-comment">// If it is a file path, get the directory it's in</span>
<span class="hljs-keyword">const</span> dir = isFilePath ?
<span class="hljs-title function_">dirname</span>(<span class="hljs-title function_">fileURLToPath</span>(url)) :
url;
<span class="hljs-comment">// Compose a file path to a package.json in the same directory,</span>
<span class="hljs-comment">// which may or may not exist</span>
<span class="hljs-keyword">const</span> packagePath = <span class="hljs-title function_">resolvePath</span>(dir, <span class="hljs-string">'package.json'</span>);
<span class="hljs-comment">// Try to read the possibly nonexistent package.json</span>
<span class="hljs-keyword">const</span> type = <span class="hljs-keyword">await</span> <span class="hljs-title function_">readFile</span>(packagePath, { <span class="hljs-attr">encoding</span>: <span class="hljs-string">'utf8'</span> })
.<span class="hljs-title function_">then</span>(<span class="hljs-function">(<span class="hljs-params">filestring</span>) =></span> <span class="hljs-title class_">JSON</span>.<span class="hljs-title function_">parse</span>(filestring).<span class="hljs-property">type</span>)
.<span class="hljs-title function_">catch</span>(<span class="hljs-function">(<span class="hljs-params">err</span>) =></span> {
<span class="hljs-keyword">if</span> (err?.<span class="hljs-property">code</span> !== <span class="hljs-string">'ENOENT'</span>) <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">error</span>(err);
});
<span class="hljs-comment">// If package.json existed and contained a `type` field with a value, voilà</span>
<span class="hljs-keyword">if</span> (type) <span class="hljs-keyword">return</span> type;
<span class="hljs-comment">// Otherwise, (if not at the root) continue checking the next directory up</span>
<span class="hljs-comment">// If at the root, stop and return false</span>
<span class="hljs-keyword">return</span> dir.<span class="hljs-property">length</span> > <span class="hljs-number">1</span> && <span class="hljs-title function_">getPackageType</span>(<span class="hljs-title function_">resolvePath</span>(dir, <span class="hljs-string">'..'</span>));
}</code> <button class="copy-button">copy</button></pre>
<pre><code class="language-coffee"><span class="hljs-comment"># main.coffee</span>
<span class="hljs-keyword">import</span> { scream } <span class="hljs-keyword">from</span> <span class="hljs-string">'./scream.coffee'</span>
console.log scream <span class="hljs-string">'hello, world'</span>
<span class="hljs-keyword">import</span> { version } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:process'</span>
console.log <span class="hljs-string">"Brought to you by Node.js version <span class="hljs-subst">#{version}</span>"</span></code> <button class="copy-button">copy</button></pre>
<pre><code class="language-coffee"><span class="hljs-comment"># scream.coffee</span>
<span class="hljs-keyword">export</span> scream = <span class="hljs-function"><span class="hljs-params">(str)</span> -></span> str.toUpperCase()</code> <button class="copy-button">copy</button></pre>
<p>With the preceding hooks module, running
<code>node --import 'data:text/javascript,import { register } from "node:module"; import { pathToFileURL } from "node:url"; register(pathToFileURL("./coffeescript-hooks.mjs"));' ./main.coffee</code>
causes <code>main.coffee</code> to be turned into JavaScript after its source code is
loaded from disk but before Node.js executes it; and so on for any <code>.coffee</code>,
<code>.litcoffee</code> or <code>.coffee.md</code> files referenced via <code>import</code> statements of any
loaded file.</p>
<h5>Import maps<span><a class="mark" href="#import-maps" id="import-maps">#</a></span><a aria-hidden="true" class="legacy" id="module_import_maps"></a></h5>
<p>The previous two examples defined <code>load</code> hooks. This is an example of a
<code>resolve</code> hook. This hooks module reads an <code>import-map.json</code> file that defines
which specifiers to override to other URLs (this is a very simplistic
implementation of a small subset of the "import maps" specification).</p>
<pre><code class="language-js mjs"><span class="hljs-comment">// import-map-hooks.js</span>
<span class="hljs-keyword">import</span> fs <span class="hljs-keyword">from</span> <span class="hljs-string">'node:fs/promises'</span>;
<span class="hljs-keyword">const</span> { imports } = <span class="hljs-title class_">JSON</span>.<span class="hljs-title function_">parse</span>(<span class="hljs-keyword">await</span> fs.<span class="hljs-title function_">readFile</span>(<span class="hljs-string">'import-map.json'</span>));
<span class="hljs-keyword">export</span> <span class="hljs-keyword">async</span> <span class="hljs-keyword">function</span> <span class="hljs-title function_">resolve</span>(<span class="hljs-params">specifier, context, nextResolve</span>) {
<span class="hljs-keyword">if</span> (<span class="hljs-title class_">Object</span>.<span class="hljs-title function_">hasOwn</span>(imports, specifier)) {
<span class="hljs-keyword">return</span> <span class="hljs-title function_">nextResolve</span>(imports[specifier], context);
}
<span class="hljs-keyword">return</span> <span class="hljs-title function_">nextResolve</span>(specifier, context);
}</code> <button class="copy-button">copy</button></pre>
<p>With these files:</p>
<pre><code class="language-js mjs"><span class="hljs-comment">// main.js</span>
<span class="hljs-keyword">import</span> <span class="hljs-string">'a-module'</span>;</code> <button class="copy-button">copy</button></pre>
<pre><code class="language-json"><span class="hljs-comment">// import-map.json</span>
<span class="hljs-punctuation">{</span>
<span class="hljs-attr">"imports"</span><span class="hljs-punctuation">:</span> <span class="hljs-punctuation">{</span>
<span class="hljs-attr">"a-module"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./some-module.js"</span>
<span class="hljs-punctuation">}</span>
<span class="hljs-punctuation">}</span></code> <button class="copy-button">copy</button></pre>
<pre><code class="language-js mjs"><span class="hljs-comment">// some-module.js</span>
<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-string">'some module!'</span>);</code> <button class="copy-button">copy</button></pre>
<p>Running <code>node --import 'data:text/javascript,import { register } from "node:module"; import { pathToFileURL } from "node:url"; register(pathToFileURL("./import-map-hooks.js"));' main.js</code>
should print <code>some module!</code>.</p>
</section><section><h3>Source map v3 support<span><a class="mark" href="#source-map-v3-support" id="source-map-v3-support">#</a></span><a aria-hidden="true" class="legacy" id="module_source_map_v3_support"></a></h3>
<div class="api_metadata">
<span>Added in: v13.7.0, v12.17.0</span>
</div>
<p></p><div class="api_stability api_stability_1"><a href="documentation.html#stability-index">Stability: 1</a> - Experimental</div><p></p>
<p>Helpers for interacting with the source map cache. This cache is
populated when source map parsing is enabled and
<a href="https://sourcemaps.info/spec.html#h.lmz475t4mvbx">source map include directives</a> are found in a modules' footer.</p>
<p>To enable source map parsing, Node.js must be run with the flag
<a href="cli.html#--enable-source-maps"><code>--enable-source-maps</code></a>, or with code coverage enabled by setting
<a href="cli.html#node_v8_coveragedir"><code>NODE_V8_COVERAGE=dir</code></a>.</p>
<pre class="with-26-chars"><input class="js-flavor-toggle" type="checkbox" checked aria-label="Show modern ES modules syntax"><code class="language-js mjs"><span class="hljs-comment">// module.mjs</span>
<span class="hljs-comment">// In an ECMAScript module</span>
<span class="hljs-keyword">import</span> { findSourceMap, <span class="hljs-title class_">SourceMap</span> } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:module'</span>;</code><code class="language-js cjs"><span class="hljs-comment">// module.cjs</span>
<span class="hljs-comment">// In a CommonJS module</span>
<span class="hljs-keyword">const</span> { findSourceMap, <span class="hljs-title class_">SourceMap</span> } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'node:module'</span>);</code><button class="copy-button">copy</button></pre>
<!-- Anchors to make sure old links find a target -->
<p><a id="module_module_findsourcemap_path_error"></a></p>
<h4><code>module.findSourceMap(path)</code><span><a class="mark" href="#modulefindsourcemappath" id="modulefindsourcemappath">#</a></span><a aria-hidden="true" class="legacy" id="module_module_findsourcemap_path"></a></h4>
<div class="api_metadata">
<span>Added in: v13.7.0, v12.17.0</span>
</div>
<ul>
<li><code>path</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li>
<li>Returns: <a href="module.html#class-modulesourcemap" class="type"><module.SourceMap></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type"><undefined></a> Returns <code>module.SourceMap</code> if a source
map is found, <code>undefined</code> otherwise.</li>
</ul>
<p><code>path</code> is the resolved path for the file for which a corresponding source map
should be fetched.</p>
<h4>Class: <code>module.SourceMap</code><span><a class="mark" href="#class-modulesourcemap" id="class-modulesourcemap">#</a></span><a aria-hidden="true" class="legacy" id="module_class_module_sourcemap"></a></h4>
<div class="api_metadata">
<span>Added in: v13.7.0, v12.17.0</span>
</div>
<h5><code>new SourceMap(payload[, { lineLengths }])</code><span><a class="mark" href="#new-sourcemappayload--linelengths-" id="new-sourcemappayload--linelengths-">#</a></span><a aria-hidden="true" class="legacy" id="module_new_sourcemap_payload_linelengths"></a></h5>
<ul>
<li><code>payload</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li>
<li><code>lineLengths</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number[]></a></li>
</ul>
<p>Creates a new <code>sourceMap</code> instance.</p>
<p><code>payload</code> is an object with keys matching the <a href="https://sourcemaps.info/spec.html#h.mofvlxcwqzej">Source map v3 format</a>:</p>
<ul>
<li><code>file</code>: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li>
<li><code>version</code>: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li>
<li><code>sources</code>: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string[]></a></li>
<li><code>sourcesContent</code>: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string[]></a></li>
<li><code>names</code>: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string[]></a></li>
<li><code>mappings</code>: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li>
<li><code>sourceRoot</code>: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li>
</ul>
<p><code>lineLengths</code> is an optional array of the length of each line in the
generated code.</p>
<h5><code>sourceMap.payload</code><span><a class="mark" href="#sourcemappayload" id="sourcemappayload">#</a></span><a aria-hidden="true" class="legacy" id="module_sourcemap_payload"></a></h5>
<ul>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li>
</ul>
<p>Getter for the payload used to construct the <a href="#class-modulesourcemap"><code>SourceMap</code></a> instance.</p>
<h5><code>sourceMap.findEntry(lineOffset, columnOffset)</code><span><a class="mark" href="#sourcemapfindentrylineoffset-columnoffset" id="sourcemapfindentrylineoffset-columnoffset">#</a></span><a aria-hidden="true" class="legacy" id="module_sourcemap_findentry_lineoffset_columnoffset"></a></h5>
<ul>
<li><code>lineOffset</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> The zero-indexed line number offset in
the generated source</li>
<li><code>columnOffset</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> The zero-indexed column number offset
in the generated source</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li>
</ul>
<p>Given a line offset and column offset in the generated source
file, returns an object representing the SourceMap range in the
original file if found, or an empty object if not.</p>
<p>The object returned contains the following keys:</p>
<ul>
<li>generatedLine: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> The line offset of the start of the
range in the generated source</li>
<li>generatedColumn: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> The column offset of start of the
range in the generated source</li>
<li>originalSource: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> The file name of the original source,
as reported in the SourceMap</li>
<li>originalLine: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> The line offset of the start of the
range in the original source</li>
<li>originalColumn: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> The column offset of start of the
range in the original source</li>
<li>name: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li>
</ul>
<p>The returned value represents the raw range as it appears in the
SourceMap, based on zero-indexed offsets, <em>not</em> 1-indexed line and
column numbers as they appear in Error messages and CallSite
objects.</p>
<p>To get the corresponding 1-indexed line and column numbers from a
lineNumber and columnNumber as they are reported by Error stacks
and CallSite objects, use <code>sourceMap.findOrigin(lineNumber, columnNumber)</code></p>
<h5><code>sourceMap.findOrigin(lineNumber, columnNumber)</code><span><a class="mark" href="#sourcemapfindoriginlinenumber-columnnumber" id="sourcemapfindoriginlinenumber-columnnumber">#</a></span><a aria-hidden="true" class="legacy" id="module_sourcemap_findorigin_linenumber_columnnumber"></a></h5>
<ul>
<li><code>lineNumber</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> The 1-indexed line number of the call
site in the generated source</li>
<li><code>columnNumber</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> The 1-indexed column number
of the call site in the generated source</li>
<li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li>
</ul>
<p>Given a 1-indexed <code>lineNumber</code> and <code>columnNumber</code> from a call site in
the generated source, find the corresponding call site location
in the original source.</p>
<p>If the <code>lineNumber</code> and <code>columnNumber</code> provided are not found in any
source map, then an empty object is returned. Otherwise, the
returned object contains the following keys:</p>
<ul>
<li>name: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Undefined_type" class="type"><undefined></a> The name of the range in the
source map, if one was provided</li>
<li>fileName: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> The file name of the original source, as
reported in the SourceMap</li>
<li>lineNumber: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> The 1-indexed lineNumber of the
corresponding call site in the original source</li>
<li>columnNumber: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> The 1-indexed columnNumber of the
corresponding call site in the original source</li>
</ul></section>
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