learnyounode

<!DOCTYPE html><html lang="en"><head> <meta charset="utf-8"> <meta name="viewport" content="width=device-width"> <title>ECMAScript Modules | Node.js v12.10.0 Documentation</title> <link rel="stylesheet" href="data:text/css;base64,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"> <link rel="stylesheet" href="data:text/css;base64,/*--------------------- Layout and Typography ----------------------------*/
html {
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* {
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body {
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h1 { font-size: 2.5rem }
h2 { font-size: 2rem }
h3 { font-size: 1.75rem }
h4 { font-size: 1.5rem }
h5 { font-size: 1.25rem }
h6 { font-size: 1rem }

h1, h2, h3, h4, h5, h6 {
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pre, tt, code, .pre, span.type, a.type {
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#content {
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a, a:link, a:active {
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  text-decoration: none;
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  padding: 1px 3px;
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a:hover, a:focus {
  color: #fff;
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}

strong {
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code a:hover {
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}

em code {
  font-style: normal;
}

#changelog #gtoc {
  display: none;
}

#gtoc {
  margin-top: .5rem;
  margin-bottom: 1rem;
}

#gtoc ul {
  list-style: none;
  margin-left: 0;
  line-height: 1.5rem;
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#gtoc > ul > li {
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  border-right: 1px #000 solid;
  margin-right: 0.4rem;
  padding-right: 0.4rem;
}

#gtoc > ul > li:last-child {
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  margin-right: 0;
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li.version-picker {
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li.version-picker:hover > a {
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}

li.version-picker:hover > ol {
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li.version-picker a span {
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ol.version-picker {
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  border: 1px #43853d solid;
  border-radius: 0 0 2px 2px;
  display: none;
  list-style: none;
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  right: 0;
  top: 1.25rem;
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#gtoc ol.version-picker li {
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ol.version-picker li a {
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ol.version-picker li:last-child a {
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.line {
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.api_stability {
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  font-family: "Lato", "Lucida Grande", "Lucida Sans Unicode", "Lucida Sans", Verdana, Tahoma, sans-serif;
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.api_stability * {
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.api_stability a {
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.api_stability a:hover, .api_stability a:active, .api_stability a:focus {
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.api_stability a code {
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.api_stability_0 {
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.api_stability_1 {
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.api_stability_2 {
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.api_metadata {
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.api_metadata span {
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ul.plain {
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abbr {
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p {
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}

#apicontent > *:last-child {
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  padding-bottom: 2rem;
}

table {
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  margin: 0 0 1.5rem 0;
}

th, td {
  border: 1px solid #aaa;
  padding: .75rem 1rem .75rem 1rem;
  vertical-align: top;
}

th {
  text-align:left;
}

ol, ul, dl {
  margin: 0 0 .6rem 0;
  padding: 0;
}

ol ul, ol ol, ol dl, ul ul, ul ol, ul dl, dl ul, dl ol, dl dl {
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}

ul, ol {
  margin-left: 2rem;
}

dl dt {
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}

dl dd {
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}

dd + dt.pre {
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}

#apicontent {
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}

#apicontent .line {
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}

h2 + h2 {
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}

h3 + h3 {
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h2, h3, h4, h5 {
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.srclink {
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h1 span, h2 span, h3 span, h4 span {
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h1 span:hover, h2 span:hover, h3 span:hover, h4 span:hover {
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h1 span a, h2 span a, h3 span a, h4 span a {
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pre, tt, code {
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}

.pre {
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pre {
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  vertical-align: top;
  background: #f2f2f2;
  margin: 1rem;
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}

pre > code {
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}

pre + h3 {
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code.pre {
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}

#intro {
  margin-top: 1.25rem;
  margin-left: 1rem;
}

#intro a {
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  font-weight: bold;
}

hr {
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  margin: 0 0 1rem 0;
}

#toc h2 {
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  margin: 1.5rem 0;
}

#toc p {
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#toc ul a {
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#toc ul li {
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}

#toc li > ul {
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}

#toc .stability_0::after {
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  color: #fff;
  content: "deprecated";
  margin-left: .25rem;
  padding: 1px 3px;
  border-radius: 3px;
}

#apicontent li {
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}

#apicontent li:last-child {
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}

tt, code {
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  background-color: #f2f2f2;
  border-radius: 2px;
  padding: 1px 3px;
}

.api_stability code {
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}

a code {
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  background: inherit;
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}

.type {
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}

#column1.interior {
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  padding: 0 2rem;
  -webkit-padding-start: 1.5rem;
}

#column2.interior {
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  background: #333;
  position: fixed;
  left: 0;
  top: 0;
  bottom: 0;
  overflow-x: hidden;
  overflow-y: scroll;
}

#column2 ul {
  list-style: none;
  margin: .9rem 0 .5rem;
  background: #333;
}

#column2 > :first-child {
  margin: 1.25rem;
  font-size: 1.5rem;
}

#column2 > ul:nth-child(2) {
  margin: 1.25rem 0 .5rem;
}

#column2 > ul:last-child {
  margin: .9rem 0 1.25rem;
}

#column2 ul li {
  padding-left: 1.25rem;
  margin-bottom: .5rem;
  padding-bottom: .5rem;
}

#column2 .line {
  margin: 0 .5rem;
  background-color: #707070;
}

#column2 ul li:last-child {
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}

#column2 ul li a {
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  border-radius: 0;
}

#column2 ul li a.active, #column2 ul li a.active:hover,
#column2 ul li a.active:focus {
  color: #43853d;
  border-radius: 0;
  border-bottom: 1px solid #43853d;
  background: none;
}

#intro a:hover, #intro a:focus,
#column2 ul li a:hover, #column2 ul li a:focus {
  color: #fff;
  background: none;
}

span > .mark, span > .mark:visited {
  color: #707070;
  position: absolute;
  top: 0px;
  right: 0px;
}

span > .mark:hover, span > .mark:focus, span > .mark:active {
  color: #43853d;
  background: none;
}

th > *:last-child, td > *:last-child {
  margin-bottom: 0;
}

.changelog > summary {
  margin: .5rem 0;
  padding: .5rem 0;
  cursor: pointer;
}

/* simpler clearfix */
.clearfix:after {
  content: ".";
  display: block;
  height: 0;
  clear: both;
  visibility: hidden;
}

.github_icon {
  vertical-align: middle;
  margin: -2px 3px 0 0;
}

@media only screen and (max-width: 1024px) {
  #content {
    overflow: visible;
  }
  #column1.interior {
    margin-left: 0;
    padding-left: .5rem;
    padding-right: .5rem;
    width: auto;
    overflow-y: visible;
  }
  #column2 {
    display: none;
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}

@media print {
  html {
    height: auto;
    font-size: 0.75em;
  }
  #column2.interior {
    display: none;
  }
  #column1.interior {
    margin-left: 0px;
    padding: 0px;
    overflow-y: auto;
  }
  .api_metadata,
  #toc,
  .srclink,
  #gtoc,
  .mark {
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  }
  h1 {
    font-size: 2rem;
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  h2 {
    font-size: 1.75rem;
  }
  h3 {
    font-size: 1.5rem;
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  h4 {
    font-size: 1.3rem;
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  h5 {
    font-size: 1.2rem;
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  h6 {
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  .api_stability {
    display: inline-block;
  }
  .api_stability a {
    text-decoration: none;
  }
  a {
    color: inherit;
  }
  #apicontent {
    overflow: hidden;
  }
}
"> <link rel="stylesheet" href="data:text/css;base64,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"> <link rel="canonical" href="https://nodejs.org/api/esm.html"> </head> <body class="alt apidoc" id="api-section-esm"> <div id="content" class="clearfix"> <div id="column2" class="interior"> <div id="intro" class="interior"> <a href="https://nodejs.org/" title="Go back to the home page"> Node.js </a> </div> <ul> <li><a href="https://nodejs.org/api/documentation.html" class="nav-documentation">About these Docs</a></li> <li><a href="https://nodejs.org/api/synopsis.html" class="nav-synopsis">Usage & Example</a></li> </ul> <div class="line"></div> <ul> <li><a href="https://nodejs.org/api/assert.html" class="nav-assert">Assertion Testing</a></li> <li><a href="https://nodejs.org/api/async_hooks.html" class="nav-async_hooks">Async Hooks</a></li> <li><a href="https://nodejs.org/api/buffer.html" class="nav-buffer">Buffer</a></li> <li><a href="https://nodejs.org/api/addons.html" class="nav-addons">C++ Addons</a></li> <li><a href="https://nodejs.org/api/n-api.html" class="nav-n-api">C/C++ Addons - N-API</a></li> <li><a href="https://nodejs.org/api/child_process.html" class="nav-child_process">Child Processes</a></li> <li><a href="https://nodejs.org/api/cluster.html" class="nav-cluster">Cluster</a></li> <li><a href="https://nodejs.org/api/cli.html" class="nav-cli">Command Line Options</a></li> <li><a href="https://nodejs.org/api/console.html" class="nav-console">Console</a></li> <li><a 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class="version-picker"> <a href="#">View another version <span>▼</span></a> <ol class="version-picker"><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 <b>LTS</b></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 <b>LTS</b></a></li></ol> </li> <li class="edit_on_github"><a href="https://github.com/nodejs/node/edit/master/doc/api/esm.md"><span class="github_icon"><svg height="16" width="16" viewBox="0 0 16.1 16.1" fill="currentColor"><path d="M8 0a8 8 0 0 0-2.5 15.6c.4 0 .5-.2.5-.4v-1.5c-2 .4-2.5-.5-2.7-1 0-.1-.5-.9-.8-1-.3-.2-.7-.6 0-.6.6 0 1 .6 1.2.8.7 1.2 1.9 1 2.4.7 0-.5.2-.9.5-1-1.8-.3-3.7-1-3.7-4 0-.9.3-1.6.8-2.2 0-.2-.3-1 .1-2 0 0 .7-.3 2.2.7a7.4 7.4 0 0 1 4 0c1.5-1 2.2-.8 2.2-.8.5 1.1.2 2 .1 2.1.5.6.8 1.3.8 2.2 0 3-1.9 3.7-3.6 4 .3.2.5.7.5 1.4v2.2c0 .2.1.5.5.4A8 8 0 0 0 16 8a8 8 0 0 0-8-8z"></path></svg></span>Edit on GitHub</a></li> </ul> </div> <hr> </header> <div id="toc"> <h2>Table of Contents</h2> <ul> <li> <p><span class="stability_1"><a href="#esm_ecmascript_modules">ECMAScript Modules</a></span></p> <ul> <li><a href="#esm_introduction">Introduction</a></li> <li><a href="#esm_enabling">Enabling</a></li> <li><a href="#esm_code_package_json_code_code_type_code_field"><code>package.json</code> <code>"type"</code> field</a></li> <li><a href="#esm_package_scope_and_file_extensions">Package Scope and File Extensions</a></li> <li><a href="#esm_code_input_type_code_flag"><code>--input-type</code> flag</a></li> <li><a href="#esm_package_entry_points">Package Entry Points</a></li> <li><a href="#esm_package_exports">Package Exports</a></li> <li> <p><a href="#esm_code_import_code_specifiers"><code>import</code> Specifiers</a></p> <ul> <li> <p><a href="#esm_terminology">Terminology</a></p> <ul> <li><a href="#esm_data_imports"><code>data:</code> Imports</a></li> </ul> </li> </ul> </li> <li><a href="#esm_import_meta">import.meta</a></li> <li> <p><a href="#esm_differences_between_es_modules_and_commonjs">Differences Between ES Modules and CommonJS</a></p> <ul> <li><a href="#esm_mandatory_file_extensions">Mandatory file extensions</a></li> <li><a href="#esm_no_code_node_path_code">No <code>NODE_PATH</code></a></li> <li><a href="#esm_no_code_require_code_code_exports_code_code_module_exports_code_code_filename_code_code_dirname_code">No <code>require</code>, <code>exports</code>, <code>module.exports</code>, <code>__filename</code>, <code>__dirname</code></a></li> <li><a href="#esm_no_code_require_extensions_code">No <code>require.extensions</code></a></li> <li><a href="#esm_no_code_require_cache_code">No <code>require.cache</code></a></li> <li><a href="#esm_url_based_paths">URL-based paths</a></li> </ul> </li> <li> <p><a href="#esm_interoperability_with_commonjs">Interoperability with CommonJS</a></p> <ul> <li><a href="#esm_code_require_code"><code>require</code></a></li> <li><a href="#esm_code_import_code_statements"><code>import</code> statements</a></li> <li><a href="#esm_code_import_code_expressions"><code>import()</code> expressions</a></li> </ul> </li> <li><a href="#esm_commonjs_json_and_native_modules">CommonJS, JSON, and Native Modules</a></li> <li><a href="#esm_builtin_modules">Builtin modules</a></li> <li><a href="#esm_json_modules">JSON Modules</a></li> <li><a href="#esm_experimental_wasm_modules">Experimental Wasm Modules</a></li> <li> <p><a href="#esm_experimental_loader_hooks">Experimental Loader hooks</a></p> <ul> <li><a href="#esm_resolve_hook">Resolve hook</a></li> <li><a href="#esm_dynamic_instantiate_hook">Dynamic instantiate hook</a></li> </ul> </li> <li> <p><a href="#esm_resolution_algorithm">Resolution Algorithm</a></p> <ul> <li><a href="#esm_features">Features</a></li> <li><a href="#esm_resolver_algorithm">Resolver Algorithm</a></li> <li><a href="#esm_customizing_esm_specifier_resolution_algorithm">Customizing ESM specifier resolution algorithm</a></li> </ul> </li> </ul> </li> </ul> </div> <div id="apicontent"> <h1>ECMAScript Modules<span><a class="mark" href="#esm_ecmascript_modules" id="esm_ecmascript_modules">#</a></span></h1> <p></p><div class="api_stability api_stability_1"><a href="https://nodejs.org/api/documentation.html#documentation_stability_index">Stability: 1</a> - Experimental</div><p></p> <h2>Introduction<span><a class="mark" href="#esm_introduction" id="esm_introduction">#</a></span></h2> <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>Node.js fully supports ECMAScript modules as they are currently specified and provides limited interoperability between them and the existing module format, <a href="https://nodejs.org/api/modules.html">CommonJS</a>.</p> <p>Node.js contains support for ES Modules based upon the <a href="https://github.com/nodejs/node-eps/blob/master/002-es-modules.md">Node.js EP for ES Modules</a> and the <a href="https://github.com/nodejs/modules/blob/master/doc/plan-for-new-modules-implementation.md">ECMAScript-modules implementation</a>.</p> <p>Expect major changes in the implementation including interoperability support, specifier resolution, and default behavior.</p> <h2>Enabling<span><a class="mark" href="#esm_enabling" id="esm_enabling">#</a></span></h2> <p>The <code>--experimental-modules</code> flag can be used to enable support for ECMAScript modules (ES modules).</p> <p>Once enabled, Node.js will treat the following as ES modules when passed to <code>node</code> as the initial input, or when referenced by <code>import</code> statements within ES module code:</p> <ul> <li> <p>Files ending in <code>.mjs</code>.</p> </li> <li> <p>Files ending in <code>.js</code>, or extensionless files, when the nearest parent <code>package.json</code> file contains a top-level field <code>"type"</code> with a value of <code>"module"</code>.</p> </li> <li> <p>Strings passed in as an argument to <code>--eval</code> or <code>--print</code>, or piped to <code>node</code> via <code>STDIN</code>, with the flag <code>--input-type=module</code>.</p> </li> </ul> <p>Node.js will treat as CommonJS all other forms of input, such as <code>.js</code> files where the nearest parent <code>package.json</code> file contains no top-level <code>"type"</code> field, or string input without the flag <code>--input-type</code>. This behavior is to preserve backward compatibility. However, now that Node.js supports both CommonJS and ES modules, it is best to be explicit whenever possible. Node.js will treat the following as CommonJS when passed to <code>node</code> as the initial input, or when referenced by <code>import</code> statements within ES module code:</p> <ul> <li> <p>Files ending in <code>.cjs</code>.</p> </li> <li> <p>Files ending in <code>.js</code>, or extensionless files, when the nearest parent <code>package.json</code> file contains a top-level field <code>"type"</code> with a value of <code>"commonjs"</code>.</p> </li> <li> <p>Strings passed in as an argument to <code>--eval</code> or <code>--print</code>, or piped to <code>node</code> via <code>STDIN</code>, with the flag <code>--input-type=commonjs</code>.</p> </li> </ul> <h2><code>package.json</code> <code>"type"</code> field<span><a class="mark" href="#esm_code_package_json_code_code_type_code_field" id="esm_code_package_json_code_code_type_code_field">#</a></span></h2> <p>Files ending with <code>.js</code> or <code>.mjs</code>, or lacking any extension, will be loaded as ES modules when the nearest parent <code>package.json</code> file contains a top-level field <code>"type"</code> with a value of <code>"module"</code>.</p> <p>The nearest parent <code>package.json</code> is defined as the first <code>package.json</code> found when searching in the current folder, that folder’s parent, and so on up until the root of the volume is reached.</p>  <pre><code class="language-js">// package.json { "type": "module" } </code></pre> <pre><code class="language-sh"># In same folder as above package.json node --experimental-modules my-app.js # Runs as ES module </code></pre> <p>If the nearest parent <code>package.json</code> lacks a <code>"type"</code> field, or contains <code>"type": "commonjs"</code>, extensionless and <code>.js</code> files are treated as CommonJS. If the volume root is reached and no <code>package.json</code> is found, Node.js defers to the default, a <code>package.json</code> with no <code>"type"</code> field.</p> <p><code>import</code> statements of <code>.js</code> and extensionless files are treated as ES modules if the nearest parent <code>package.json</code> contains <code>"type": "module"</code>.</p> <pre><code class="language-js">// my-app.js, part of the same example as above import './startup.js'; // Loaded as ES module because of package.json </code></pre> <h2>Package Scope and File Extensions<span><a class="mark" href="#esm_package_scope_and_file_extensions" id="esm_package_scope_and_file_extensions">#</a></span></h2> <p>A folder containing a <code>package.json</code> file, and all subfolders below that folder down until the next folder containing another <code>package.json</code>, is considered a <em>package scope</em>. The <code>"type"</code> field defines how <code>.js</code> and extensionless files should be treated within a particular <code>package.json</code> file’s package scope. Every package in a project’s <code>node_modules</code> folder contains its own <code>package.json</code> file, so each project’s dependencies have their own package scopes. A <code>package.json</code> lacking a <code>"type"</code> field is treated as if it contained <code>"type": "commonjs"</code>.</p> <p>The package scope applies not only to initial entry points (<code>node --experimental-modules my-app.js</code>) but also to files referenced by <code>import</code> statements and <code>import()</code> expressions.</p> <pre><code class="language-js">// my-app.js, in an ES module package scope because there is a package.json // file in the same folder with "type": "module". import './startup/init.js'; // Loaded as ES module since ./startup contains no package.json file, // and therefore inherits the ES module package scope from one level up. import 'commonjs-package'; // Loaded as CommonJS since ./node_modules/commonjs-package/package.json // lacks a "type" field or contains "type": "commonjs". import './node_modules/commonjs-package/index.js'; // Loaded as CommonJS since ./node_modules/commonjs-package/package.json // lacks a "type" field or contains "type": "commonjs". </code></pre> <p>Files ending with <code>.mjs</code> are always loaded as ES modules regardless of package scope.</p> <p>Files ending with <code>.cjs</code> are always loaded as CommonJS regardless of package scope.</p> <pre><code class="language-js">import './legacy-file.cjs'; // Loaded as CommonJS since .cjs is always loaded as CommonJS. import 'commonjs-package/src/index.mjs'; // Loaded as ES module since .mjs is always loaded as ES module. </code></pre> <p>The <code>.mjs</code> and <code>.cjs</code> extensions may be used to mix types within the same package scope:</p> <ul> <li> <p>Within a <code>"type": "module"</code> package scope, Node.js can be instructed to interpret a particular file as CommonJS by naming it with a <code>.cjs</code> extension (since both <code>.js</code> and <code>.mjs</code> files are treated as ES modules within a <code>"module"</code> package scope).</p> </li> <li> <p>Within a <code>"type": "commonjs"</code> package scope, Node.js can be instructed to interpret a particular file as an ES module by naming it with an <code>.mjs</code> extension (since both <code>.js</code> and <code>.cjs</code> files are treated as CommonJS within a <code>"commonjs"</code> package scope).</p> </li> </ul> <h2><code>--input-type</code> flag<span><a class="mark" href="#esm_code_input_type_code_flag" id="esm_code_input_type_code_flag">#</a></span></h2> <p>Strings passed in as an argument to <code>--eval</code> or <code>--print</code> (or <code>-e</code> or <code>-p</code>), or piped to <code>node</code> via <code>STDIN</code>, will be treated as ES modules when the <code>--input-type=module</code> flag is set.</p> <pre><code class="language-sh">node --experimental-modules --input-type=module --eval \ "import { sep } from 'path'; console.log(sep);" echo "import { sep } from 'path'; console.log(sep);" | \ node --experimental-modules --input-type=module </code></pre> <p>For completeness there is also <code>--input-type=commonjs</code>, for explicitly running string input as CommonJS. This is the default behavior if <code>--input-type</code> is unspecified.</p> <h2>Package Entry Points<span><a class="mark" href="#esm_package_entry_points" id="esm_package_entry_points">#</a></span></h2> <p>The <code>package.json</code> <code>"main"</code> field defines the entry point for a package, whether the package is included into CommonJS via <code>require</code> or into an ES module via <code>import</code>.</p>  <pre><code class="language-js">// ./node_modules/es-module-package/package.json { "type": "module", "main": "./src/index.js" } </code></pre> <pre><code class="language-js">// ./my-app.mjs import { something } from 'es-module-package'; // Loads from ./node_modules/es-module-package/src/index.js </code></pre> <p>An attempt to <code>require</code> the above <code>es-module-package</code> would attempt to load <code>./node_modules/es-module-package/src/index.js</code> as CommonJS, which would throw an error as Node.js would not be able to parse the <code>export</code> statement in CommonJS.</p> <p>As with <code>import</code> statements, for ES module usage the value of <code>"main"</code> must be a full path including extension: <code>"./index.mjs"</code>, not <code>"./index"</code>.</p> <p>If the <code>package.json</code> <code>"type"</code> field is omitted, a <code>.js</code> file in <code>"main"</code> will be interpreted as CommonJS.</p> <p>The <code>"main"</code> field can point to exactly one file, regardless of whether the package is referenced via <code>require</code> (in a CommonJS context) or <code>import</code> (in an ES module context). Package authors who want to publish a package to be used in both contexts can do so by setting <code>"main"</code> to point to the CommonJS entry point and informing the package’s users of the path to the ES module entry point. Such a package would be accessible like <code>require('pkg')</code> and <code>import 'pkg/module.mjs'</code>. Alternatively the package <code>"main"</code> could point to the ES module entry point and legacy users could be informed of the CommonJS entry point path, e.g. <code>require('pkg/commonjs')</code>.</p> <h2>Package Exports<span><a class="mark" href="#esm_package_exports" id="esm_package_exports">#</a></span></h2> <p>By default, all subpaths from a package can be imported (<code>import 'pkg/x.js'</code>). Custom subpath aliasing and encapsulation can be provided through the <code>"exports"</code> field.</p>  <pre><code class="language-js">// ./node_modules/es-module-package/package.json { "exports": { "./submodule": "./src/submodule.js" } } </code></pre> <pre><code class="language-js">import submodule from 'es-module-package/submodule'; // Loads ./node_modules/es-module-package/src/submodule.js </code></pre> <p>In addition to defining an alias, subpaths not defined by <code>"exports"</code> will throw when an attempt is made to import them:</p> <pre><code class="language-js">import submodule from 'es-module-package/private-module.js'; // Throws - Module not found </code></pre> <blockquote> <p>Note: this is not a strong encapsulation as any private modules can still be loaded by absolute paths.</p> </blockquote> <p>Folders can also be mapped with package exports:</p>  <pre><code class="language-js">// ./node_modules/es-module-package/package.json { "exports": { "./features/": "./src/features/" } } </code></pre> <pre><code class="language-js">import feature from 'es-module-package/features/x.js'; // Loads ./node_modules/es-module-package/src/features/x.js </code></pre> <p>If a package has no exports, setting <code>"exports": false</code> can be used instead of <code>"exports": {}</code> to indicate the package does not intend for submodules to be exposed.</p> <p>Any invalid exports entries will be ignored. This includes exports not starting with <code>"./"</code> or a missing trailing <code>"/"</code> for directory exports.</p> <p>Array fallback support is provided for exports, similarly to import maps in order to be forward-compatible with fallback workflows in future:</p>  <pre><code class="language-js">{ "exports": { "./submodule": ["not:valid", "./submodule.js"] } } </code></pre> <p>Since <code>"not:valid"</code> is not a supported target, <code>"./submodule.js"</code> is used instead as the fallback, as if it were the only target.</p> <h2><code>import</code> Specifiers<span><a class="mark" href="#esm_code_import_code_specifiers" id="esm_code_import_code_specifiers">#</a></span></h2> <h3>Terminology<span><a class="mark" href="#esm_terminology" id="esm_terminology">#</a></span></h3> <p>The <em>specifier</em> of an <code>import</code> statement is the string after the <code>from</code> keyword, e.g. <code>'path'</code> in <code>import { sep } from '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 four types of specifiers:</p> <ul> <li> <p><em>Bare specifiers</em> like <code>'some-package'</code>. They refer to an entry point of a package by the package name.</p> </li> <li> <p><em>Deep import specifiers</em> like <code>'some-package/lib/shuffle.mjs'</code>. They refer to a path within a package prefixed by the package name.</p> </li> <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.</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 specifiers, and the bare specifier portion of deep import specifiers, are strings; but everything else in a specifier is a URL.</p> <p>Only <code>file:</code> and <code>data:</code> URLs are supported. A specifier like <code>'https://example.com/app.js'</code> may be supported by browsers but it is not supported in Node.js.</p> <p>Specifiers may not begin with <code>/</code> or <code>//</code>. These are reserved for potential future use. The root of the current volume may be referenced via <code>file:///</code>.</p> <h4><code>data:</code> Imports<span><a class="mark" href="#esm_data_imports" id="esm_data_imports">#</a></span></h4> <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> <p><code>data:</code> URLs only resolve <a href="#esm_terminology"><em>Bare specifiers</em></a> for builtin modules and <a href="#esm_terminology"><em>Absolute specifiers</em></a>. Resolving <a href="#esm_terminology"><em>Relative specifiers</em></a> will 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> will fail to resolve since there is no concept of relative resolution for <code>data:</code> URLs. An example of a <code>data:</code> URLs being used is:</p> <pre><code class="language-js">import 'data:text/javascript,console.log("hello!");'; import _ from 'data:application/json,"world!"'; </code></pre> <h2>import.meta<span><a class="mark" href="#esm_import_meta" id="esm_import_meta">#</a></span></h2> <ul> <li><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> metaproperty is an <code>Object</code> that contains the following property:</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 absolute <code>file:</code> URL of the module.</li> </ul> <h2>Differences Between ES Modules and CommonJS<span><a class="mark" href="#esm_differences_between_es_modules_and_commonjs" id="esm_differences_between_es_modules_and_commonjs">#</a></span></h2> <h3>Mandatory file extensions<span><a class="mark" href="#esm_mandatory_file_extensions" id="esm_mandatory_file_extensions">#</a></span></h3> <p>A file extension must be provided when using the <code>import</code> keyword. 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> <h3>No <code>NODE_PATH</code><span><a class="mark" href="#esm_no_code_node_path_code" id="esm_no_code_node_path_code">#</a></span></h3> <p><code>NODE_PATH</code> is not part of resolving <code>import</code> specifiers. Please use symlinks if this behavior is desired.</p> <h3>No <code>require</code>, <code>exports</code>, <code>module.exports</code>, <code>__filename</code>, <code>__dirname</code><span><a class="mark" href="#esm_no_code_require_code_code_exports_code_code_module_exports_code_code_filename_code_code_dirname_code" id="esm_no_code_require_code_code_exports_code_code_module_exports_code_code_filename_code_code_dirname_code">#</a></span></h3> <p>These CommonJS variables are not available in ES modules.</p> <p><code>require</code> can be imported into an ES module using <a href="https://nodejs.org/api/modules.html#modules_module_createrequire_filename"><code>module.createRequire()</code></a>.</p> <p>Equivalents of <code>__filename</code> and <code>__dirname</code> can be created inside of each file via <a href="#esm_import_meta"><code>import.meta.url</code></a>.</p> <pre><code class="language-js">import { fileURLToPath } from 'url'; import { dirname } from 'path'; const __filename = fileURLToPath(import.meta.url); const __dirname = dirname(__filename); </code></pre> <h3>No <code>require.extensions</code><span><a class="mark" href="#esm_no_code_require_extensions_code" id="esm_no_code_require_extensions_code">#</a></span></h3> <p><code>require.extensions</code> is not used by <code>import</code>. The expectation is that loader hooks can provide this workflow in the future.</p> <h3>No <code>require.cache</code><span><a class="mark" href="#esm_no_code_require_cache_code" id="esm_no_code_require_cache_code">#</a></span></h3> <p><code>require.cache</code> is not used by <code>import</code>. It has a separate cache.</p> <h3>URL-based paths<span><a class="mark" href="#esm_url_based_paths" id="esm_url_based_paths">#</a></span></h3> <p>ES modules are resolved and cached based upon <a href="https://url.spec.whatwg.org/">URL</a> semantics. This means that files containing special characters such as <code>#</code> and <code>?</code> need to be escaped.</p> <p>Modules will be loaded multiple times if the <code>import</code> specifier used to resolve them have a different query or fragment.</p> <pre><code class="language-js">import './foo.mjs?query=1'; // loads ./foo.mjs with query of "?query=1" import './foo.mjs?query=2'; // loads ./foo.mjs with query of "?query=2" </code></pre> <p>For now, only modules using the <code>file:</code> protocol can be loaded.</p> <h2>Interoperability with CommonJS<span><a class="mark" href="#esm_interoperability_with_commonjs" id="esm_interoperability_with_commonjs">#</a></span></h2> <h3><code>require</code><span><a class="mark" href="#esm_code_require_code" id="esm_code_require_code">#</a></span></h3> <p><code>require</code> always treats the files it references as CommonJS. This applies whether <code>require</code> is used the traditional way within a CommonJS environment, or in an ES module environment using <a href="https://nodejs.org/api/modules.html#modules_module_createrequire_filename"><code>module.createRequire()</code></a>.</p> <p>To include an ES module into CommonJS, use <a href="#esm_import-expressions"><code>import()</code></a>.</p> <h3><code>import</code> statements<span><a class="mark" href="#esm_code_import_code_statements" id="esm_code_import_code_statements">#</a></span></h3> <p>An <code>import</code> statement can reference an ES module, a CommonJS module, or JSON. Other file types such as Native modules are not supported. For those, use <a href="https://nodejs.org/api/modules.html#modules_module_createrequire_filename"><code>module.createRequire()</code></a>.</p> <p><code>import</code> statements are permitted only in ES modules. For similar functionality in CommonJS, see <a href="#esm_import-expressions"><code>import()</code></a>.</p> <p>The <em>specifier</em> of an <code>import</code> statement (the string after the <code>from</code> keyword) can either be an URL-style relative path like <code>'./file.mjs'</code> or a package name like <code>'fs'</code>.</p> <p>Like in CommonJS, files within packages can be accessed by appending a path to the package name.</p> <pre><code class="language-js">import { sin, cos } from 'geometry/trigonometry-functions.mjs'; </code></pre> <blockquote> <p>Currently only the “default export” is supported for CommonJS files or packages:</p>  <pre><code class="language-js">import packageMain from 'commonjs-package'; // Works import { method } from 'commonjs-package'; // Errors </code></pre> <p>There are ongoing efforts to make the latter code possible.</p> </blockquote> <h3><code>import()</code> expressions<span><a class="mark" href="#esm_code_import_code_expressions" id="esm_code_import_code_expressions">#</a></span></h3> <p>Dynamic <code>import()</code> is supported in both CommonJS and ES modules. It can be used to include ES module files from CommonJS code.</p> <pre><code class="language-js">(async () => { await import('./my-app.mjs'); })(); </code></pre> <h2>CommonJS, JSON, and Native Modules<span><a class="mark" href="#esm_commonjs_json_and_native_modules" id="esm_commonjs_json_and_native_modules">#</a></span></h2> <p>CommonJS, JSON, and Native modules can be used with <a href="https://nodejs.org/api/modules.html#modules_module_createrequire_filename"><code>module.createRequire()</code></a>.</p> <pre><code class="language-js">// cjs.js module.exports = 'cjs'; // esm.mjs import { createRequire } from 'module'; import { fileURLToPath as fromURL } from 'url'; const require = createRequire(fromURL(import.meta.url)); const cjs = require('./cjs'); cjs === 'cjs'; // true </code></pre> <h2>Builtin modules<span><a class="mark" href="#esm_builtin_modules" id="esm_builtin_modules">#</a></span></h2> <p>Builtin modules will provide named exports of their public API, as well as a default export which can be used for, among other things, modifying the named exports. Named exports of builtin modules are updated when the corresponding exports property is accessed, redefined, or deleted.</p> <pre><code class="language-js">import EventEmitter from 'events'; const e = new EventEmitter(); </code></pre> <pre><code class="language-js">import { readFile } from 'fs'; readFile('./foo.txt', (err, source) => { if (err) { console.error(err); } else { console.log(source); } }); </code></pre> <pre><code class="language-js">import fs, { readFileSync } from 'fs'; fs.readFileSync = () => Buffer.from('Hello, ESM'); fs.readFileSync === readFileSync; </code></pre> <h2>JSON Modules<span><a class="mark" href="#esm_json_modules" id="esm_json_modules">#</a></span></h2> <p>JSON modules follow the <a href="https://html.spec.whatwg.org/#creating-a-json-module-script">WHATWG JSON modules specification</a>.</p> <p>The imported JSON only exposes a <code>default</code>. There is no support for named exports. A cache entry is created in the CommonJS cache, to avoid duplication. The same object will be returned in CommonJS if the JSON module has already been imported from the same path.</p> <p>Assuming