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<!DOCTYPE html> <html lang="en"> <head> <meta charset="utf-8"> <meta name="viewport" content="width=device-width"> <meta name="nodejs.org:node-version" content="v22.22.0"> <title>Modules: ECMAScript modules | Node.js v22.22.0 Documentation</title> <link rel="stylesheet" href="https://fonts.googleapis.com/css?family=Lato:400,700,400italic&display=fallback"> <link rel="stylesheet" href="assets/style.css"> <link rel="stylesheet" href="assets/hljs.css"> <link rel="canonical" href="https://nodejs.org/api/esm.html"> <script async defer src="assets/api.js" type="text/javascript"></script> <script> const storedTheme = localStorage.getItem('theme'); // Follow operating system theme preference if (storedTheme === null && window.matchMedia) { const mq = window.matchMedia('(prefers-color-scheme: dark)'); if (mq.matches) { document.documentElement.classList.add('dark-mode'); } } else if (storedTheme === 'dark') { document.documentElement.classList.add('dark-mode'); } </script> </head> <body 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</div> <div id="column1" data-id="esm" class="interior"> <header class="header"> <div class="header-container"> <h1>Node.js v22.22.0 documentation</h1> <button class="theme-toggle-btn" id="theme-toggle-btn" title="Toggle dark mode/light mode" aria-label="Toggle dark mode/light mode" hidden> <svg xmlns="http://www.w3.org/2000/svg" class="icon dark-icon" height="24" width="24"> <path fill="none" d="M0 0h24v24H0z" /> <path d="M11.1 12.08c-2.33-4.51-.5-8.48.53-10.07C6.27 2.2 1.98 6.59 1.98 12c0 .14.02.28.02.42.62-.27 1.29-.42 2-.42 1.66 0 3.18.83 4.1 2.15A4.01 4.01 0 0111 18c0 1.52-.87 2.83-2.12 3.51.98.32 2.03.5 3.11.5 3.5 0 6.58-1.8 8.37-4.52-2.36.23-6.98-.97-9.26-5.41z"/> <path d="M7 16h-.18C6.4 14.84 5.3 14 4 14c-1.66 0-3 1.34-3 3s1.34 3 3 3h3c1.1 0 2-.9 2-2s-.9-2-2-2z"/> </svg> <svg xmlns="http://www.w3.org/2000/svg" class="icon light-icon" height="24" width="24"> <path d="M0 0h24v24H0z" fill="none" /> <path d="M6.76 4.84l-1.8-1.79-1.41 1.41 1.79 1.79 1.42-1.41zM4 10.5H1v2h3v-2zm9-9.95h-2V3.5h2V.55zm7.45 3.91l-1.41-1.41-1.79 1.79 1.41 1.41 1.79-1.79zm-3.21 13.7l1.79 1.8 1.41-1.41-1.8-1.79-1.4 1.4zM20 10.5v2h3v-2h-3zm-8-5c-3.31 0-6 2.69-6 6s2.69 6 6 6 6-2.69 6-6-2.69-6-6-6zm-1 16.95h2V19.5h-2v2.95zm-7.45-3.91l1.41 1.41 1.79-1.8-1.41-1.41-1.79 1.8z"/> </svg> </button> </div> <div id="gtoc"> <ul> <li class="pinned-header">Node.js v22.22.0</li> <li class="picker-header"> <a href="#toc-picker" aria-controls="toc-picker"> <span class="picker-arrow"></span> Table of contents </a> <div class="picker" tabindex="-1"><div class="toc"><ul id="toc-picker"> <li><a href="#modules-ecmascript-modules">Modules: ECMAScript modules</a> <ul> <li><a href="#introduction">Introduction</a></li> <li><a href="#enabling">Enabling</a></li> <li><a href="#packages">Packages</a></li> <li><a href="#import-specifiers"><code>import</code> Specifiers</a> <ul> <li><a href="#terminology">Terminology</a></li> <li><a href="#mandatory-file-extensions">Mandatory file extensions</a></li> <li><a href="#urls">URLs</a> <ul> <li><a href="#file-urls"><code>file:</code> URLs</a></li> <li><a href="#data-imports"><code>data:</code> imports</a></li> <li><a href="#node-imports"><code>node:</code> imports</a></li> </ul> </li> </ul> </li> <li><a href="#import-attributes">Import attributes</a></li> <li><a href="#built-in-modules">Built-in modules</a></li> <li><a href="#import-expressions"><code>import()</code> expressions</a></li> <li><a href="#importmeta"><code>import.meta</code></a> <ul> <li><a href="#importmetadirname"><code>import.meta.dirname</code></a></li> <li><a href="#importmetafilename"><code>import.meta.filename</code></a></li> <li><a href="#importmetaurl"><code>import.meta.url</code></a></li> <li><span class="stability_1.0"><a href="#importmetamain"><code>import.meta.main</code></a></span></li> <li><span class="stability_1.2"><a href="#importmetaresolvespecifier"><code>import.meta.resolve(specifier)</code></a></span></li> </ul> </li> <li><a href="#interoperability-with-commonjs">Interoperability with CommonJS</a> <ul> <li><a href="#import-statements"><code>import</code> statements</a></li> <li><a href="#require"><code>require</code></a></li> <li><a href="#commonjs-namespaces">CommonJS Namespaces</a></li> <li><a href="#differences-between-es-modules-and-commonjs">Differences between ES modules and CommonJS</a> <ul> <li><a href="#no-require-exports-or-moduleexports">No <code>require</code>, <code>exports</code>, or <code>module.exports</code></a></li> <li><a href="#no-__filename-or-__dirname">No <code>__filename</code> or <code>__dirname</code></a></li> <li><a href="#no-addon-loading">No Addon Loading</a></li> <li><a href="#no-requiremain">No <code>require.main</code></a></li> <li><a href="#no-requireresolve">No <code>require.resolve</code></a></li> <li><a href="#no-node_path">No <code>NODE_PATH</code></a></li> <li><a href="#no-requireextensions">No <code>require.extensions</code></a></li> <li><a href="#no-requirecache">No <code>require.cache</code></a></li> </ul> </li> </ul> </li> <li><a href="#json-modules">JSON modules</a></li> <li><a href="#wasm-modules">Wasm modules</a></li> <li><span class="stability_1"><a href="#wasm-modules_1">Wasm modules</a></span> <ul> <li><a href="#javascript-string-builtins">JavaScript String Builtins</a></li> <li><a href="#reserved-wasm-namespaces">Reserved Wasm Namespaces</a></li> </ul> </li> <li><a href="#top-level-await">Top-level <code>await</code></a></li> <li><a href="#loaders">Loaders</a></li> <li><a href="#resolution-and-loading-algorithm">Resolution and loading algorithm</a> <ul> <li><a href="#features">Features</a></li> <li><a href="#resolution-algorithm">Resolution algorithm</a></li> <li><a href="#resolution-algorithm-specification">Resolution Algorithm Specification</a></li> <li><a href="#customizing-esm-specifier-resolution-algorithm">Customizing ESM specifier resolution algorithm</a></li> </ul> </li> </ul> </li> </ul></div></div> </li> <li class="picker-header"> <a href="#gtoc-picker" aria-controls="gtoc-picker"> <span class="picker-arrow"></span> Index </a> <div class="picker" tabindex="-1" id="gtoc-picker"><ul> <li><a href="documentation.html" class="nav-documentation">About this documentation</a></li> <li><a href="synopsis.html" class="nav-synopsis">Usage and example</a></li> <li> <a href="index.html">Index</a> </li> </ul> <hr class="line"> <ul> <li><a href="assert.html" class="nav-assert">Assertion testing</a></li> <li><a href="async_context.html" class="nav-async_context">Asynchronous context tracking</a></li> <li><a href="async_hooks.html" class="nav-async_hooks">Async hooks</a></li> <li><a href="buffer.html" class="nav-buffer">Buffer</a></li> <li><a href="addons.html" class="nav-addons">C++ addons</a></li> <li><a href="n-api.html" class="nav-n-api">C/C++ addons with Node-API</a></li> <li><a href="embedding.html" class="nav-embedding">C++ embedder API</a></li> <li><a href="child_process.html" class="nav-child_process">Child processes</a></li> <li><a href="cluster.html" class="nav-cluster">Cluster</a></li> <li><a href="cli.html" class="nav-cli">Command-line options</a></li> <li><a href="console.html" class="nav-console">Console</a></li> <li><a href="crypto.html" class="nav-crypto">Crypto</a></li> <li><a href="debugger.html" class="nav-debugger">Debugger</a></li> <li><a href="deprecations.html" class="nav-deprecations">Deprecated APIs</a></li> <li><a href="diagnostics_channel.html" class="nav-diagnostics_channel">Diagnostics Channel</a></li> <li><a href="dns.html" class="nav-dns">DNS</a></li> <li><a href="domain.html" class="nav-domain">Domain</a></li> <li><a href="environment_variables.html" class="nav-environment_variables">Environment Variables</a></li> <li><a href="errors.html" class="nav-errors">Errors</a></li> <li><a href="events.html" class="nav-events">Events</a></li> <li><a href="fs.html" class="nav-fs">File system</a></li> <li><a href="globals.html" 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href="tracing.html" class="nav-tracing">Trace events</a></li> <li><a href="tty.html" class="nav-tty">TTY</a></li> <li><a href="dgram.html" class="nav-dgram">UDP/datagram</a></li> <li><a href="url.html" class="nav-url">URL</a></li> <li><a href="util.html" class="nav-util">Utilities</a></li> <li><a href="v8.html" class="nav-v8">V8</a></li> <li><a href="vm.html" class="nav-vm">VM</a></li> <li><a href="wasi.html" class="nav-wasi">WASI</a></li> <li><a href="webcrypto.html" class="nav-webcrypto">Web Crypto API</a></li> <li><a href="webstreams.html" class="nav-webstreams">Web Streams API</a></li> <li><a href="worker_threads.html" class="nav-worker_threads">Worker threads</a></li> <li><a href="zlib.html" class="nav-zlib">Zlib</a></li> </ul> <hr class="line"> <ul> <li><a href="https://github.com/nodejs/node" class="nav-https-github-com-nodejs-node">Code repository and issue tracker</a></li> </ul></div> </li> <li class="picker-header"> <a href="#alt-docs" aria-controls="alt-docs"> <span class="picker-arrow"></span> Other versions </a> <div class="picker" tabindex="-1"><ol id="alt-docs"><li><a href="https://nodejs.org/docs/latest-v25.x/api/esm.html">25.x</a></li> <li><a href="https://nodejs.org/docs/latest-v24.x/api/esm.html">24.x <b>LTS</b></a></li> <li><a href="https://nodejs.org/docs/latest-v23.x/api/esm.html">23.x</a></li> <li><a href="https://nodejs.org/docs/latest-v22.x/api/esm.html">22.x <b>LTS</b></a></li> <li><a href="https://nodejs.org/docs/latest-v21.x/api/esm.html">21.x</a></li> <li><a href="https://nodejs.org/docs/latest-v20.x/api/esm.html">20.x <b>LTS</b></a></li> <li><a href="https://nodejs.org/docs/latest-v19.x/api/esm.html">19.x</a></li> <li><a href="https://nodejs.org/docs/latest-v18.x/api/esm.html">18.x</a></li> <li><a href="https://nodejs.org/docs/latest-v17.x/api/esm.html">17.x</a></li> <li><a href="https://nodejs.org/docs/latest-v16.x/api/esm.html">16.x</a></li> <li><a href="https://nodejs.org/docs/latest-v15.x/api/esm.html">15.x</a></li> <li><a href="https://nodejs.org/docs/latest-v14.x/api/esm.html">14.x</a></li> <li><a href="https://nodejs.org/docs/latest-v13.x/api/esm.html">13.x</a></li> <li><a href="https://nodejs.org/docs/latest-v12.x/api/esm.html">12.x</a></li> <li><a href="https://nodejs.org/docs/latest-v11.x/api/esm.html">11.x</a></li> <li><a href="https://nodejs.org/docs/latest-v10.x/api/esm.html">10.x</a></li> <li><a href="https://nodejs.org/docs/latest-v9.x/api/esm.html">9.x</a></li> <li><a href="https://nodejs.org/docs/latest-v8.x/api/esm.html">8.x</a></li></ol></div> </li> <li class="picker-header"> <a href="#options-picker" aria-controls="options-picker"> <span class="picker-arrow"></span> Options </a> <div class="picker" tabindex="-1"> <ul id="options-picker"> <li> <a href="all.html">View on single page</a> </li> <li> <a href="esm.json">View as JSON</a> </li> <li class="edit_on_github"><a href="https://github.com/nodejs/node/edit/main/doc/api/esm.md">Edit on GitHub</a></li> </ul> </div> </li> </ul> </div> <hr> </header> <details role="navigation" id="toc" open><summary>Table of contents</summary><ul> <li><a href="#modules-ecmascript-modules">Modules: ECMAScript modules</a> <ul> <li><a href="#introduction">Introduction</a></li> <li><a href="#enabling">Enabling</a></li> <li><a href="#packages">Packages</a></li> <li><a href="#import-specifiers"><code>import</code> Specifiers</a> <ul> <li><a href="#terminology">Terminology</a></li> <li><a href="#mandatory-file-extensions">Mandatory file extensions</a></li> <li><a href="#urls">URLs</a> <ul> <li><a href="#file-urls"><code>file:</code> URLs</a></li> <li><a href="#data-imports"><code>data:</code> imports</a></li> <li><a href="#node-imports"><code>node:</code> imports</a></li> </ul> </li> </ul> </li> <li><a href="#import-attributes">Import attributes</a></li> <li><a href="#built-in-modules">Built-in modules</a></li> <li><a href="#import-expressions"><code>import()</code> expressions</a></li> <li><a href="#importmeta"><code>import.meta</code></a> <ul> <li><a href="#importmetadirname"><code>import.meta.dirname</code></a></li> <li><a href="#importmetafilename"><code>import.meta.filename</code></a></li> <li><a href="#importmetaurl"><code>import.meta.url</code></a></li> <li><span class="stability_1.0"><a href="#importmetamain"><code>import.meta.main</code></a></span></li> <li><span class="stability_1.2"><a href="#importmetaresolvespecifier"><code>import.meta.resolve(specifier)</code></a></span></li> </ul> </li> <li><a href="#interoperability-with-commonjs">Interoperability with CommonJS</a> <ul> <li><a href="#import-statements"><code>import</code> statements</a></li> <li><a href="#require"><code>require</code></a></li> <li><a href="#commonjs-namespaces">CommonJS Namespaces</a></li> <li><a href="#differences-between-es-modules-and-commonjs">Differences between ES modules and CommonJS</a> <ul> <li><a href="#no-require-exports-or-moduleexports">No <code>require</code>, <code>exports</code>, or <code>module.exports</code></a></li> <li><a href="#no-__filename-or-__dirname">No <code>__filename</code> or <code>__dirname</code></a></li> <li><a href="#no-addon-loading">No Addon Loading</a></li> <li><a href="#no-requiremain">No <code>require.main</code></a></li> <li><a href="#no-requireresolve">No <code>require.resolve</code></a></li> <li><a href="#no-node_path">No <code>NODE_PATH</code></a></li> <li><a href="#no-requireextensions">No <code>require.extensions</code></a></li> <li><a href="#no-requirecache">No <code>require.cache</code></a></li> </ul> </li> </ul> </li> <li><a href="#json-modules">JSON modules</a></li> <li><a href="#wasm-modules">Wasm modules</a></li> <li><span class="stability_1"><a href="#wasm-modules_1">Wasm modules</a></span> <ul> <li><a href="#javascript-string-builtins">JavaScript String Builtins</a></li> <li><a href="#reserved-wasm-namespaces">Reserved Wasm Namespaces</a></li> </ul> </li> <li><a href="#top-level-await">Top-level <code>await</code></a></li> <li><a href="#loaders">Loaders</a></li> <li><a href="#resolution-and-loading-algorithm">Resolution and loading algorithm</a> <ul> <li><a href="#features">Features</a></li> <li><a href="#resolution-algorithm">Resolution algorithm</a></li> <li><a href="#resolution-algorithm-specification">Resolution Algorithm Specification</a></li> <li><a href="#customizing-esm-specifier-resolution-algorithm">Customizing ESM specifier resolution algorithm</a></li> </ul> </li> </ul> </li> </ul></details> <div role="main" id="apicontent"> <h2>Modules: ECMAScript modules<span><a class="mark" href="#modules-ecmascript-modules" id="modules-ecmascript-modules">#</a></span><a aria-hidden="true" class="legacy" id="esm_modules_ecmascript_modules"></a></h2> <div class="api_metadata"> <details class="changelog"><summary>History</summary> <table> <tbody><tr><th>Version</th><th>Changes</th></tr> <tr><td>v22.12.0</td> <td><p>Import attributes are no longer experimental.</p></td></tr> <tr><td>v22.0.0</td> <td><p>Drop support for import assertions.</p></td></tr> <tr><td>v21.0.0, v20.10.0, v18.20.0</td> <td><p>Add experimental support for import attributes.</p></td></tr> <tr><td>v20.0.0, v18.19.0</td> <td><p>Module customization hooks are executed off the main thread.</p></td></tr> <tr><td>v18.6.0, v16.17.0</td> <td><p>Add support for chaining module customization hooks.</p></td></tr> <tr><td>v17.1.0, v16.14.0</td> <td><p>Add experimental support for import assertions.</p></td></tr> <tr><td>v17.0.0, v16.12.0</td> <td><p>Consolidate customization hooks, removed <code>getFormat</code>, <code>getSource</code>, <code>transformSource</code>, and <code>getGlobalPreloadCode</code> hooks added <code>load</code> and <code>globalPreload</code> hooks allowed returning <code>format</code> from either <code>resolve</code> or <code>load</code> hooks.</p></td></tr> <tr><td>v14.8.0</td> <td><p>Unflag Top-Level Await.</p></td></tr> <tr><td>v15.3.0, v14.17.0, v12.22.0</td> <td><p>Stabilize modules implementation.</p></td></tr> <tr><td>v14.13.0, v12.20.0</td> <td><p>Support for detection of CommonJS named exports.</p></td></tr> <tr><td>v14.0.0, v13.14.0, v12.20.0</td> <td><p>Remove experimental modules warning.</p></td></tr> <tr><td>v13.2.0, v12.17.0</td> <td><p>Loading ECMAScript modules no longer requires a command-line flag.</p></td></tr> <tr><td>v12.0.0</td> <td><p>Add support for ES modules using <code>.js</code> file extension via <code>package.json</code> <code>"type"</code> field.</p></td></tr> <tr><td>v8.5.0</td> <td><p><span>Added in: v8.5.0</span></p></td></tr> </tbody></table> </details> </div> <p></p><div class="api_stability api_stability_2"><a href="documentation.html#stability-index">Stability: 2</a> - Stable</div><p></p> <section><h3>Introduction<span><a class="mark" href="#introduction" id="introduction">#</a></span><a aria-hidden="true" class="legacy" id="esm_introduction"></a></h3> <p>ECMAScript modules are <a href="https://tc39.github.io/ecma262/#sec-modules">the official standard format</a> to package JavaScript code for reuse. Modules are defined using a variety of <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/import"><code>import</code></a> and <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/export"><code>export</code></a> statements.</p> <p>The following example of an ES module exports a function:</p> <pre><code class="language-js"><span class="hljs-comment">// addTwo.mjs</span> <span class="hljs-keyword">function</span> <span class="hljs-title function_">addTwo</span>(<span class="hljs-params">num</span>) { <span class="hljs-keyword">return</span> num + <span class="hljs-number">2</span>; } <span class="hljs-keyword">export</span> { addTwo };</code> <button class="copy-button">copy</button></pre> <p>The following example of an ES module imports the function from <code>addTwo.mjs</code>:</p> <pre><code class="language-js"><span class="hljs-comment">// app.mjs</span> <span class="hljs-keyword">import</span> { addTwo } <span class="hljs-keyword">from</span> <span class="hljs-string">'./addTwo.mjs'</span>; <span class="hljs-comment">// Prints: 6</span> <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-title function_">addTwo</span>(<span class="hljs-number">4</span>));</code> <button class="copy-button">copy</button></pre> <p>Node.js fully supports ECMAScript modules as they are currently specified and provides interoperability between them and its original module format, <a href="modules.html">CommonJS</a>.</p> <!-- Anchors to make sure old links find a target --> <p><i id="esm_package_json_type_field"></i><i id="esm_package_scope_and_file_extensions"></i><i id="esm_input_type_flag"></i></p> </section><section><h3>Enabling<span><a class="mark" href="#enabling" id="enabling">#</a></span><a aria-hidden="true" class="legacy" id="esm_enabling"></a></h3> <p>Node.js has two module systems: <a href="modules.html">CommonJS</a> modules and ECMAScript modules.</p> <p>Authors can tell Node.js to interpret JavaScript as an ES module via the <code>.mjs</code> file extension, the <code>package.json</code> <a href="packages.html#type"><code>"type"</code></a> field with a value <code>"module"</code>, the <a href="cli.html#--input-typetype"><code>--input-type</code></a> flag with a value of <code>"module"</code>, or the <a href="cli.html#--experimental-default-typetype"><code>--experimental-default-type</code></a> flag with a value of <code>"module"</code>. These are explicit markers of code being intended to run as an ES module.</p> <p>Inversely, authors can tell Node.js to interpret JavaScript as CommonJS via the <code>.cjs</code> file extension, the <code>package.json</code> <a href="packages.html#type"><code>"type"</code></a> field with a value <code>"commonjs"</code>, the <a href="cli.html#--input-typetype"><code>--input-type</code></a> flag with a value of <code>"commonjs"</code>, or the <a href="cli.html#--experimental-default-typetype"><code>--experimental-default-type</code></a> flag with a value of <code>"commonjs"</code>.</p> <p>When code lacks explicit markers for either module system, Node.js will inspect the source code of a module to look for ES module syntax. If such syntax is found, Node.js will run the code as an ES module; otherwise it will run the module as CommonJS. See <a href="packages.html#determining-module-system">Determining module system</a> for more details.</p> <!-- Anchors to make sure old links find a target --> <p><i id="esm_package_entry_points"></i><i id="esm_main_entry_point_export"></i><i id="esm_subpath_exports"></i><i id="esm_package_exports_fallbacks"></i><i id="esm_exports_sugar"></i><i id="esm_conditional_exports"></i><i id="esm_nested_conditions"></i><i id="esm_self_referencing_a_package_using_its_name"></i><i id="esm_internal_package_imports"></i><i id="esm_dual_commonjs_es_module_packages"></i><i id="esm_dual_package_hazard"></i><i id="esm_writing_dual_packages_while_avoiding_or_minimizing_hazards"></i><i id="esm_approach_1_use_an_es_module_wrapper"></i><i id="esm_approach_2_isolate_state"></i></p> </section><section><h3>Packages<span><a class="mark" href="#packages" id="packages">#</a></span><a aria-hidden="true" class="legacy" id="esm_packages"></a></h3> <p>This section was moved to <a href="packages.html">Modules: Packages</a>.</p> </section><section><h3><code>import</code> Specifiers<span><a class="mark" href="#import-specifiers" id="import-specifiers">#</a></span><a aria-hidden="true" class="legacy" id="esm_import_specifiers"></a></h3> <div> <h4>Terminology<span><a class="mark" href="#terminology" id="terminology">#</a></span><a aria-hidden="true" class="legacy" id="esm_terminology"></a></h4> <p>The <em>specifier</em> of an <code>import</code> statement is the string after the <code>from</code> keyword, e.g. <code>'node:path'</code> in <code>import { sep } from 'node:path'</code>. Specifiers are also used in <code>export from</code> statements, and as the argument to an <code>import()</code> expression.</p> <p>There are three types of specifiers:</p> <ul> <li> <p><em>Relative specifiers</em> like <code>'./startup.js'</code> or <code>'../config.mjs'</code>. They refer to a path relative to the location of the importing file. <em>The file extension is always necessary for these.</em></p> </li> <li> <p><em>Bare specifiers</em> like <code>'some-package'</code> or <code>'some-package/shuffle'</code>. They can refer to the main entry point of a package by the package name, or a specific feature module within a package prefixed by the package name as per the examples respectively. <em>Including the file extension is only necessary for packages without an <a href="packages.html#exports"><code>"exports"</code></a> field.</em></p> </li> <li> <p><em>Absolute specifiers</em> like <code>'file:///opt/nodejs/config.js'</code>. They refer directly and explicitly to a full path.</p> </li> </ul> <p>Bare specifier resolutions are handled by the <a href="#resolution-algorithm-specification">Node.js module resolution and loading algorithm</a>. All other specifier resolutions are always only resolved with the standard relative <a href="https://url.spec.whatwg.org/">URL</a> resolution semantics.</p> <p>Like in CommonJS, module files within packages can be accessed by appending a path to the package name unless the package's <a href="packages.html#nodejs-packagejson-field-definitions"><code>package.json</code></a> contains an <a href="packages.html#exports"><code>"exports"</code></a> field, in which case files within packages can only be accessed via the paths defined in <a href="packages.html#exports"><code>"exports"</code></a>.</p> <p>For details on these package resolution rules that apply to bare specifiers in the Node.js module resolution, see the <a href="packages.html">packages documentation</a>.</p> </div><div> <h4>Mandatory file extensions<span><a class="mark" href="#mandatory-file-extensions" id="mandatory-file-extensions">#</a></span><a aria-hidden="true" class="legacy" id="esm_mandatory_file_extensions"></a></h4> <p>A file extension must be provided when using the <code>import</code> keyword to resolve relative or absolute specifiers. Directory indexes (e.g. <code>'./startup/index.js'</code>) must also be fully specified.</p> <p>This behavior matches how <code>import</code> behaves in browser environments, assuming a typically configured server.</p> </div><div> <h4>URLs<span><a class="mark" href="#urls" id="urls">#</a></span><a aria-hidden="true" class="legacy" id="esm_urls"></a></h4> <p>ES modules are resolved and cached as URLs. This means that special characters must be <a href="url.html#percent-encoding-in-urls">percent-encoded</a>, such as <code>#</code> with <code>%23</code> and <code>?</code> with <code>%3F</code>.</p> <p><code>file:</code>, <code>node:</code>, and <code>data:</code> URL schemes are supported. A specifier like <code>'https://example.com/app.js'</code> is not supported natively in Node.js unless using a <a href="module.html#import-from-https">custom HTTPS loader</a>.</p> <div> <h5><code>file:</code> URLs<span><a class="mark" href="#file-urls" id="file-urls">#</a></span><a aria-hidden="true" class="legacy" id="esm_file_urls"></a></h5> <p>Modules are loaded multiple times if the <code>import</code> specifier used to resolve them has a different query or fragment.</p> <pre><code class="language-js"><span class="hljs-keyword">import</span> <span class="hljs-string">'./foo.mjs?query=1'</span>; <span class="hljs-comment">// loads ./foo.mjs with query of "?query=1"</span> <span class="hljs-keyword">import</span> <span class="hljs-string">'./foo.mjs?query=2'</span>; <span class="hljs-comment">// loads ./foo.mjs with query of "?query=2"</span></code> <button class="copy-button">copy</button></pre> <p>The volume root may be referenced via <code>/</code>, <code>//</code>, or <code>file:///</code>. Given the differences between <a href="https://url.spec.whatwg.org/">URL</a> and path resolution (such as percent encoding details), it is recommended to use <a href="url.html#urlpathtofileurlpath-options">url.pathToFileURL</a> when importing a path.</p> </div><div> <h5><code>data:</code> imports<span><a class="mark" href="#data-imports" id="data-imports">#</a></span><a aria-hidden="true" class="legacy" id="esm_data_imports"></a></h5> <div class="api_metadata"> <span>Added in: v12.10.0</span> </div> <p><a href="https://developer.mozilla.org/en-US/docs/Web/HTTP/Basics_of_HTTP/Data_URIs"><code>data:</code> URLs</a> are supported for importing with the following MIME types:</p> <ul> <li><code>text/javascript</code> for ES modules</li> <li><code>application/json</code> for JSON</li> <li><code>application/wasm</code> for Wasm</li> </ul> <pre><code class="language-js"><span class="hljs-keyword">import</span> <span class="hljs-string">'data:text/javascript,console.log("hello!");'</span>; <span class="hljs-keyword">import</span> _ <span class="hljs-keyword">from</span> <span class="hljs-string">'data:application/json,"world!"'</span> <span class="hljs-keyword">with</span> { <span class="hljs-attr">type</span>: <span class="hljs-string">'json'</span> };</code> <button class="copy-button">copy</button></pre> <p><code>data:</code> URLs only resolve <a href="#terminology">bare specifiers</a> for builtin modules and <a href="#terminology">absolute specifiers</a>. Resolving <a href="#terminology">relative specifiers</a> does not work because <code>data:</code> is not a <a href="https://url.spec.whatwg.org/#special-scheme">special scheme</a>. For example, attempting to load <code>./foo</code> from <code>data:text/javascript,import "./foo";</code> fails to resolve because there is no concept of relative resolution for <code>data:</code> URLs.</p> </div><div> <h5><code>node:</code> imports<span><a class="mark" href="#node-imports" id="node-imports">#</a></span><a aria-hidden="true" class="legacy" id="esm_node_imports"></a></h5> <div class="api_metadata"> <details class="changelog"><summary>History</summary> <table> <tbody><tr><th>Version</th><th>Changes</th></tr> <tr><td>v16.0.0, v14.18.0</td> <td><p>Added <code>node:</code> import support to <code>require(...)</code>.</p></td></tr> <tr><td>v14.13.1, v12.20.0</td> <td><p><span>Added in: v14.13.1, v12.20.0</span></p></td></tr> </tbody></table> </details> </div> <p><code>node:</code> URLs are supported as an alternative means to load Node.js builtin modules. This URL scheme allows for builtin modules to be referenced by valid absolute URL strings.</p> <pre><code class="language-js"><span class="hljs-keyword">import</span> fs <span class="hljs-keyword">from</span> <span class="hljs-string">'node:fs/promises'</span>;</code> <button class="copy-button">copy</button></pre> <p><a id="import-assertions"></a></p> </div></div> </section><section><h3>Import attributes<span><a class="mark" href="#import-attributes" id="import-attributes">#</a></span><a aria-hidden="true" class="legacy" id="esm_import_attributes"></a></h3> <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, v18.20.0</td> <td><p>Switch from Import Assertions to Import Attributes.</p></td></tr> <tr><td>v17.1.0, v16.14.0</td> <td><p><span>Added in: v17.1.0, v16.14.0</span></p></td></tr> </tbody></table> </details> </div> <p><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/import/with">Import attributes</a> are an inline syntax for module import statements to pass on more information alongside the module specifier.</p> <pre><code class="language-js"><span class="hljs-keyword">import</span> fooData <span class="hljs-keyword">from</span> <span class="hljs-string">'./foo.json'</span> <span class="hljs-keyword">with</span> { <span class="hljs-attr">type</span>: <span class="hljs-string">'json'</span> }; <span class="hljs-keyword">const</span> { <span class="hljs-attr">default</span>: barData } = <span class="hljs-keyword">await</span> <span class="hljs-keyword">import</span>(<span class="hljs-string">'./bar.json'</span>, { <span class="hljs-attr">with</span>: { <span class="hljs-attr">type</span>: <span class="hljs-string">'json'</span> } });</code> <button class="copy-button">copy</button></pre> <p>Node.js only supports the <code>type</code> attribute, for which it supports the following values:</p> <table><thead><tr><th>Attribute <code>type</code></th><th>Needed for</th></tr></thead><tbody><tr><td><code>'json'</code></td><td><a href="#json-modules">JSON modules</a></td></tr></tbody></table> <p>The <code>type: 'json'</code> attribute is mandatory when importing JSON modules.</p> </section><section><h3>Built-in modules<span><a class="mark" href="#built-in-modules" id="built-in-modules">#</a></span><a aria-hidden="true" class="legacy" id="esm_built_in_modules"></a></h3> <p><a href="modules.html#built-in-modules">Built-in modules</a> provide named exports of their public API. A default export is also provided which is the value of the CommonJS exports. The default export can be used for, among other things, modifying the named exports. Named exports of built-in modules are updated only by calling <a href="module.html#modulesyncbuiltinesmexports"><code>module.syncBuiltinESMExports()</code></a>.</p> <pre><code class="language-js"><span class="hljs-keyword">import</span> <span class="hljs-title class_">EventEmitter</span> <span class="hljs-keyword">from</span> <span class="hljs-string">'node:events'</span>; <span class="hljs-keyword">const</span> e = <span class="hljs-keyword">new</span> <span class="hljs-title class_">EventEmitter</span>();</code> <button class="copy-button">copy</button></pre> <pre><code class="language-js"><span class="hljs-keyword">import</span> { readFile } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:fs'</span>; <span class="hljs-title function_">readFile</span>(<span class="hljs-string">'./foo.txt'</span>, <span class="hljs-function">(<span class="hljs-params">err, source</span>) =></span> { <span class="hljs-keyword">if</span> (err) { <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">error</span>(err); } <span class="hljs-keyword">else</span> { <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(source); } });</code> <button class="copy-button">copy</button></pre> <pre><code class="language-js"><span class="hljs-keyword">import</span> fs, { readFileSync } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:fs'</span>; <span class="hljs-keyword">import</span> { syncBuiltinESMExports } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:module'</span>; <span class="hljs-keyword">import</span> { <span class="hljs-title class_">Buffer</span> } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:buffer'</span>; fs.<span class="hljs-property">readFileSync</span> = <span class="hljs-function">() =></span> <span class="hljs-title class_">Buffer</span>.<span class="hljs-title function_">from</span>(<span class="hljs-string">'Hello, ESM'</span>); <span class="hljs-title function_">syncBuiltinESMExports</span>(); fs.<span class="hljs-property">readFileSync</span> === readFileSync;</code> <button class="copy-button">copy</button></pre> </section><section><h3><code>import()</code> expressions<span><a class="mark" href="#import-expressions" id="import-expressions">#</a></span><a aria-hidden="true" class="legacy" id="esm_import_expressions"></a></h3> <p><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/import">Dynamic <code>import()</code></a> provides an asynchronous way to import modules. It is supported in both CommonJS and ES modules, and can be used to load both CommonJS and ES modules.</p> </section><section><h3><code>import.meta</code><span><a class="mark" href="#importmeta" id="importmeta">#</a></span><a aria-hidden="true" class="legacy" id="esm_import_meta"></a></h3> <ul> <li>Type: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li> </ul> <p>The <code>import.meta</code> meta property is an <code>Object</code> that contains the following properties. It is only supported in ES modules.</p> <div> <h4><code>import.meta.dirname</code><span><a class="mark" href="#importmetadirname" id="importmetadirname">#</a></span><a aria-hidden="true" class="legacy" id="esm_import_meta_dirname"></a></h4> <div class="api_metadata"> <details class="changelog"><summary>History</summary> <table> <tbody><tr><th>Version</th><th>Changes</th></tr> <tr><td>v22.16.0</td> <td><p>This property is no longer experimental.</p></td></tr> <tr><td>v21.2.0, v20.11.0</td> <td><p><span>Added in: v21.2.0, v20.11.0</span></p></td></tr> </tbody></table> </details> </div> <ul> <li>Type: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> The directory name of the current module.</li> </ul> <p>This is the same as the <a href="path.html#pathdirnamepath"><code>path.dirname()</code></a> of the <a href="#importmetafilename"><code>import.meta.filename</code></a>.</p> <blockquote> <p><strong>Caveat</strong>: only present on <code>file:</code> modules.</p> </blockquote> </div><div> <h4><code>import.meta.filename</code><span><a class="mark" href="#importmetafilename" id="importmetafilename">#</a></span><a aria-hidden="true" class="legacy" id="esm_import_meta_filename"></a></h4> <div class="api_metadata"> <details class="changelog"><summary>History</summary> <table> <tbody><tr><th>Version</th><th>Changes</th></tr> <tr><td>v22.16.0</td> <td><p>This property is no longer experimental.</p></td></tr> <tr><td>v21.2.0, v20.11.0</td> <td><p><span>Added in: v21.2.0, v20.11.0</span></p></td></tr> </tbody></table> </details> </div> <ul> <li>Type: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> The full absolute path and filename of the current module, with symlinks resolved.</li> </ul> <p>This is the same as the <a href="url.html#urlfileurltopathurl-options"><code>url.fileURLToPath()</code></a> of the <a href="#importmetaurl"><code>import.meta.url</code></a>.</p> <blockquote> <p><strong>Caveat</strong> only local modules support this property. Modules not using the <code>file:</code> protocol will not provide it.</p> </blockquote> </div><div> <h4><code>import.meta.url</code><span><a class="mark" href="#importmetaurl" id="importmetaurl">#</a></span><a aria-hidden="true" class="legacy" id="esm_import_meta_url"></a></h4> <ul> <li>Type: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> The absolute <code>file:</code> URL of the module.</li> </ul> <p>This is defined exactly the same as it is in browsers providing the URL of the current module file.</p> <p>This enables useful patterns such as relative file loading:</p> <pre><code class="language-js"><span class="hljs-keyword">import</span> { readFileSync } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:fs'</span>; <span class="hljs-keyword">const</span> buffer = <span class="hljs-title function_">readFileSync</span>(<span class="hljs-keyword">new</span> <span class="hljs-title function_">URL</span>(<span class="hljs-string">'./data.proto'</span>, <span class="hljs-keyword">import</span>.<span class="hljs-property">meta</span>.<span class="hljs-property">url</span>));</code> <button class="copy-button">copy</button></pre> </div><div> <h4><code>import.meta.main</code><span><a class="mark" href="#importmetamain" id="importmetamain">#</a></span><a aria-hidden="true" class="legacy" id="esm_import_meta_main"></a></h4> <div class="api_metadata"> <span>Added in: v22.18.0</span> </div> <p></p><div class="api_stability api_stability_1"><a href="documentation.html#stability-index">Stability: 1.0</a> - Early development</div><p></p> <ul> <li>Type: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> <code>true</code> when the current module is the entry point of the current process; <code>false</code> otherwise.</li> </ul> <p>Equivalent to <code>require.main === module</code> in CommonJS.</p> <p>Analogous to Python's <code>__name__ == "__main__"</code>.</p> <pre><code class="language-js"><span class="hljs-keyword">export</span> <span class="hljs-keyword">function</span> <span class="hljs-title function_">foo</span>(<span class="hljs-params"></span>) { <span class="hljs-keyword">return</span> <span class="hljs-string">'Hello, world'</span>; } <span class="hljs-keyword">function</span> <span class="hljs-title function_">main</span>(<span class="hljs-params"></span>) { <span class="hljs-keyword">const</span> message = <span class="hljs-title function_">foo</span>(); <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(message); } <span class="hljs-keyword">if</span> (<span class="hljs-keyword">import</span>.<span class="hljs-property">meta</span>.<span class="hljs-property">main</span>) <span class="hljs-title function_">main</span>(); <span class="hljs-comment">// `foo` can be imported from another module without possible side-effects from `main`</span></code> <button class="copy-button">copy</button></pre> </div><div> <h4><code>import.meta.resolve(specifier)</code><span><a class="mark" href="#importmetaresolvespecifier" id="importmetaresolvespecifier">#</a></span><a aria-hidden="true" class="legacy" id="esm_import_meta_resolve_specifier"></a></h4> <div class="api_metadata"> <details class="changelog"><summary>History</summary> <table> <tbody><tr><th>Version</th><th>Changes</th></tr> <tr><td>v20.6.0, v18.19.0</td> <td><p>No longer behind <code>--experimental-import-meta-resolve</code> CLI flag, except for the non-standard <code>parentURL</code> parameter.</p></td></tr> <tr><td>v20.6.0, v18.19.0</td> <td><p>This API no longer throws when targeting <code>file:</code> URLs that do not map to an existing file on the local FS.</p></td></tr> <tr><td>v20.0.0, v18.19.0</td> <td><p>This API now returns a string synchronously instead of a Promise.</p></td></tr> <tr><td>v16.2.0, v14.18.0</td> <td><p>Add support for WHATWG <code>URL</code> object to <code>parentURL</code> parameter.</p></td></tr> <tr><td>v13.9.0, v12.16.2</td> <td><p><span>Added in: v13.9.0, v12.16.2</span></p></td></tr> </tbody></table> </details> </div> <p></p><div class="api_stability api_stability_1"><a href="documentation.html#stability-index">Stability: 1.2</a> - 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> The module specifier to resolve relative to the current module.</li> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> The absolute URL string that the specifier would resolve to.</li> </ul> <p><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/import.meta/resolve"><code>import.meta.resolve</code></a> is a module-relative resolution function scoped to each module, returning the URL string.</p> <pre><code class="language-js"><span class="hljs-keyword">const</span> dependencyAsset = <span class="hljs-keyword">import</span>.<span class="hljs-property">meta</span>.<span class="hljs-title function_">resolve</span>(<span class="hljs-string">'component-lib/asset.css'</span>); <span class="hljs-comment">// file:///app/node_modules/component-lib/asset.css</span> <span class="hljs-keyword">import</span>.<span class="hljs-property">meta</span>.<span class="hljs-title function_">resolve</span>(<span class="hljs-string">'./dep.js'</span>); <span class="hljs-comment">// file:///app/dep.js</span></code> <button class="copy-button">copy</button></pre> <p>All features of the Node.js module resolution are supported. Dependency resolutions are subject to the permitted exports resolutions within the package.</p> <p><strong>Caveats</strong>:</p> <ul> <li>This can result in synchronous file-system operations, which can impact performance similarly to <code>require.resolve</code>.</li> <li>This feature is not available within custom loaders (it would create a deadlock).</li> </ul> <p><strong>Non-standard API</strong>:</p> <p>When using the <code>--experimental-import-meta-resolve</code> flag, that function accepts a second argument:</p> <ul> <li><code>parent</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> An optional absolute parent module URL to resolve from. <strong>Default:</strong> <code>import.meta.url</code></li> </ul> </div> </section><section><h3>Interoperability with CommonJS<span><a class="mark" href="#interoperability-with-commonjs" id="interoperability-with-commonjs">#</a></span><a aria-hidden="true" class="legacy" id="esm_interoperability_with_commonjs"></a></h3> <div> <h4><code>import</code> statements<span><a class="mark" href="#import-statements" id="import-statements">#</a></span><a aria-hidden="true" class="legacy" id="esm_import_statements"></a></h4> <p>An <code>import</code> statement can reference an ES module or a CommonJS module. <code>import</code> statements are permitted only in ES modules, but dynamic <a href="#import-expressions"><code>import()</code></a> expressions are supported in CommonJS for loading ES modules.</p> <p>When importing <a href="#commonjs-namespaces">CommonJS modules</a>, the <code>module.exports</code> object is provided as the default export. Named exports may be available, provided by static analysis as a convenience for better ecosystem compatibility.</p> </div><div> <h4><code>require</code><span><a class="mark" href="#require" id="require">#</a></span><a aria-hidden="true" class="legacy" id="esm_require"></a></h4> <p>The CommonJS module <code>require</code> currently only supports loading synchronous ES modules (that is, ES modules that do not use top-level <code>await</code>).</p> <p>See <a href="modules.html#loading-ecmascript-modules-using-require">Loading ECMAScript modules using <code>require()</code></a> for details.</p> </div><div> <h4>CommonJS Namespaces<span><a class="mark" href="#commonjs-namespaces" id="commonjs-namespaces">#</a></span><a aria-hidden="true" class="legacy" id="esm_commonjs_namespaces"></a></h4> <p>CommonJS modules consist of a <code>module.exports</code> object which can be of any type.</p> <p>When importing a CommonJS module, it can be reliably imported using the ES module default import or its corresponding sugar syntax:</p> <!-- eslint-disable no-duplicate-imports --> <pre><code class="language-js"><span class="hljs-keyword">import</span> { <span class="hljs-keyword">default</span> <span class="hljs-keyword">as</span> cjs } <span class="hljs-keyword">from</span> <span class="hljs-string">'cjs'</span>; <span class="hljs-comment">// The following import statement is "syntax sugar" (equivalent but sweeter)</span> <span class="hljs-comment">// for `{ default as cjsSugar }` in the above import statement:</span> <span class="hljs-keyword">import</span> cjsSugar <span class="hljs-keyword">from</span> <span class="hljs-string">'cjs'</span>; <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(cjs); <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(cjs === cjsSugar); <span class="hljs-comment">// Prints:</span> <span class="hljs-comment">// <module.exports></span> <span class="hljs-comment">// true</span></code> <button class="copy-button">copy</button></pre> <p>The ECMAScript Module Namespace representation of a CommonJS module is always a namespace with a <code>default</code> export key pointing to the CommonJS <code>module.exports</code> value.</p> <p>This Module Namespace Exotic Object can be directly observed either when using <code>import * as m from 'cjs'</code> or a dynamic import:</p> <!-- eslint-skip --> <pre><code class="language-js"><span class="hljs-keyword">import</span> * <span class="hljs-keyword">as</span> m <span class="hljs-keyword">from</span> <span class="hljs-string">'cjs'</span>; <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(m); <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(m === <span class="hljs-keyword">await</span> <span class="hljs-keyword">import</span>(<span class="hljs-string">'cjs'</span>)); <span class="hljs-comment">// Prints:</span> <span class="hljs-comment">// [Module] { default: <module.exports> }</span> <span class="hljs-comment">// true</span></code> <button class="copy-button">copy</button></pre> <p>For better compatibility with existing usage in the JS ecosystem, Node.js in addition attempts to determine the CommonJS named exports of every imported CommonJS module to provide them as separate ES module exports using a static analysis process.</p> <p>For example, consider a CommonJS module written:</p> <pre><code class="language-js cjs"><span class="hljs-comment">// cjs.cjs</span> <span class="hljs-built_in">exports</span>.<span class="hljs-property">name</span> = <span class="hljs-string">'exported'</span>;</code> <button class="copy-button">copy</button></pre> <p>The preceding module supports named imports in ES modules:</p> <!-- eslint-disable no-duplicate-imports --> <pre><code class="language-js"><span class="hljs-keyword">import</span> { name } <span class="hljs-keyword">from</span> <span class="hljs-string">'./cjs.cjs'</span>; <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(name); <span class="hljs-comment">// Prints: 'exported'</span> <span class="hljs-keyword">import</span> cjs <span class="hljs-keyword">from</span> <span class="hljs-string">'./cjs.cjs'</span>; <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(cjs); <span class="hljs-comment">// Prints: { name: 'exported' }</span> <span class="hljs-keyword">import</span> * <span class="hljs-keyword">as</span> m <span class="hljs-keyword">from</span> <span class="hljs-string">'./cjs.cjs'</span>; <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(m); <span class="hljs-comment">// Prints: [Module] { default: { name: 'exported' }, name: 'exported' }</span></code> <button class="copy-button">copy</button></pre> <p>As can be seen from the last example of the Module Namespace Exotic Object being logged, the <code>name</code> export is copied off of the <code>module.exports</code> object and set directly on the ES module namespace when the module is imported.</p> <p>Live binding updates or new exports added to <code>module.exports</code> are not detected for these named exports.</p> <p>The detection of named exports is based on common syntax patterns but does not always correctly detect named exports. In these cases, using the default import form described above can be a better option.</p> <p>Named exports detection covers many common export patterns, reexport patterns and build tool and transpiler outputs. See <a href="https://github.com/nodejs/cjs-module-lexer/tree/2.0.0">cjs-module-lexer</a> for the exact semantics implemented.</p> </div><div> <h4>Differences between ES modules and CommonJS<span><a class="mark" href="#differences-between-es-modules-and-commonjs" id="differences-between-es-modules-and-commonjs">#</a></span><a aria-hidden="true" class="legacy" id="esm_differences_between_es_modules_and_commonjs"></a></h4> <div> <h5>No <code>require</code>, <code>exports</code>, or <code>module.exports</code><span><a class="mark" href="#no-require-exports-or-moduleexports" id="no-require-exports-or-moduleexports">#</a></span><a aria-hidden="true" class="legacy" id="esm_no_require_exports_or_module_exports"></a></h5> <p>In most cases, the ES module <code>import</code> can be used to load CommonJS modules.</p> <p>If needed, a <code>require</code> function can be constructed within an ES module using <a href="module.html#modulecreaterequirefilename"><code>module.createRequire()</code></a>.</p> </div><div> <h5>No <code>__filename</code> or <code>__dirname</code><span><a class="mark" href="#no-__filename-or-__dirname" id="no-__filename-or-__dirname">#</a></span><a aria-hidden="true" class="legacy" id="esm_no_filename_or_dirname"></a></h5> <p>These CommonJS variables are not available in ES modules.</p> <p><code>__filename</code> and <code>__dirname</code> use cases can be replicated via <a href="#importmetafilename"><code>import.meta.filename</code></a> and <a href="#importmetadirname"><code>import.meta.dirname</code></a>.</p> </div><div> <h5>No Addon Loading<span><a class="mark" href="#no-addon-loading" id="no-addon-loading">#</a></span><a aria-hidden="true" class="legacy" id="esm_no_addon_loading"></a></h5> <p><a href="addons.html">Addons</a> are not currently supported with ES module imports.</p> <p>They can instead be loaded with <a href="module.html#modulecreaterequirefilename"><code>module.createRequire()</code></a> or <a href="process.html#processdlopenmodule-filename-flags"><code>process.dlopen</code></a>.</p> </div><div> <h5>No <code>require.main</code><span><a class="mark" href="#no-requiremain" id="no-requiremain">#</a></span><a aria-hidden="true" class="legacy" id="esm_no_require_main"></a></h5> <p>To replace <code>require.main === module</code>, there is the <a href="#importmetamain"><code>import.meta.main</code></a> API.</p> </div><div> <h5>No <code>require.resolve</code><span><a class="mark" href="#no-requireresolve" id="no-requireresolve">#</a></span><a aria-hidden="true" class="legacy" id="esm_no_require_resolve"></a></h5> <p>Relative resolution can be handled via <code>new URL('./local', import.meta.url)</code>.</p> <p>For a complete <code>require.resolve</code> replacement, there is the <a href="#importmetaresolvespecifier">import.meta.resolve</a> API.</p> <p>Alternatively <code>module.createRequire()</code> can be used.</p> </div><div> <h5>No <code>NODE_PATH</code><span><a class="mark" href="#no-node_path" id="no-node_path">#</a></span><a aria-hidden="true" class="legacy" id="esm_no_node_path"></a></h5> <p><code>NODE_PATH</code> is not part of resolving <code>import</code> specifiers. Please use symlinks if this behavior is desired.</p> </div><div> <h5>No <code>require.extensions</code><span><a class="mark" href="#no-requireextensions" id="no-requireextensions">#</a></span><a aria-hidden="true" class="legacy" id="esm_no_require_extensions"></a></h5> <p><code>require.extensions</code> is not used by <code>import</code>. Module customization hooks can provide a replacement.</p> </div><div> <h5>No <code>require.cache</code><span><a class="mark" href="#no-requirecache" id="no-requirecache">#</a></span><a aria-hidden="true" class="legacy" id="esm_no_require_cache"></a></h5> <p><code>require.cache</code> is not used by <code>import</code> as the ES module loader has its own separate cache.</p> <p><i id="esm_experimental_json_modules"></i></p> </div></div> </section><section><h3>JSON modules<span><a class="mark" href="#json-modules" id="json-modules">#</a></span><a aria-hidden="true" class="legacy" id="esm_json_modules"></a></h3> <div class="api_metadata"> <details class="changelog"><summary>History</summary> <table> <tbody><tr><th>Version</th><th>Changes</th></tr> <tr><td>v22.12.0</td> <td><p>JSON modules are no longer experimental.</p></td></tr> </tbody></table> </details> </div> <p>JSON files can be referenced by <code>import</code>:</p> <pre><code class="language-js"><span class="hljs-keyword">import</span> packageConfig <span class="hljs-keyword">from</span> <span class="hljs-string">'./package.json'</span> <span class="hljs-keyword">with</span> { <span class="hljs-attr">type</span>: <span class="hljs-string">'json'</span> };</code> <button class="copy-button">copy</button></pre> <p>The <code>with { type: 'json' }</code> syntax is mandatory; see <a href="#import-attributes">Import Attributes</a>.</p> <p>The imported JSON only exposes a <code>default</code> export. There is no support for named exports. A cache entry is created in the CommonJS cache to avoid duplication. The same object is returned in CommonJS if the JSON module has already been imported from the same path.</p> <p><i id="esm_experimental_wasm_modules"></i></p> </section><section><h3>Wasm modules<span><a class="mark" href="#wasm-modules" id="wasm-modules">#</a></span><a aria-hidden="true" class="legacy" id="esm_wasm_modules"></a></h3> <div class="api_metadata"> <details class="changelog"><summary>History</summary> <table> <tbody><tr><th>Version</th><th>Changes</th></tr> <tr><td>v22.19.0</td> <td><p>Wasm modules no longer require the <code>--experimental-wasm-modules</code> flag.</p></td></tr> </tbody></table> </details> </div> <p>Importing both WebAssembly module instances and WebAssembly source phase imports is supported.</p> <p>This integration is in line with the <a href="https://github.com/webassembly/esm-integration">ES Module Integration Proposal for WebAssembly</a>.</p> </section><section><h3>Wasm modules<span><a class="mark" href="#wasm-modules_1" id="wasm-modules_1">#</a></span><a aria-hidden="true" class="legacy" id="esm_wasm_modules_1"></a></h3> <p></p><div class="api_stability api_stability_1"><a href="documentation.html#stability-index">Stability: 1</a> - Experimental</div><p></p> <p>Importing WebAssembly modules is supported allowing any <code>.wasm</code> files to be imported as normal modules while also supporting their module imports.</p> <p>This integration is in line with the <a href="https://github.com/webassembly/esm-integration">ES Module Integration Proposal for WebAssembly</a>.</p> <p>For example, an <code>index.mjs</code> containing:</p> <pre><code class="language-js"><span class="hljs-keyword">import</span> * <span class="hljs-keyword">as</span> M <span class="hljs-keyword">from</span> <span class="hljs-string">'./module.wasm'</span>; <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(M);</code> <button class="copy-button">copy</button></pre> <p>executed under:</p> <pre><code class="language-bash">node index.mjs</code> <button class="copy-button">copy</button></pre> <p>would provide the exports interface for the instantiation of <code>module.wasm</code>.</p> <div> <h4>JavaScript String Builtins<span><a class="mark" href="#javascript-string-builtins" id="javascript-string-builtins">#</a></span><a aria-hidden="true" class="legacy" id="esm_javascript_string_builtins"></a></h4> <div class="api_metadata"> <span>Added in: v22.19.0</span> </div> <p>When importing WebAssembly modules, the <a href="https://github.com/WebAssembly/js-string-builtins">WebAssembly JS String Builtins Proposal</a> is automatically enabled through the ESM Integration. This allows WebAssembly modules to directly use efficient compile-time string builtins from the <code>wasm:js-string</code> namespace.</p> <p>For example, the following Wasm module exports a string <code>getLength</code> function using the <code>wasm:js-string</code> <code>length</code> builtin:</p> <pre><code class="language-text">(module ;; Compile-time import of the string length builtin. (import "wasm:js-string" "length" (func $string_length (param externref) (result i32))) ;; Define getLength, taking a JS value parameter assumed to be a string, ;; calling string length on it and returning the result. (func $getLength (param $str externref) (result i32) local.get $str call $string_length ) ;; Export the getLength function. (export "getLength" (func $get_length)) )</code> <button class="copy-button">copy</button></pre> <pre><code class="language-js"><span class="hljs-keyword">import</span> { getLength } <span class="hljs-keyword">from</span> <span class="hljs-string">'./string-len.wasm'</span>; <span class="hljs-title function_">getLength</span>(<span class="hljs-string">'foo'</span>); <span class="hljs-comment">// Returns 3.</span></code> <button class="copy-button">copy</button></pre> <p>Wasm builtins are compile-time imports that are linked during module compilation rather than during instantiation. They do not behave like normal module graph imports and they cannot be inspected via <code>WebAssembly.Module.imports(mod)</code> or virtualized unless recompiling the module using the direct <code>WebAssembly.compile</code> API with string builtins disabled.</p> </div><div> <h4>Reserved Wasm Namespaces<span><a class="mark" href="#reserved-wasm-namespaces" id="reserved-wasm-namespaces">#</a></span><a aria-hidden="true" class="legacy" id="esm_reserved_wasm_namespaces"></a></h4> <div class="api_metadata"> <span>Added in: v22.19.0</span> </div> <p>When importing WebAssembly modules through the ESM Integration, they cannot use import module names or import/export names that start with reserved prefixes:</p> <ul> <li><code>wasm-js:</code> - reserved in all module import names, module names and export names.</li> <li><code>wasm:</code> - reserved in module import names and export names (imported module names are allowed in order to support future builtin polyfills).</li> </ul> <p>Importing a module using the above reserved names will throw a <code>WebAssembly.LinkError</code>.</p> <p><i id="esm_experimental_top_level_await"></i></p> </div> </section><section><h3>Top-level <code>await</code><span><a class="mark" href="#top-level-await" id="top-level-await">#</a></span><a aria-hidden="true" class="legacy" id="esm_top_level_await"></a></h3> <div class="api_metadata"> <span>Added in: v14.8.0</span> </div> <p>The <code>await</code> keyword may be used in the top level body of an ECMAScript module.</p> <p>Assuming an <code>a.mjs</code> with</p> <pre><code class="language-js"><span class="hljs-keyword">export</span> <span class="hljs-keyword">const</span> five = <span class="hljs-keyword">await</span> <span class="hljs-title class_">Promise</span>.<span class="hljs-title function_">resolve</span>(<span class="hljs-number">5</span>);</code> <button class="copy-button">copy</button></pre> <p>And a <code>b.mjs</code> with</p> <pre><code class="language-js"><span class="hljs-keyword">import</span> { five } <span class="hljs-keyword">from</span> <span class="hljs-string">'./a.mjs'</span>; <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(five); <span class="hljs-comment">// Logs `5`</span></code> <button class="copy-button">copy</button></pre> <pre><code class="language-bash">node b.mjs <span class="hljs-comment"># works</span></code> <button class="copy-button">copy</button></pre> <p>If a top level <code>await</code> expression never resolves, the <code>node</code> process will exit with a <code>13</code> <a href="process.html#exit-codes">status code</a>.</p> <pre><code class="language-js"><span class="hljs-keyword">import</span> { spawn } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:child_process'</span>; <span class="hljs-keyword">import</span> { execPath } <span class="hljs-keyword">from</span> <span class="hljs-string">'node:process'</span>; <span class="hljs-title function_">spawn</span>(execPath, [ <span class="hljs-string">'--input-type=module'</span>, <span class="hljs-string">'--eval'</span>, <span class="hljs-comment">// Never-resolving Promise:</span> <span class="hljs-string">'await new Promise(() => {})'</span>, ]).<span class="hljs-title function_">once</span>(<span class="hljs-string">'exit'</span>, <span class="hljs-function">(<span class="hljs-params">code</span>) =></span> { <span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(code); <span class="hljs-comment">// Logs `13`</span> });</code> <button class="copy-button">copy</button></pre> <p><i id="esm_experimental_loaders"></i></p> </section><section><h3>Loaders<span><a class="mark" href="#loaders" id="loaders">#</a></span><a aria-hidden="true" class="legacy" id="esm_loaders"></a></h3> <p>The former Loaders documentation is now at <a href="module.html#customization-hooks">Modules: Customization hooks</a>.</p> </section><section><h3>Resolution and loading algorithm<span><a class="mark" href="#resolution-and-loading-algorithm" id="resolution-and-loading-algorithm">#</a></span><a aria-hidden="true" class="legacy" id="esm_resolution_and_loading_algorithm"></a></h3> <div> <h4>Features<span><a class="mark" href="#features" id="features">#</a></span><a aria-hidden="true" class="legacy" id="esm_features"></a></h4> <p>The default resolver has the following properties:</p> <ul> <li>FileURL-based resolution as is used by ES modules</li> <li>Relative and absolute URL resolution</li> <li>No default extensions</li> <li>No folder mains</li> <li>Bare specifier package resolution lookup through node_modules</li> <li>Does not fail on unknown extensions or protocols</li> <li>Can optionally provide a hint of the format to the loading phase</li> </ul> <p>The default loader has the following properties</p> <ul> <li>Support for builtin module loading via <code>node:</code> URLs</li> <li>Support for "inline" module loading via <code>data:</code> URLs</li> <li>Support for <code>file:</code> module loading</li> <li>Fails on any other URL protocol</li> <li>Fails on unknown extensions for <code>file:</code> loading (supports only <code>.cjs</code>, <code>.js</code>, and <code>.mjs</code>)</li> </ul> </div><div> <h4>Resolution algorithm<span><a class="mark" href="#resolution-algorithm" id="resolution-algorithm">#</a></span><a aria-hidden="true" class="legacy" id="esm_resolution_algorithm"></a></h4> <p>The algorithm to load an ES module specifier is given through the <strong>ESM_RESOLVE</strong> method below. It returns the resolved URL for a module specifier relative to a parentURL.</p> <p>The resolution algorithm determines the full resolved URL for a module load, along with its suggested module format. The resolution algorithm does not determine whether the resolved URL protocol can be loaded, or whether the file extensions are permitted, instead these validations are applied by Node.js during the load phase (for example, if it was asked to load a URL that has a protocol that is not <code>file:</code>, <code>data:</code> or <code>node:</code>.</p> <p>The algorithm also tries to determine the format of the file based on the extension (see <code>ESM_FILE_FORMAT</code> algorithm below). If it does not recognize the file extension (eg if it is not <code>.mjs</code>, <code>.cjs</code>, or <code>.json</code>), then a format of <code>undefined</code> is returned, which will throw during the load phase.</p> <p>The algorithm to determine the module format of a resolved URL is provided by <strong>ESM_FILE_FORMAT</strong>, which returns the unique module format for any file. The <em>"module"</em> format is returned for an ECMAScript Module, while the <em>"commonjs"</em> format is used to indicate loading through the legacy CommonJS loader. Additional formats such as <em>"addon"</em> can be extended in future updates.</p> <p>In the following algorithms, all subroutine errors are propagated as errors of these top-level routines unless stated otherwise.</p> <p><em>defaultConditions</em> is the conditional environment name array, <code>["node", "import"]</code>.</p> <p>The resolver can throw the following errors:</p> <ul> <li><em>Invalid Module Specifier</em>: Module specifier is an invalid URL, package name or package subpath specifier.</li> <li><em>Invalid Package Configuration</em>: package.json configuration is invalid or contains an invalid configuration.</li> <li><em>Invalid Package Target</em>: Package exports or imports define a target module for the package that is an invalid type or string target.</li> <li><em>Package Path Not Exported</em>: Package exports do not define or permit a target subpath in the package for the given module.</li> <li><em>Package Import Not Defined</em>: Package imports do not define the specifier.</li> <li><em>Module Not Found</em>: The package or module requested does not exist.</li> <li><em>Unsupported Directory Import</em>: The resolved path corresponds to a directory, which is not a supported target for module imports.</li> </ul> </div><div> <h4>Resolution Algorithm Specification<span><a class="mark" href="#resolution-algorithm-specification" id="resolution-algorithm-specification">#</a></span><a aria-hidden="true" class="legacy" id="esm_resolution_algorithm_specification"></a></h4> <p><strong>ESM_RESOLVE</strong>(<em>specifier</em>, <em>parentURL</em>)</p> <blockquote> <ol> <li>Let <em>resolved</em> be <strong>undefined</strong>.</li> <li>If <em>specifier</em> is a valid URL, then <ol> <li>Set <em>resolved</em> to the result of parsing and reserializing <em>specifier</em> as a URL.</li> </ol> </li> <li>Otherwise, if <em>specifier</em> starts with <em>"/"</em>, <em>"./"</em>, or <em>"../"</em>, then <ol> <li>Set <em>resolved</em> to the URL resolution of <em>specifier</em> relative to <em>parentURL</em>.</li> </ol> </li> <li>Otherwise, if <em>specifier</em> starts with <em>"#"</em>, then <ol> <li>Set <em>resolved</em> to the result of <strong>PACKAGE_IMPORTS_RESOLVE</strong>(<em>specifier</em>, <em>parentURL</em>, <em>defaultConditions</em>).</li> </ol> </li> <li>Otherwise, <ol> <li>Note: <em>specifier</em> is now a bare specifier.</li> <li>Set <em>resolved</em> the result of <strong>PACKAGE_RESOLVE</strong>(<em>specifier</em>, <em>parentURL</em>).</li> </ol> </li> <li>Let <em>format</em> be <strong>undefined</strong>.</li> <li>If <em>resolved</em> is a <em>"file:"</em> URL, then <ol> <li>If <em>resolved</em> contains any percent encodings of <em>"/"</em> or <em>"\"</em> (<em>"%2F"</em> and <em>"%5C"</em> respectively), then <ol> <li>Throw an <em>Invalid Module Specifier</em> error.</li> </ol> </li> <li>If the file at <em>resolved</em> is a directory, then <ol> <li>Throw an <em>Unsupported Directory Import</em> error.</li> </ol> </li> <li>If the file at <em>resolved</em> does not exist, then <ol> <li>Throw a <em>Module Not Found</em> error.</li> </ol> </li> <li>Set <em>resolved</em> to the real path of <em>resolved</em>, maintaining the same URL querystring and fragment components.</li> <li>Set <em>format</em> to the result of <strong>ESM_FILE_FORMAT</strong>(<em>resolved</em>).</li> </ol> </li> <li>Otherwise, <ol> <li>Set <em>format</em> the module format of the content type associated with the URL <em>resolved</em>.</li> </ol> </li> <li>Return <em>format</em> and <em>resolved</em> to the loading phase</li> </ol> </blockquote> <p><strong>PACKAGE_RESOLVE</strong>(<em>packageSpecifier</em>, <em>parentURL</em>)</p> <blockquote> <ol> <li>Let <em>packageName</em> be <strong>undefined</strong>.</li> <li>If <em>packageSpecifier</em> is an empty string, then <ol> <li>Throw an <em>Invalid Module Specifier</em> error.</li> </ol> </li> <li>If <em>packageSpecifier</em> is a Node.js builtin module name, then <ol> <li>Return the string <em>"node:"</em> concatenated with <em>packageSpecifier</em>.</li> </ol> </li> <li>If <em>packageSpecifier</em> does not start with <em>"@"</em>, then <ol> <li>Set <em>packageName</em> to the substring of <em>packageSpecifier</em> until the first <em>"/"</em> separator or the end of the string.</li> </ol> </li> <li>Otherwise, <ol> <li>If <em>packageSpecifier</em> does not contain a <em>"/"</em> separator, then <ol> <li>Throw an <em>Invalid Module Specifier</em> error.</li> </ol> </li> <li>Set <em>packageName</em> to the substring of <em>packageSpecifier</em> until the second <em>"/"</em> separator or the end of the string.</li> </ol> </li> <li>If <em>packageName</em> starts with <em>"."</em> or contains <em>"\"</em> or <em>"%"</em>, then <ol> <li>Throw an <em>Invalid Module Specifier</em> error.</li> </ol> </li> <li>Let <em>packageSubpath</em> be <em>"."</em> concatenated with the substring of <em>packageSpecifier</em> from the position at the length of <em>packageName</em>.</li> <li>Let <em>selfUrl</em> be the result of <strong>PACKAGE_SELF_RESOLVE</strong>(<em>packageName</em>, <em>packageSubpath</em>, <em>parentURL</em>).</li> <li>If <em>selfUrl</em> is not <strong>undefined</strong>, return <em>selfUrl</em>.</li> <li>While <em>parentURL</em> is not the file system root, <ol> <li>Let <em>packageURL</em> be the URL resolution of <em>"node_modules/"</em> concatenated with <em>packageName</em>, relative to <em>parentURL</em>.</li> <li>Set <em>parentURL</em> to the parent folder URL of <em>parentURL</em>.</li> <li>If the folder at <em>packageURL</em> does not exist, then <ol> <li>Continue the next loop iteration.</li> </ol> </li> <li>Let <em>pjson</em> be the result of <strong>READ_PACKAGE_JSON</strong>(<em>packageURL</em>).</li> <li>If <em>pjson</em> is not <strong>null</strong> and <em>pjson</em>.<em>exports</em> is not <strong>null</strong> or <strong>undefined</strong>, then <ol> <li>Return the result of <strong>PACKAGE_EXPORTS_RESOLVE</strong>(<em>packageURL</em>, <em>packageSubpath</em>, <em>pjson.exports</em>, <em>defaultConditions</em>).</li> </ol> </li> <li>Otherwise, if <em>packageSubpath</em> is equal to <em>"."</em>, then <ol> <li>If <em>pjson.main</em> is a string, then <ol> <li>Return the URL resolution of <em>main</em> in <em>packageURL</em>.</li> </ol> </li> </ol> </li> <li>Otherwise, <ol> <li>Return the URL resolution of <em>packageSubpath</em> in <em>packageURL</em>.</li> </ol> </li> </ol> </li> <li>Throw a <em>Module Not Found</em> error.</li> </ol> </blockquote> <p><strong>PACKAGE_SELF_RESOLVE</strong>(<em>packageName</em>, <em>packageSubpath</em>, <em>parentURL</em>)</p> <blockquote> <ol> <li>Let <em>packageURL</em> be the result of <strong>LOOKUP_PACKAGE_SCOPE</strong>(<em>parentURL</em>).</li> <li>If <em>packageURL</em> is <strong>null</strong>, then <ol> <li>Return <strong>undefined</strong>.</li> </ol> </li> <li>Let <em>pjson</em> be the result of <strong>READ_PACKAGE_JSON</strong>(<em>packageURL</em>).</li> <li>If <em>pjson</em> is <strong>null</strong> or if <em>pjson</em>.<em>exports</em> is <strong>null</strong> or <strong>undefined</strong>, then <ol> <li>Return <strong>undefined</strong>.</li> </ol> </li> <li>If <em>pjson.name</em> is equal to <em>packageName</em>, then <ol> <li>Return the result of <strong>PACKAGE_EXPORTS_RESOLVE</strong>(<em>packageURL</em>, <em>packageSubpath</em>, <em>pjson.exports</em>, <em>defaultConditions</em>).</li> </ol> </li> <li>Otherwise, return <strong>undefined</strong>.</li> </ol> </blockquote> <p><strong>PACKAGE_EXPORTS_RESOLVE</strong>(<em>packageURL</em>, <em>subpath</em>, <em>exports</em>, <em>conditions</em>)</p> <p>Note: This function is directly invoked by the CommonJS resolution algorithm.</p> <blockquote> <ol> <li>If <em>exports</em> is an Object with both a key starting with <em>"."</em> and a key not starting with <em>"."</em>, throw an <em>Invalid Package Configuration</em> error.</li> <li>If <em>subpath</em> is equal to <em>"."</em>, then <ol> <li>Let <em>mainExport</em> be <strong>undefined</strong>.</li> <li>If <em>exports</em> is a String or Array, or an Object containing no keys starting with <em>"."</em>, then <ol> <li>Set <em>mainExport</em> to <em>exports</em>.</li> </ol> </li> <li>Otherwise if <em>exports</em> is an Object containing a <em>"."</em> property, then <ol> <li>Set <em>mainExport</em> to <em>exports</em>[<em>"."</em>].</li> </ol> </li> <li>If <em>mainExport</em> is not <strong>undefined</strong>, then <ol> <li>Let <em>resolved</em> be the result of <strong>PACKAGE_TARGET_RESOLVE</strong>( <em>packageURL</em>, <em>mainExport</em>, <strong>null</strong>, <strong>false</strong>, <em>conditions</em>).</li> <li>If <em>resolved</em> is not <strong>null</strong> or <strong>undefined</strong>, return <em>resolved</em>.</li> </ol> </li> </ol> </li> <li>Otherwise, if <em>exports</em> is an Object and all keys of <em>exports</em> start with <em>"."</em>, then <ol> <li>Assert: <em>subpath</em> begins with <em>"./"</em>.</li> <li>Let <em>resolved</em> be the result of <strong>PACKAGE_IMPORTS_EXPORTS_RESOLVE</strong>( <em>subpath</em>, <em>exports</em>, <em>packageURL</em>, <strong>false</strong>, <em>conditions</em>).</li> <li>If <em>resolved</em> is not <strong>null</strong> or <strong>undefined</strong>, return <em>resolved</em>.</li> </ol> </li> <li>Throw a <em>Package Path Not Exported</em> error.</li> </ol> </blockquote> <p><strong>PACKAGE_IMPORTS_RESOLVE</strong>(<em>specifier</em>, <em>parentURL</em>, <em>conditions</em>)</p> <p>Note: This function is directly invoked by the CommonJS resolution algorithm.</p> <blockquote> <ol> <li>Assert: <em>specifier</em> begins with <em>"#"</em>.</li> <li>If <em>specifier</em> is exactly equal to <em>"#"</em> or starts with <em>"#/"</em>, then <ol> <li>Throw an <em>Invalid Module Specifier</em> error.</li> </ol> </li> <li>Let <em>packageURL</em> be the result of <strong>LOOKUP_PACKAGE_SCOPE</strong>(<em>parentURL</em>).</li> <li>If <em>packageURL</em> is not <strong>null</strong>, then <ol> <li>Let <em>pjson</em> be the result of <strong>READ_PACKAGE_JSON</strong>(<em>packageURL</em>).</li> <li>If <em>pjson.imports</em> is a non-null Object, then <ol> <li>Let <em>resolved</em> be the result of <strong>PACKAGE_IMPORTS_EXPORTS_RESOLVE</strong>( <em>specifier</em>, <em>pjson.imports</em>, <em>packageURL</em>, <strong>true</strong>, <em>conditions</em>).</li> <li>If <em>resolved</em> is not <strong>null</strong> or <strong>undefined</strong>, return <em>resolved</em>.</li> </ol> </li> </ol> </li> <li>Throw a <em>Package Import Not Defined</em> error.</li> </ol> </blockquote> <p><strong>PACKAGE_IMPORTS_EXPORTS_RESOLVE</strong>(<em>matchKey</em>, <em>matchObj</em>, <em>packageURL</em>, <em>isImports</em>, <em>conditions</em>)</p> <blockquote> <ol> <li>If <em>matchKey</em> ends in <em>"/"</em>, then <ol> <li>Throw an <em>Invalid Module Specifier</em> error.</li> </ol> </li> <li>If <em>matchKey</em> is a key of <em>matchObj</em> and does not contain <em>"*"</em>, then <ol> <li>Let <em>target</em> be the value of <em>matchObj</em>[<em>matchKey</em>].</li> <li>Return the result of <strong>PACKAGE_TARGET_RESOLVE</strong>(<em>packageURL</em>, <em>target</em>, <strong>null</strong>, <em>isImports</em>, <em>conditions</em>).</li> </ol> </li> <li>Let <em>expansionKeys</em> be the list of keys of <em>matchObj</em> containing only a single <em>"*"</em>, sorted by the sorting function <strong>PATTERN_KEY_COMPARE</strong> which orders in descending order of specificity.</li> <li>For each key <em>expansionKey</em> in <em>expansionKeys</em>, do <ol> <li>Let <em>patternBase</em> be the substring of <em>expansionKey</em> up to but excluding the first <em>"*"</em> character.</li> <li>If <em>matchKey</em> starts with but is not equal to <em>patternBase</em>, then <ol> <li>Let <em>patternTrailer</em> be the substring of <em>expansionKey</em> from the index after the first <em>"*"</em> character.</li> <li>If <em>patternTrailer</em> has zero length, or if <em>matchKey</em> ends with <em>patternTrailer</em> and the length of <em>matchKey</em> is greater than or equal to the length of <em>expansionKey</em>, then <ol> <li>Let <em>target</em> be the value of <em>matchObj</em>[<em>expansionKey</em>].</li> <li>Let <em>patternMatch</em> be the substring of <em>matchKey</em> starting at the index of the length of <em>patternBase</em> up to the length of <em>matchKey</em> minus the length of <em>patternTrailer</em>.</li> <li>Return the result of <strong>PACKAGE_TARGET_RESOLVE</strong>(<em>packageURL</em>, <em>target</em>, <em>patternMatch</em>, <em>isImports</em>, <em>conditions</em>).</li> </ol> </li> </ol> </li> </ol> </li> <li>Return <strong>null</strong>.</li> </ol> </blockquote> <p><strong>PATTERN_KEY_COMPARE</strong>(<em>keyA</em>, <em>keyB</em>)</p> <blockquote> <ol> <li>Assert: <em>keyA</em> contains only a single <em>"*"</em>.</li> <li>Assert: <em>keyB</em> contains only a single <em>"*"</em>.</li> <li>Let <em>baseLengthA</em> be the index of <em>"*"</em> in <em>keyA</em>.</li> <li>Let <em>baseLengthB</em> be the index of <em>"*"</em> in <em>keyB</em>.</li> <li>If <em>baseLengthA</em> is greater than <em>baseLengthB</em>, return -1.</li> <li>If <em>baseLengthB</em> is greater than <em>baseLengthA</em>, return 1.</li> <li>If the length of <em>keyA</em> is greater than the length of <em>keyB</em>, return -1.</li> <li>If the length of <em>keyB</em> is greater than the length of <em>keyA</em>, return 1.</li> <li>Return 0.</li> </ol> </blockquote> <p><strong>PACKAGE_TARGET_RESOLVE</strong>(<em>packageURL</em>, <em>target</em>, <em>patternMatch</em>, <em>isImports</em>, <em>conditions</em>)</p> <blockquote> <ol> <li>If <em>target</em> is a String, then <ol> <li>If <em>target</em> does not start with <em>"./"</em>, then <ol> <li>If <em>isImports</em> is <strong>false</strong>, or if <em>target</em> starts with <em>"../"</em> or <em>"/"</em>, or if <em>target</em> is a valid URL, then <ol> <li>Throw an <em>Invalid Package Target</em> error.</li> </ol> </li> <li>If <em>patternMatch</em> is a String, then <ol> <li>Return <strong>PACKAGE_RESOLVE</strong>(<em>target</em> with every instance of <em>"*"</em> replaced by <em>patternMatch</em>, <em>packageURL</em> + <em>"/"</em>).</li> </ol> </li> <li>Return <strong>PACKAGE_RESOLVE</strong>(<em>target</em>, <em>packageURL</em> + <em>"/"</em>).</li> </ol> </li> <li>If <em>target</em> split on <em>"/"</em> or <em>"\"</em> contains any <em>""</em>, <em>"."</em>, <em>".."</em>, or <em>"node_modules"</em> segments after the first <em>"."</em> segment, case insensitive and including percent encoded variants, throw an <em>Invalid Package Target</em> error.</li> <li>Let <em>resolvedTarget</em> be the URL resolution of the concatenation of <em>packageURL</em> and <em>target</em>.</li> <li>Assert: <em>packageURL</em> is contained in <em>resolvedTarget</em>.</li> <li>If <em>patternMatch</em> is <strong>null</strong>, then <ol> <li>Return <em>resolvedTarget</em>.</li> </ol> </li> <li>If <em>patternMatch</em> split on <em>"/"</em> or <em>"\"</em> contains any <em>""</em>, <em>"."</em>, <em>".."</em>, or <em>"node_modules"</em> segments, case insensitive and including percent encoded variants, throw an <em>Invalid Module Specifier</em> error.</li> <li>Return the URL resolution of <em>resolvedTarget</em> with every instance of <em>"*"</em> replaced with <em>patternMatch</em>.</li> </ol> </li> <li>Otherwise, if <em>target</em> is a non-null Object, then <ol> <li>If <em>target</em> contains any index property keys, as defined in ECMA-262 <a href="https://tc39.es/ecma262/#integer-index">6.1.7 Array Index</a>, throw an <em>Invalid Package Configuration</em> error.</li> <li>For each property <em>p</em> of <em>target</em>, in object insertion order as, <ol> <li>If <em>p</em> equals <em>"default"</em> or <em>conditions</em> contains an entry for <em>p</em>, then <ol> <li>Let <em>targetValue</em> be the value of the <em>p</em> property in <em>target</em>.</li> <li>Let <em>resolved</em> be the result of <strong>PACKAGE_TARGET_RESOLVE</strong>( <em>packageURL</em>, <em>targetValue</em>, <em>patternMatch</em>, <em>isImports</em>, <em>conditions</em>).</li> <li>If <em>resolved</em> is equal to <strong>undefined</strong>, continue the loop.</li> <li>Return <em>resolved</em>.</li> </ol> </li> </ol> </li> <li>Return <strong>undefined</strong>.</li> </ol> </li> <li>Otherwise, if <em>target</em> is an Array, then <ol> <li>If _target.length is zero, return <strong>null</strong>.</li> <li>For each item <em>targetValue</em> in <em>target</em>, do <ol> <li>Let <em>resolved</em> be the result of <strong>PACKAGE_TARGET_RESOLVE</strong>( <em>packageURL</em>, <em>targetValue</em>, <em>patternMatch</em>, <em>isImports</em>, <em>conditions</em>), continuing the loop on any <em>Invalid Package Target</em> error.</li> <li>If <em>resolved</em> is <strong>undefined</strong>, continue the loop.</li> <li>Return <em>resolved</em>.</li> </ol> </li> <li>Return or throw the last fallback resolution <strong>null</strong> return or error.</li> </ol> </li> <li>Otherwise, if <em>target</em> is <em>null</em>, return <strong>null</strong>.</li> <li>Otherwise throw an <em>Invalid Package Target</em> error.</li> </ol> </blockquote> <p><strong>ESM_FILE_FORMAT</strong>(<em>url</em>)</p> <blockquote> <ol> <li>Assert: <em>url</em> corresponds to an existing file.</li> <li>If <em>url</em> ends in <em>".mjs"</em>, then <ol> <li>Return <em>"module"</em>.</li> </ol> </li> <li>If <em>url</em> ends in <em>".cjs"</em>, then <ol> <li>Return <em>"commonjs"</em>.</li> </ol> </li> <li>If <em>url</em> ends in <em>".json"</em>, then <ol> <li>Return <em>"json"</em>.</li> </ol> </li> <li>If <em>url</em> ends in <em>".wasm"</em>, then <ol> <li>Return <em>"wasm"</em>.</li> </ol> </li> <li>If <code>--experimental-addon-modules</code> is enabled and <em>url</em> ends in <em>".node"</em>, then <ol> <li>Return <em>"addon"</em>.</li> </ol> </li> <li>Let <em>packageURL</em> be the result of <strong>LOOKUP_PACKAGE_SCOPE</strong>(<em>url</em>).</li> <li>Let <em>pjson</em> be the result of <strong>READ_PACKAGE_JSON</strong>(<em>packageURL</em>).</li> <li>Let <em>packageType</em> be <strong>null</strong>.</li> <li>If <em>pjson?.type</em> is <em>"module"</em> or <em>"commonjs"</em>, then <ol> <li>Set <em>packageType</em> to <em>pjson.type</em>.</li> </ol> </li> <li>If <em>url</em> ends in <em>".js"</em>, then <ol> <li>If <em>packageType</em> is not <strong>null</strong>, then <ol> <li>Return <em>packageType</em>.</li> </ol> </li> <li>If the result of <strong>DETECT_MODULE_SYNTAX</strong>(<em>source</em>) is true, then <ol> <li>Return <em>"module"</em>.</li> </ol> </li> <li>Return <em>"commonjs"</em>.</li> </ol> </li> <li>If <em>url</em> does not have any extension, then <ol> <li>If <em>packageType</em> is <em>"module"</em> and the file at <em>url</em> contains the header for a WebAssembly module, then <ol> <li>Return <em>"wasm"</em>.</li> </ol> </li> <li>If <em>packageType</em> is not <strong>null</strong>, then <ol> <li>Return <em>packageType</em>.</li> </ol> </li> <li>If the result of <strong>DETECT_MODULE_SYNTAX</strong>(<em>source</em>) is true, then <ol> <li>Return <em>"module"</em>.</li> </ol> </li> <li>Return <em>"commonjs"</em>.</li> </ol> </li> <li>Return <strong>undefined</strong> (will throw during load phase).</li> </ol> </blockquote> <p><strong>LOOKUP_PACKAGE_SCOPE</strong>(<em>url</em>)</p> <blockquote> <ol> <li>Let <em>scopeURL</em> be <em>url</em>.</li> <li>While <em>scopeURL</em> is not the file system root, <ol> <li>Set <em>scopeURL</em> to the parent URL of <em>scopeURL</em>.</li> <li>If <em>scopeURL</em> ends in a <em>"node_modules"</em> path segment, return <strong>null</strong>.</li> <li>Let <em>pjsonURL</em> be the resolution of <em>"package.json"</em> within <em>scopeURL</em>.</li> <li>if the file at <em>pjsonURL</em> exists, then <ol> <li>Return <em>scopeURL</em>.</li> </ol> </li> </ol> </li> <li>Return <strong>null</strong>.</li> </ol> </blockquote> <p><strong>READ_PACKAGE_JSON</strong>(<em>packageURL</em>)</p> <blockquote> <ol> <li>Let <em>pjsonURL</em> be the resolution of <em>"package.json"</em> within <em>packageURL</em>.</li> <li>If the file at <em>pjsonURL</em> does not exist, then <ol> <li>Return <strong>null</strong>.</li> </ol> </li> <li>If the file at <em>packageURL</em> does not parse as valid JSON, then <ol> <li>Throw an <em>Invalid Package Configuration</em> error.</li> </ol> </li> <li>Return the parsed JSON source of the file at <em>pjsonURL</em>.</li> </ol> </blockquote> <p><strong>DETECT_MODULE_SYNTAX</strong>(<em>source</em>)</p> <blockquote> <ol> <li>Parse <em>source</em> as an ECMAScript module.</li> <li>If the parse is successful, then <ol> <li>If <em>source</em> contains top-level <code>await</code>, static <code>import</code> or <code>export</code> statements, or <code>import.meta</code>, return <strong>true</strong>.</li> <li>If <em>source</em> contains a top-level lexical declaration (<code>const</code>, <code>let</code>, or <code>class</code>) of any of the CommonJS wrapper variables (<code>require</code>, <code>exports</code>, <code>module</code>, <code>__filename</code>, or <code>__dirname</code>) then return <strong>true</strong>.</li> </ol> </li> <li>Else return <strong>false</strong>.</li> </ol> </blockquote> </div><div> <h4>Customizing ESM specifier resolution algorithm<span><a class="mark" href="#customizing-esm-specifier-resolution-algorithm" id="customizing-esm-specifier-resolution-algorithm">#</a></span><a aria-hidden="true" class="legacy" id="esm_customizing_esm_specifier_resolution_algorithm"></a></h4> <p><a href="module.html#customization-hooks">Module customization hooks</a> provide a mechanism for customizing the ESM specifier resolution algorithm. An example that provides CommonJS-style resolution for ESM specifiers is <a href="https://github.com/nodejs/loaders-test/tree/main/commonjs-extension-resolution-loader">commonjs-extension-resolution-loader</a>.</p> <!-- Note: The cjs-module-lexer link should be kept in-sync with the deps version --></div></section> <!-- API END --> </div> </div> </div> </body> </html>