1<!DOCTYPE html> 2<html lang="en"> 3<head> 4 <meta charset="utf-8"> 5 <meta name="viewport" content="width=device-width"> 6 <meta name="nodejs.org:node-version" content="v14.20.1"> 7 <title>Modules: Packages | Node.js v14.20.1 Documentation</title> 8 <link rel="stylesheet" href="https://fonts.googleapis.com/css?family=Lato:400,700,400italic&display=fallback"> 9 <link rel="stylesheet" href="assets/style.css"> 10 <link rel="stylesheet" href="assets/hljs.css"> 11 <link rel="canonical" href="https://nodejs.org/api/packages.html"> 12</head> 13<body class="alt apidoc" id="api-section-packages"> 14 <div id="content" class="clearfix"> 15 <div id="column2" class="interior"> 16 <div id="intro" class="interior"> 17 <a href="/" title="Go back to the home page"> 18 Node.js 19 </a> 20 </div> 21 <ul> 22<li><a href="documentation.html" class="nav-documentation">About this documentation</a></li> 23<li><a href="synopsis.html" class="nav-synopsis">Usage and example</a></li> 24</ul> 25<hr class="line"> 26<ul> 27<li><a href="assert.html" class="nav-assert">Assertion testing</a></li> 28<li><a href="async_hooks.html" class="nav-async_hooks">Async hooks</a></li> 29<li><a href="buffer.html" class="nav-buffer">Buffer</a></li> 30<li><a href="addons.html" class="nav-addons">C++ addons</a></li> 31<li><a href="n-api.html" class="nav-n-api">C/C++ addons with Node-API</a></li> 32<li><a href="embedding.html" class="nav-embedding">C++ embedder API</a></li> 33<li><a href="child_process.html" class="nav-child_process">Child processes</a></li> 34<li><a href="cluster.html" class="nav-cluster">Cluster</a></li> 35<li><a href="cli.html" class="nav-cli">Command-line options</a></li> 36<li><a href="console.html" class="nav-console">Console</a></li> 37<li><a href="corepack.html" class="nav-corepack">Corepack</a></li> 38<li><a href="crypto.html" class="nav-crypto">Crypto</a></li> 39<li><a href="debugger.html" class="nav-debugger">Debugger</a></li> 40<li><a href="deprecations.html" class="nav-deprecations">Deprecated APIs</a></li> 41<li><a href="diagnostics_channel.html" class="nav-diagnostics_channel">Diagnostics Channel</a></li> 42<li><a href="dns.html" class="nav-dns">DNS</a></li> 43<li><a href="domain.html" class="nav-domain">Domain</a></li> 44<li><a href="errors.html" class="nav-errors">Errors</a></li> 45<li><a href="events.html" class="nav-events">Events</a></li> 46<li><a href="fs.html" class="nav-fs">File system</a></li> 47<li><a href="globals.html" class="nav-globals">Globals</a></li> 48<li><a href="http.html" class="nav-http">HTTP</a></li> 49<li><a href="http2.html" class="nav-http2">HTTP/2</a></li> 50<li><a href="https.html" class="nav-https">HTTPS</a></li> 51<li><a href="inspector.html" class="nav-inspector">Inspector</a></li> 52<li><a href="intl.html" class="nav-intl">Internationalization</a></li> 53<li><a href="modules.html" class="nav-modules">Modules: CommonJS modules</a></li> 54<li><a href="esm.html" class="nav-esm">Modules: ECMAScript modules</a></li> 55<li><a href="module.html" class="nav-module">Modules: <code>module</code> API</a></li> 56<li><a href="packages.html" class="nav-packages active">Modules: Packages</a></li> 57<li><a href="net.html" class="nav-net">Net</a></li> 58<li><a href="os.html" class="nav-os">OS</a></li> 59<li><a href="path.html" class="nav-path">Path</a></li> 60<li><a href="perf_hooks.html" class="nav-perf_hooks">Performance hooks</a></li> 61<li><a href="policy.html" class="nav-policy">Policies</a></li> 62<li><a href="process.html" class="nav-process">Process</a></li> 63<li><a href="punycode.html" class="nav-punycode">Punycode</a></li> 64<li><a href="querystring.html" class="nav-querystring">Query strings</a></li> 65<li><a href="readline.html" class="nav-readline">Readline</a></li> 66<li><a href="repl.html" class="nav-repl">REPL</a></li> 67<li><a href="report.html" class="nav-report">Report</a></li> 68<li><a href="stream.html" class="nav-stream">Stream</a></li> 69<li><a href="string_decoder.html" class="nav-string_decoder">String decoder</a></li> 70<li><a href="timers.html" class="nav-timers">Timers</a></li> 71<li><a href="tls.html" class="nav-tls">TLS/SSL</a></li> 72<li><a href="tracing.html" class="nav-tracing">Trace events</a></li> 73<li><a href="tty.html" class="nav-tty">TTY</a></li> 74<li><a href="dgram.html" class="nav-dgram">UDP/datagram</a></li> 75<li><a href="url.html" class="nav-url">URL</a></li> 76<li><a href="util.html" class="nav-util">Utilities</a></li> 77<li><a href="v8.html" class="nav-v8">V8</a></li> 78<li><a href="vm.html" class="nav-vm">VM</a></li> 79<li><a href="wasi.html" class="nav-wasi">WASI</a></li> 80<li><a href="worker_threads.html" class="nav-worker_threads">Worker threads</a></li> 81<li><a href="zlib.html" class="nav-zlib">Zlib</a></li> 82</ul> 83<hr class="line"> 84<ul> 85<li><a href="https://github.com/nodejs/node" class="nav-https-github-com-nodejs-node">Code repository and issue tracker</a></li> 86</ul> 87 </div> 88 89 <div id="column1" data-id="packages" class="interior"> 90 <header> 91 <div class="header-container"> 92 <h1>Node.js v14.20.1 documentation</h1> 93 <button class="theme-toggle-btn" id="theme-toggle-btn" title="Toggle dark mode/light mode" aria-label="Toggle dark mode/light mode" hidden> 94 <svg xmlns="http://www.w3.org/2000/svg" class="icon dark-icon" height="24" width="24"> 95 <path fill="none" d="M0 0h24v24H0z" /> 96 <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"/> 97 <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"/> 98 </svg> 99 <svg xmlns="http://www.w3.org/2000/svg" class="icon light-icon" height="24" width="24"> 100 <path d="M0 0h24v24H0z" fill="none" /> 101 <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"/> 102 </svg> 103 </button> 104 </div> 105 <div id="gtoc"> 106 <ul> 107 <li> 108 <a href="index.html">Index</a> 109 </li> 110 <li> 111 <a href="all.html">View on single page</a> 112 </li> 113 <li> 114 <a href="packages.json">View as JSON</a> 115 </li> 116 117 <li class="version-picker"> 118 <a href="#">View another version <span>▼</span></a> 119 <ol class="version-picker"><li><a href="https://nodejs.org/docs/latest-v18.x/api/packages.html">18.x</a></li> 120<li><a href="https://nodejs.org/docs/latest-v17.x/api/packages.html">17.x</a></li> 121<li><a href="https://nodejs.org/docs/latest-v16.x/api/packages.html">16.x <b>LTS</b></a></li> 122<li><a href="https://nodejs.org/docs/latest-v15.x/api/packages.html">15.x</a></li> 123<li><a href="https://nodejs.org/docs/latest-v14.x/api/packages.html">14.x <b>LTS</b></a></li> 124<li><a href="https://nodejs.org/docs/latest-v13.x/api/packages.html">13.x</a></li> 125<li><a href="https://nodejs.org/docs/latest-v12.x/api/packages.html">12.x <b>LTS</b></a></li></ol> 126 </li> 127 128 <li class="edit_on_github"><a href="https://github.com/nodejs/node/edit/master/doc/api/packages.md">Edit on GitHub</a></li> 129 </ul> 130 </div> 131 <hr> 132 </header> 133 134 <details id="toc" open><summary>Table of contents</summary><ul> 135<li><a href="#packages_modules_packages">Modules: Packages</a> 136<ul> 137<li><a href="#packages_introduction">Introduction</a></li> 138<li><a href="#packages_determining_module_system">Determining module system</a> 139<ul> 140<li><a href="#packages_package_json_and_file_extensions"><code>package.json</code> and file extensions</a></li> 141<li><a href="#packages_input_type_flag"><code>--input-type</code> flag</a></li> 142</ul> 143</li> 144<li><span class="stability_1"><a href="#packages_determining_package_manager">Determining package manager</a></span></li> 145<li><a href="#packages_package_entry_points">Package entry points</a> 146<ul> 147<li><a href="#packages_main_entry_point_export">Main entry point export</a></li> 148<li><a href="#packages_subpath_exports">Subpath exports</a></li> 149<li><a href="#packages_subpath_imports">Subpath imports</a></li> 150<li><a href="#packages_subpath_patterns">Subpath patterns</a></li> 151<li><a href="#packages_exports_sugar">Exports sugar</a></li> 152<li><a href="#packages_conditional_exports">Conditional exports</a></li> 153<li><a href="#packages_nested_conditions">Nested conditions</a></li> 154<li><a href="#packages_resolving_user_conditions">Resolving user conditions</a></li> 155<li><a href="#packages_conditions_definitions">Conditions Definitions</a></li> 156<li><a href="#packages_self_referencing_a_package_using_its_name">Self-referencing a package using its name</a></li> 157</ul> 158</li> 159<li><a href="#packages_dual_commonjs_es_module_packages">Dual CommonJS/ES module packages</a> 160<ul> 161<li><a href="#packages_dual_package_hazard">Dual package hazard</a></li> 162<li><a href="#packages_writing_dual_packages_while_avoiding_or_minimizing_hazards">Writing dual packages while avoiding or minimizing hazards</a> 163<ul> 164<li><a href="#packages_approach_1_use_an_es_module_wrapper">Approach #1: Use an ES module wrapper</a></li> 165<li><a href="#packages_approach_2_isolate_state">Approach #2: Isolate state</a></li> 166</ul> 167</li> 168</ul> 169</li> 170<li><a href="#packages_node_js_package_json_field_definitions">Node.js <code>package.json</code> field definitions</a> 171<ul> 172<li><a href="#packages_name"><code>"name"</code></a></li> 173<li><a href="#packages_main"><code>"main"</code></a></li> 174<li><span class="stability_1"><a href="#packages_packagemanager"><code>"packageManager"</code></a></span></li> 175<li><a href="#packages_type"><code>"type"</code></a></li> 176<li><a href="#packages_exports"><code>"exports"</code></a></li> 177<li><a href="#packages_imports"><code>"imports"</code></a></li> 178</ul> 179</li> 180</ul> 181</li> 182</ul></details> 183 184 <div id="apicontent"> 185 <h2>Modules: Packages<span><a class="mark" href="#packages_modules_packages" id="packages_modules_packages">#</a></span></h2> 186 187 188<div class="api_metadata"> 189<details class="changelog"><summary>History</summary> 190<table> 191<tbody><tr><th>Version</th><th>Changes</th></tr> 192<tr><td>v14.13.0</td> 193<td><p>Add support for <code>"exports"</code> patterns.</p></td></tr> 194<tr><td>v14.6.0, v12.19.0</td> 195<td><p>Add package <code>"imports"</code> field.</p></td></tr> 196<tr><td>v13.7.0, v12.16.0</td> 197<td><p>Unflag conditional exports.</p></td></tr> 198<tr><td>v13.6.0, v12.16.0</td> 199<td><p>Unflag self-referencing a package using its name.</p></td></tr> 200<tr><td>v12.7.0</td> 201<td><p>Introduce <code>"exports"</code> <code>package.json</code> field as a more powerful alternative to the classic <code>"main"</code> field.</p></td></tr> 202<tr><td>v12.0.0</td> 203<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> 204</tbody></table> 205</details> 206</div> 207<section><h3>Introduction<span><a class="mark" href="#packages_introduction" id="packages_introduction">#</a></span></h3> 208<p>A package is a folder tree described by a <code>package.json</code> file. The package 209consists of the folder containing the <code>package.json</code> file and all subfolders 210until the next folder containing another <code>package.json</code> file, or a folder 211named <code>node_modules</code>.</p> 212<p>This page provides guidance for package authors writing <code>package.json</code> files 213along with a reference for the <a href="#packages_node_js_package_json_field_definitions"><code>package.json</code></a> fields defined by Node.js.</p> 214</section><section><h3>Determining module system<span><a class="mark" href="#packages_determining_module_system" id="packages_determining_module_system">#</a></span></h3> 215<p>Node.js will treat the following as <a href="esm.html">ES modules</a> when passed to <code>node</code> as the 216initial input, or when referenced by <code>import</code> statements within ES module code:</p> 217<ul> 218<li> 219<p>Files ending in <code>.mjs</code>.</p> 220</li> 221<li> 222<p>Files ending in <code>.js</code> when the nearest parent <code>package.json</code> file contains a 223top-level <a href="#packages_type"><code>"type"</code></a> field with a value of <code>"module"</code>.</p> 224</li> 225<li> 226<p>Strings passed in as an argument to <code>--eval</code>, or piped to <code>node</code> via <code>STDIN</code>, 227with the flag <code>--input-type=module</code>.</p> 228</li> 229</ul> 230<p>Node.js will treat as <a href="modules.html">CommonJS</a> all other forms of input, such as <code>.js</code> files 231where the nearest parent <code>package.json</code> file contains no top-level <code>"type"</code> 232field, or string input without the flag <code>--input-type</code>. This behavior is to 233preserve backward compatibility. However, now that Node.js supports both 234CommonJS and ES modules, it is best to be explicit whenever possible. Node.js 235will treat the following as CommonJS when passed to <code>node</code> as the initial input, 236or when referenced by <code>import</code> statements within ES module code:</p> 237<ul> 238<li> 239<p>Files ending in <code>.cjs</code>.</p> 240</li> 241<li> 242<p>Files ending in <code>.js</code> when the nearest parent <code>package.json</code> file contains a 243top-level field <a href="#packages_type"><code>"type"</code></a> with a value of <code>"commonjs"</code>.</p> 244</li> 245<li> 246<p>Strings passed in as an argument to <code>--eval</code> or <code>--print</code>, or piped to <code>node</code> 247via <code>STDIN</code>, with the flag <code>--input-type=commonjs</code>.</p> 248</li> 249</ul> 250<p>Package authors should include the <a href="#packages_type"><code>"type"</code></a> field, even in packages where 251all sources are CommonJS. Being explicit about the <code>type</code> of the package will 252future-proof the package in case the default type of Node.js ever changes, and 253it will also make things easier for build tools and loaders to determine how the 254files in the package should be interpreted.</p> 255<h4><code>package.json</code> and file extensions<span><a class="mark" href="#packages_package_json_and_file_extensions" id="packages_package_json_and_file_extensions">#</a></span></h4> 256<p>Within a package, the <a href="#packages_node_js_package_json_field_definitions"><code>package.json</code></a> <a href="#packages_type"><code>"type"</code></a> field defines how 257Node.js should interpret <code>.js</code> files. If a <code>package.json</code> file does not have a 258<code>"type"</code> field, <code>.js</code> files are treated as <a href="modules.html">CommonJS</a>.</p> 259<p>A <code>package.json</code> <code>"type"</code> value of <code>"module"</code> tells Node.js to interpret <code>.js</code> 260files within that package as using <a href="esm.html">ES module</a> syntax.</p> 261<p>The <code>"type"</code> field applies not only to initial entry points (<code>node my-app.js</code>) 262but also to files referenced by <code>import</code> statements and <code>import()</code> expressions.</p> 263<pre><code class="language-js"><span class="hljs-comment">// my-app.js, treated as an ES module because there is a package.json</span> 264<span class="hljs-comment">// file in the same folder with "type": "module".</span> 265 266<span class="hljs-keyword">import</span> <span class="hljs-string">'./startup/init.js'</span>; 267<span class="hljs-comment">// Loaded as ES module since ./startup contains no package.json file,</span> 268<span class="hljs-comment">// and therefore inherits the "type" value from one level up.</span> 269 270<span class="hljs-keyword">import</span> <span class="hljs-string">'commonjs-package'</span>; 271<span class="hljs-comment">// Loaded as CommonJS since ./node_modules/commonjs-package/package.json</span> 272<span class="hljs-comment">// lacks a "type" field or contains "type": "commonjs".</span> 273 274<span class="hljs-keyword">import</span> <span class="hljs-string">'./node_modules/commonjs-package/index.js'</span>; 275<span class="hljs-comment">// Loaded as CommonJS since ./node_modules/commonjs-package/package.json</span> 276<span class="hljs-comment">// lacks a "type" field or contains "type": "commonjs".</span></code></pre> 277<p>Files ending with <code>.mjs</code> are always loaded as <a href="esm.html">ES modules</a> regardless of 278the nearest parent <code>package.json</code>.</p> 279<p>Files ending with <code>.cjs</code> are always loaded as <a href="modules.html">CommonJS</a> regardless of the 280nearest parent <code>package.json</code>.</p> 281<pre><code class="language-js"><span class="hljs-keyword">import</span> <span class="hljs-string">'./legacy-file.cjs'</span>; 282<span class="hljs-comment">// Loaded as CommonJS since .cjs is always loaded as CommonJS.</span> 283 284<span class="hljs-keyword">import</span> <span class="hljs-string">'commonjs-package/src/index.mjs'</span>; 285<span class="hljs-comment">// Loaded as ES module since .mjs is always loaded as ES module.</span></code></pre> 286<p>The <code>.mjs</code> and <code>.cjs</code> extensions can be used to mix types within the same 287package:</p> 288<ul> 289<li> 290<p>Within a <code>"type": "module"</code> package, Node.js can be instructed to 291interpret a particular file as <a href="modules.html">CommonJS</a> by naming it with a <code>.cjs</code> 292extension (since both <code>.js</code> and <code>.mjs</code> files are treated as ES modules within 293a <code>"module"</code> package).</p> 294</li> 295<li> 296<p>Within a <code>"type": "commonjs"</code> package, Node.js can be instructed to 297interpret a particular file as an <a href="esm.html">ES module</a> by naming it with an <code>.mjs</code> 298extension (since both <code>.js</code> and <code>.cjs</code> files are treated as CommonJS within a 299<code>"commonjs"</code> package).</p> 300</li> 301</ul> 302<h4><code>--input-type</code> flag<span><a class="mark" href="#packages_input_type_flag" id="packages_input_type_flag">#</a></span></h4> 303<div class="api_metadata"> 304<span>Added in: v12.0.0</span> 305</div> 306<p>Strings passed in as an argument to <code>--eval</code> (or <code>-e</code>), or piped to <code>node</code> via 307<code>STDIN</code>, are treated as <a href="esm.html">ES modules</a> when the <code>--input-type=module</code> flag 308is set.</p> 309<pre><code class="language-bash">node --input-type=module --<span class="hljs-built_in">eval</span> <span class="hljs-string">"import { sep } from 'path'; console.log(sep);"</span> 310 311<span class="hljs-built_in">echo</span> <span class="hljs-string">"import { sep } from 'path'; console.log(sep);"</span> | node --input-type=module</code></pre> 312<p>For completeness there is also <code>--input-type=commonjs</code>, for explicitly running 313string input as CommonJS. This is the default behavior if <code>--input-type</code> is 314unspecified.</p> 315</section><section><h3>Determining package manager<span><a class="mark" href="#packages_determining_package_manager" id="packages_determining_package_manager">#</a></span></h3> 316<p></p><div class="api_stability api_stability_1"><a href="documentation.html#documentation_stability_index">Stability: 1</a> - Experimental</div><p></p> 317<p>While all Node.js projects are expected to be installable by all package 318managers once published, their development teams are often required to use one 319specific package manager. To make this process easier, Node.js ships with a 320tool called <a href="corepack.html">Corepack</a> that aims to make all package managers transparently 321available in your environment - provided you have Node.js installed.</p> 322<p>By default Corepack won't enforce any specific package manager and will use 323the generic "Last Known Good" versions associated with each Node.js release, 324but you can improve this experience by setting the <a href="#packages_packagemanager"><code>"packageManager"</code></a> field 325in your project's <code>package.json</code>.</p> 326</section><section><h3>Package entry points<span><a class="mark" href="#packages_package_entry_points" id="packages_package_entry_points">#</a></span></h3> 327<p>In a package’s <code>package.json</code> file, two fields can define entry points for a 328package: <a href="#packages_main"><code>"main"</code></a> and <a href="#packages_exports"><code>"exports"</code></a>. The <a href="#packages_main"><code>"main"</code></a> field is supported 329in all versions of Node.js, but its capabilities are limited: it only defines 330the main entry point of the package.</p> 331<p>The <a href="#packages_exports"><code>"exports"</code></a> field provides an alternative to <a href="#packages_main"><code>"main"</code></a> where the 332package main entry point can be defined while also encapsulating the package, 333<strong>preventing any other entry points besides those defined in <a href="#packages_exports"><code>"exports"</code></a></strong>. 334This encapsulation allows module authors to define a public interface for 335their package.</p> 336<p>If both <a href="#packages_exports"><code>"exports"</code></a> and <a href="#packages_main"><code>"main"</code></a> are defined, the <a href="#packages_exports"><code>"exports"</code></a> field 337takes precedence over <a href="#packages_main"><code>"main"</code></a>. <a href="#packages_exports"><code>"exports"</code></a> are not specific to ES 338modules or CommonJS; <a href="#packages_main"><code>"main"</code></a> is overridden by <a href="#packages_exports"><code>"exports"</code></a> if it 339exists. As such <a href="#packages_main"><code>"main"</code></a> cannot be used as a fallback for CommonJS but it 340can be used as a fallback for legacy versions of Node.js that do not support the 341<a href="#packages_exports"><code>"exports"</code></a> field.</p> 342<p><a href="#packages_conditional_exports">Conditional exports</a> can be used within <a href="#packages_exports"><code>"exports"</code></a> to define different 343package entry points per environment, including whether the package is 344referenced via <code>require</code> or via <code>import</code>. For more information about supporting 345both CommonJS and ES Modules in a single package please consult 346<a href="#packages_dual_commonjs_es_module_packages">the dual CommonJS/ES module packages section</a>.</p> 347<p><strong>Warning</strong>: Introducing the <a href="#packages_exports"><code>"exports"</code></a> field prevents consumers of a 348package from using any entry points that are not defined, including the 349<a href="#packages_node_js_package_json_field_definitions"><code>package.json</code></a> (e.g. <code>require('your-package/package.json')</code>. <strong>This will 350likely be a breaking change.</strong></p> 351<p>To make the introduction of <a href="#packages_exports"><code>"exports"</code></a> non-breaking, ensure that every 352previously supported entry point is exported. It is best to explicitly specify 353entry points so that the package’s public API is well-defined. For example, 354a project that previous exported <code>main</code>, <code>lib</code>, 355<code>feature</code>, and the <code>package.json</code> could use the following <code>package.exports</code>:</p> 356<pre><code class="language-json"><span class="hljs-punctuation">{</span> 357 <span class="hljs-attr">"name"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"my-mod"</span><span class="hljs-punctuation">,</span> 358 <span class="hljs-attr">"exports"</span><span class="hljs-punctuation">:</span> <span class="hljs-punctuation">{</span> 359 <span class="hljs-attr">"."</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./lib/index.js"</span><span class="hljs-punctuation">,</span> 360 <span class="hljs-attr">"./lib"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./lib/index.js"</span><span class="hljs-punctuation">,</span> 361 <span class="hljs-attr">"./lib/index"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./lib/index.js"</span><span class="hljs-punctuation">,</span> 362 <span class="hljs-attr">"./lib/index.js"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./lib/index.js"</span><span class="hljs-punctuation">,</span> 363 <span class="hljs-attr">"./feature"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./feature/index.js"</span><span class="hljs-punctuation">,</span> 364 <span class="hljs-attr">"./feature/index.js"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./feature/index.js"</span><span class="hljs-punctuation">,</span> 365 <span class="hljs-attr">"./package.json"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./package.json"</span> 366 <span class="hljs-punctuation">}</span> 367<span class="hljs-punctuation">}</span></code></pre> 368<p>Alternatively a project could choose to export entire folders:</p> 369<pre><code class="language-json"><span class="hljs-punctuation">{</span> 370 <span class="hljs-attr">"name"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"my-mod"</span><span class="hljs-punctuation">,</span> 371 <span class="hljs-attr">"exports"</span><span class="hljs-punctuation">:</span> <span class="hljs-punctuation">{</span> 372 <span class="hljs-attr">"."</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./lib/index.js"</span><span class="hljs-punctuation">,</span> 373 <span class="hljs-attr">"./lib"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./lib/index.js"</span><span class="hljs-punctuation">,</span> 374 <span class="hljs-attr">"./lib/*"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./lib/*.js"</span><span class="hljs-punctuation">,</span> 375 <span class="hljs-attr">"./feature"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./feature/index.js"</span><span class="hljs-punctuation">,</span> 376 <span class="hljs-attr">"./feature/*"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./feature/*.js"</span><span class="hljs-punctuation">,</span> 377 <span class="hljs-attr">"./package.json"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./package.json"</span> 378 <span class="hljs-punctuation">}</span> 379<span class="hljs-punctuation">}</span></code></pre> 380<p>As a last resort, package encapsulation can be disabled entirely by creating an 381export for the root of the package <code>"./*": "./*"</code>. This exposes every file 382in the package at the cost of disabling the encapsulation and potential tooling 383benefits this provides. As the ES Module loader in Node.js enforces the use of 384<a href="esm.html#esm_mandatory_file_extensions">the full specifier path</a>, exporting the root rather than being explicit 385about entry is less expressive than either of the prior examples. Not only 386is encapsulation lost but module consumers are unable to 387<code>import feature from 'my-mod/feature'</code> as they need to provide the full 388path <code>import feature from 'my-mod/feature/index.js</code>.</p> 389<h4>Main entry point export<span><a class="mark" href="#packages_main_entry_point_export" id="packages_main_entry_point_export">#</a></span></h4> 390<p>To set the main entry point for a package, it is advisable to define both 391<a href="#packages_exports"><code>"exports"</code></a> and <a href="#packages_main"><code>"main"</code></a> in the package’s <a href="#packages_node_js_package_json_field_definitions"><code>package.json</code></a> file:</p> 392<pre><code class="language-json"><span class="hljs-punctuation">{</span> 393 <span class="hljs-attr">"main"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./main.js"</span><span class="hljs-punctuation">,</span> 394 <span class="hljs-attr">"exports"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./main.js"</span> 395<span class="hljs-punctuation">}</span></code></pre> 396<p>When the <a href="#packages_exports"><code>"exports"</code></a> field is defined, all subpaths of the package are 397encapsulated and no longer available to importers. For example, 398<code>require('pkg/subpath.js')</code> throws an <a href="errors.html#errors_err_package_path_not_exported"><code>ERR_PACKAGE_PATH_NOT_EXPORTED</code></a> 399error.</p> 400<p>This encapsulation of exports provides more reliable guarantees 401about package interfaces for tools and when handling semver upgrades for a 402package. It is not a strong encapsulation since a direct require of any 403absolute subpath of the package such as 404<code>require('/path/to/node_modules/pkg/subpath.js')</code> will still load <code>subpath.js</code>.</p> 405<h4>Subpath exports<span><a class="mark" href="#packages_subpath_exports" id="packages_subpath_exports">#</a></span></h4> 406<div class="api_metadata"> 407<span>Added in: v12.7.0</span> 408</div> 409<p>When using the <a href="#packages_exports"><code>"exports"</code></a> field, custom subpaths can be defined along 410with the main entry point by treating the main entry point as the 411<code>"."</code> subpath:</p> 412<pre><code class="language-json"><span class="hljs-punctuation">{</span> 413 <span class="hljs-attr">"main"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./main.js"</span><span class="hljs-punctuation">,</span> 414 <span class="hljs-attr">"exports"</span><span class="hljs-punctuation">:</span> <span class="hljs-punctuation">{</span> 415 <span class="hljs-attr">"."</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./main.js"</span><span class="hljs-punctuation">,</span> 416 <span class="hljs-attr">"./submodule"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./src/submodule.js"</span> 417 <span class="hljs-punctuation">}</span> 418<span class="hljs-punctuation">}</span></code></pre> 419<p>Now only the defined subpath in <a href="#packages_exports"><code>"exports"</code></a> can be imported by a consumer:</p> 420<pre><code class="language-js"><span class="hljs-keyword">import</span> submodule <span class="hljs-keyword">from</span> <span class="hljs-string">'es-module-package/submodule'</span>; 421<span class="hljs-comment">// Loads ./node_modules/es-module-package/src/submodule.js</span></code></pre> 422<p>While other subpaths will error:</p> 423<pre><code class="language-js"><span class="hljs-keyword">import</span> submodule <span class="hljs-keyword">from</span> <span class="hljs-string">'es-module-package/private-module.js'</span>; 424<span class="hljs-comment">// Throws ERR_PACKAGE_PATH_NOT_EXPORTED</span></code></pre> 425<h4>Subpath imports<span><a class="mark" href="#packages_subpath_imports" id="packages_subpath_imports">#</a></span></h4> 426<div class="api_metadata"> 427<span>Added in: v14.6.0, v12.19.0</span> 428</div> 429<p>In addition to the <a href="#packages_exports"><code>"exports"</code></a> field, it is possible to define internal 430package import maps that only apply to import specifiers from within the package 431itself.</p> 432<p>Entries in the imports field must always start with <code>#</code> to ensure they are 433disambiguated from package specifiers.</p> 434<p>For example, the imports field can be used to gain the benefits of conditional 435exports for internal modules:</p> 436<pre><code class="language-json"><span class="hljs-comment">// package.json</span> 437<span class="hljs-punctuation">{</span> 438 <span class="hljs-attr">"imports"</span><span class="hljs-punctuation">:</span> <span class="hljs-punctuation">{</span> 439 <span class="hljs-attr">"#dep"</span><span class="hljs-punctuation">:</span> <span class="hljs-punctuation">{</span> 440 <span class="hljs-attr">"node"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"dep-node-native"</span><span class="hljs-punctuation">,</span> 441 <span class="hljs-attr">"default"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./dep-polyfill.js"</span> 442 <span class="hljs-punctuation">}</span> 443 <span class="hljs-punctuation">}</span><span class="hljs-punctuation">,</span> 444 <span class="hljs-attr">"dependencies"</span><span class="hljs-punctuation">:</span> <span class="hljs-punctuation">{</span> 445 <span class="hljs-attr">"dep-node-native"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"^1.0.0"</span> 446 <span class="hljs-punctuation">}</span> 447<span class="hljs-punctuation">}</span></code></pre> 448<p>where <code>import '#dep'</code> does not get the resolution of the external package 449<code>dep-node-native</code> (including its exports in turn), and instead gets the local 450file <code>./dep-polyfill.js</code> relative to the package in other environments.</p> 451<p>Unlike the <code>"exports"</code> field, the <code>"imports"</code> field permits mapping to external 452packages.</p> 453<p>The resolution rules for the imports field are otherwise 454analogous to the exports field.</p> 455<h4>Subpath patterns<span><a class="mark" href="#packages_subpath_patterns" id="packages_subpath_patterns">#</a></span></h4> 456<div class="api_metadata"> 457<span>Added in: v14.13.0, v12.20.0</span> 458</div> 459<p>For packages with a small number of exports or imports, we recommend 460explicitly listing each exports subpath entry. But for packages that have 461large numbers of subpaths, this might cause <code>package.json</code> bloat and 462maintenance issues.</p> 463<p>For these use cases, subpath export patterns can be used instead:</p> 464<pre><code class="language-json"><span class="hljs-comment">// ./node_modules/es-module-package/package.json</span> 465<span class="hljs-punctuation">{</span> 466 <span class="hljs-attr">"exports"</span><span class="hljs-punctuation">:</span> <span class="hljs-punctuation">{</span> 467 <span class="hljs-attr">"./features/*"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./src/features/*.js"</span> 468 <span class="hljs-punctuation">}</span><span class="hljs-punctuation">,</span> 469 <span class="hljs-attr">"imports"</span><span class="hljs-punctuation">:</span> <span class="hljs-punctuation">{</span> 470 <span class="hljs-attr">"#internal/*"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./src/internal/*.js"</span> 471 <span class="hljs-punctuation">}</span> 472<span class="hljs-punctuation">}</span></code></pre> 473<p><strong><code>*</code> maps expose nested subpaths as it is a string replacement syntax 474only.</strong></p> 475<p>All instances of <code>*</code> on the right hand side will then be replaced with this 476value, including if it contains any <code>/</code> separators.</p> 477<pre><code class="language-js"><span class="hljs-keyword">import</span> featureX <span class="hljs-keyword">from</span> <span class="hljs-string">'es-module-package/features/x'</span>; 478<span class="hljs-comment">// Loads ./node_modules/es-module-package/src/features/x.js</span> 479 480<span class="hljs-keyword">import</span> featureY <span class="hljs-keyword">from</span> <span class="hljs-string">'es-module-package/features/y/y'</span>; 481<span class="hljs-comment">// Loads ./node_modules/es-module-package/src/features/y/y.js</span> 482 483<span class="hljs-keyword">import</span> internalZ <span class="hljs-keyword">from</span> <span class="hljs-string">'#internal/z'</span>; 484<span class="hljs-comment">// Loads ./node_modules/es-module-package/src/internal/z.js</span></code></pre> 485<p>This is a direct static replacement without any special handling for file 486extensions. In the previous example, <code>pkg/features/x.json</code> would be resolved to 487<code>./src/features/x.json.js</code> in the mapping.</p> 488<p>The property of exports being statically enumerable is maintained with exports 489patterns since the individual exports for a package can be determined by 490treating the right hand side target pattern as a <code>**</code> glob against the list of 491files within the package. Because <code>node_modules</code> paths are forbidden in exports 492targets, this expansion is dependent on only the files of the package itself.</p> 493<p>To exclude private subfolders from patterns, <code>null</code> targets can be used:</p> 494<pre><code class="language-json"><span class="hljs-comment">// ./node_modules/es-module-package/package.json</span> 495<span class="hljs-punctuation">{</span> 496 <span class="hljs-attr">"exports"</span><span class="hljs-punctuation">:</span> <span class="hljs-punctuation">{</span> 497 <span class="hljs-attr">"./features/*"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./src/features/*.js"</span><span class="hljs-punctuation">,</span> 498 <span class="hljs-attr">"./features/private-internal/*"</span><span class="hljs-punctuation">:</span> <span class="hljs-keyword">null</span> 499 <span class="hljs-punctuation">}</span> 500<span class="hljs-punctuation">}</span></code></pre> 501<pre><code class="language-js"><span class="hljs-keyword">import</span> featureInternal <span class="hljs-keyword">from</span> <span class="hljs-string">'es-module-package/features/private-internal/m'</span>; 502<span class="hljs-comment">// Throws: ERR_PACKAGE_PATH_NOT_EXPORTED</span> 503 504<span class="hljs-keyword">import</span> featureX <span class="hljs-keyword">from</span> <span class="hljs-string">'es-module-package/features/x'</span>; 505<span class="hljs-comment">// Loads ./node_modules/es-module-package/src/features/x.js</span></code></pre> 506<h4>Exports sugar<span><a class="mark" href="#packages_exports_sugar" id="packages_exports_sugar">#</a></span></h4> 507<div class="api_metadata"> 508<span>Added in: v12.11.0</span> 509</div> 510<p>If the <code>"."</code> export is the only export, the <a href="#packages_exports"><code>"exports"</code></a> field provides sugar 511for this case being the direct <a href="#packages_exports"><code>"exports"</code></a> field value.</p> 512<p>If the <code>"."</code> export has a fallback array or string value, then the 513<a href="#packages_exports"><code>"exports"</code></a> field can be set to this value directly.</p> 514<pre><code class="language-json"><span class="hljs-punctuation">{</span> 515 <span class="hljs-attr">"exports"</span><span class="hljs-punctuation">:</span> <span class="hljs-punctuation">{</span> 516 <span class="hljs-attr">"."</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./main.js"</span> 517 <span class="hljs-punctuation">}</span> 518<span class="hljs-punctuation">}</span></code></pre> 519<p>can be written:</p> 520<pre><code class="language-json"><span class="hljs-punctuation">{</span> 521 <span class="hljs-attr">"exports"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./main.js"</span> 522<span class="hljs-punctuation">}</span></code></pre> 523<h4>Conditional exports<span><a class="mark" href="#packages_conditional_exports" id="packages_conditional_exports">#</a></span></h4> 524<div class="api_metadata"> 525<details class="changelog"><summary>History</summary> 526<table> 527<tbody><tr><th>Version</th><th>Changes</th></tr> 528<tr><td>v13.2.0, v12.16.0</td> 529<td><p><span>Added in: v13.2.0, v12.16.0</span></p></td></tr> 530<tr><td>v13.7.0, v12.16.0</td> 531<td><p>Unflag conditional exports.</p></td></tr> 532</tbody></table> 533</details> 534</div> 535<p>Conditional exports provide a way to map to different paths depending on 536certain conditions. They are supported for both CommonJS and ES module imports.</p> 537<p>For example, a package that wants to provide different ES module exports for 538<code>require()</code> and <code>import</code> can be written:</p> 539<pre><code class="language-json"><span class="hljs-comment">// package.json</span> 540<span class="hljs-punctuation">{</span> 541 <span class="hljs-attr">"main"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./main-require.cjs"</span><span class="hljs-punctuation">,</span> 542 <span class="hljs-attr">"exports"</span><span class="hljs-punctuation">:</span> <span class="hljs-punctuation">{</span> 543 <span class="hljs-attr">"import"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./main-module.js"</span><span class="hljs-punctuation">,</span> 544 <span class="hljs-attr">"require"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./main-require.cjs"</span> 545 <span class="hljs-punctuation">}</span><span class="hljs-punctuation">,</span> 546 <span class="hljs-attr">"type"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"module"</span> 547<span class="hljs-punctuation">}</span></code></pre> 548<p>Node.js implements the following conditions:</p> 549<ul> 550<li><code>"import"</code> - matches when the package is loaded via <code>import</code> or 551<code>import()</code>, or via any top-level import or resolve operation by the 552ECMAScript module loader. Applies regardless of the module format of the 553target file. <em>Always mutually exclusive with <code>"require"</code>.</em></li> 554<li><code>"require"</code> - matches when the package is loaded via <code>require()</code>. The 555referenced file should be loadable with <code>require()</code> although the condition 556matches regardless of the module format of the target file. Expected 557formats include CommonJS, JSON, and native addons but not ES modules as 558<code>require()</code> doesn't support them. <em>Always mutually exclusive with 559<code>"import"</code>.</em></li> 560<li><code>"node"</code> - matches for any Node.js environment. Can be a CommonJS or ES 561module file. <em>This condition should always come after <code>"import"</code> or 562<code>"require"</code>.</em></li> 563<li><code>"node-addons"</code> - similar to <code>"node"</code> and matches for any Node.js environment. 564This condition can be used to provide an entry point which uses native C++ 565addons as opposed to an entry point which is more universal and doesn't rely 566on native addons. This condition can be disabled via the 567<a href="cli.html#cli_no_addons"><code>--no-addons</code> flag</a>.</li> 568<li><code>"default"</code> - the generic fallback that always matches. Can be a CommonJS 569or ES module file. <em>This condition should always come last.</em></li> 570</ul> 571<p>Within the <a href="#packages_exports"><code>"exports"</code></a> object, key order is significant. During condition 572matching, earlier entries have higher priority and take precedence over later 573entries. <em>The general rule is that conditions should be from most specific to 574least specific in object order</em>.</p> 575<p>Using the <code>"import"</code> and <code>"require"</code> conditions can lead to some hazards, 576which are further explained in <a href="#packages_dual_commonjs_es_module_packages">the dual CommonJS/ES module packages section</a>.</p> 577<p>Conditional exports can also be extended to exports subpaths, for example:</p> 578<pre><code class="language-json"><span class="hljs-punctuation">{</span> 579 <span class="hljs-attr">"main"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./main.js"</span><span class="hljs-punctuation">,</span> 580 <span class="hljs-attr">"exports"</span><span class="hljs-punctuation">:</span> <span class="hljs-punctuation">{</span> 581 <span class="hljs-attr">"."</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./main.js"</span><span class="hljs-punctuation">,</span> 582 <span class="hljs-attr">"./feature"</span><span class="hljs-punctuation">:</span> <span class="hljs-punctuation">{</span> 583 <span class="hljs-attr">"node"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./feature-node.js"</span><span class="hljs-punctuation">,</span> 584 <span class="hljs-attr">"default"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./feature.js"</span> 585 <span class="hljs-punctuation">}</span> 586 <span class="hljs-punctuation">}</span> 587<span class="hljs-punctuation">}</span></code></pre> 588<p>Defines a package where <code>require('pkg/feature')</code> and <code>import 'pkg/feature'</code> 589could provide different implementations between Node.js and other JS 590environments.</p> 591<p>When using environment branches, always include a <code>"default"</code> condition where 592possible. Providing a <code>"default"</code> condition ensures that any unknown JS 593environments are able to use this universal implementation, which helps avoid 594these JS environments from having to pretend to be existing environments in 595order to support packages with conditional exports. For this reason, using 596<code>"node"</code> and <code>"default"</code> condition branches is usually preferable to using 597<code>"node"</code> and <code>"browser"</code> condition branches.</p> 598<h4>Nested conditions<span><a class="mark" href="#packages_nested_conditions" id="packages_nested_conditions">#</a></span></h4> 599<p>In addition to direct mappings, Node.js also supports nested condition objects.</p> 600<p>For example, to define a package that only has dual mode entry points for 601use in Node.js but not the browser:</p> 602<pre><code class="language-json"><span class="hljs-punctuation">{</span> 603 <span class="hljs-attr">"main"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./main.js"</span><span class="hljs-punctuation">,</span> 604 <span class="hljs-attr">"exports"</span><span class="hljs-punctuation">:</span> <span class="hljs-punctuation">{</span> 605 <span class="hljs-attr">"node"</span><span class="hljs-punctuation">:</span> <span class="hljs-punctuation">{</span> 606 <span class="hljs-attr">"import"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./feature-node.mjs"</span><span class="hljs-punctuation">,</span> 607 <span class="hljs-attr">"require"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./feature-node.cjs"</span> 608 <span class="hljs-punctuation">}</span><span class="hljs-punctuation">,</span> 609 <span class="hljs-attr">"default"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./feature.mjs"</span><span class="hljs-punctuation">,</span> 610 <span class="hljs-punctuation">}</span> 611<span class="hljs-punctuation">}</span></code></pre> 612<p>Conditions continue to be matched in order as with flat conditions. If 613a nested conditional does not have any mapping it will continue checking 614the remaining conditions of the parent condition. In this way nested 615conditions behave analogously to nested JavaScript <code>if</code> statements.</p> 616<h4>Resolving user conditions<span><a class="mark" href="#packages_resolving_user_conditions" id="packages_resolving_user_conditions">#</a></span></h4> 617<div class="api_metadata"> 618<span>Added in: v14.9.0, v12.19.0</span> 619</div> 620<p>When running Node.js, custom user conditions can be added with the 621<code>--conditions</code> flag:</p> 622<pre><code class="language-bash">node --conditions=development main.js</code></pre> 623<p>which would then resolve the <code>"development"</code> condition in package imports and 624exports, while resolving the existing <code>"node"</code>, <code>"node-addons"</code>, <code>"default"</code>, 625<code>"import"</code>, and <code>"require"</code> conditions as appropriate.</p> 626<p>Any number of custom conditions can be set with repeat flags.</p> 627<h4>Conditions Definitions<span><a class="mark" href="#packages_conditions_definitions" id="packages_conditions_definitions">#</a></span></h4> 628<p>The <code>"import"</code>, <code>"require"</code>, <code>"node"</code>, <code>"node-addons"</code> and <code>"default"</code> 629conditions are defined and implemented in Node.js core, 630<a href="#packages_conditional_exports">as specified above</a>.</p> 631<p>The <code>"node-addons"</code> condition can be used to provide an entry point which 632uses native C++ addons. However, this condition can be disabled via the 633<a href="cli.html#cli_no_addons"><code>--no-addons</code> flag</a>. When using <code>"node-addons"</code>, it's recommended to treat 634<code>"default"</code> as an enhancement that provides a more universal entry point, e.g. 635using WebAssembly instead of a native addon.</p> 636<p>Other condition strings are unknown to Node.js and thus ignored by default. 637Runtimes or tools other than Node.js can use them at their discretion.</p> 638<p>These user conditions can be enabled in Node.js via the <a href="#packages_resolving_user_conditions"><code>--conditions</code> 639flag</a>.</p> 640<p>The following condition definitions are currently endorsed by Node.js:</p> 641<ul> 642<li><code>"browser"</code> - any environment which implements a standard subset of global 643browser APIs available from JavaScript in web browsers, including the DOM 644APIs.</li> 645<li><code>"development"</code> - can be used to define a development-only environment 646entry point. <em>Must always be mutually exclusive with <code>"production"</code>.</em></li> 647<li><code>"production"</code> - can be used to define a production environment entry 648point. <em>Must always be mutually exclusive with <code>"development"</code>.</em></li> 649</ul> 650<p>The above user conditions can be enabled in Node.js via the <a href="#packages_resolving_user_conditions"><code>--conditions</code> 651flag</a>.</p> 652<p>Platform specific conditions such as <code>"deno"</code>, <code>"electron"</code>, or <code>"react-native"</code> 653may be used, but while there remain no implementation or integration intent 654from these platforms, the above are not explicitly endorsed by Node.js.</p> 655<p>New conditions definitions may be added to this list by creating a pull request 656to the <a href="https://github.com/nodejs/node/blob/HEAD/doc/api/packages.md#conditions-definitions">Node.js documentation for this section</a>. The requirements for listing 657a new condition definition here are that:</p> 658<ul> 659<li>The definition should be clear and unambiguous for all implementers.</li> 660<li>The use case for why the condition is needed should be clearly justified.</li> 661<li>There should exist sufficient existing implementation usage.</li> 662<li>The condition name should not conflict with another condition definition or 663condition in wide usage.</li> 664<li>The listing of the condition definition should provide a coordination 665benefit to the ecosystem that wouldn't otherwise be possible. For example, 666this would not necessarily be the case for company-specific or 667application-specific conditions.</li> 668</ul> 669<p>The above definitions may be moved to a dedicated conditions registry in due 670course.</p> 671<h4>Self-referencing a package using its name<span><a class="mark" href="#packages_self_referencing_a_package_using_its_name" id="packages_self_referencing_a_package_using_its_name">#</a></span></h4> 672<div class="api_metadata"> 673<details class="changelog"><summary>History</summary> 674<table> 675<tbody><tr><th>Version</th><th>Changes</th></tr> 676<tr><td>v13.1.0, v12.16.0</td> 677<td><p><span>Added in: v13.1.0, v12.16.0</span></p></td></tr> 678<tr><td>v13.6.0, v12.16.0</td> 679<td><p>Unflag self-referencing a package using its name.</p></td></tr> 680</tbody></table> 681</details> 682</div> 683<p>Within a package, the values defined in the package’s 684<code>package.json</code> <a href="#packages_exports"><code>"exports"</code></a> field can be referenced via the package’s name. 685For example, assuming the <code>package.json</code> is:</p> 686<pre><code class="language-json"><span class="hljs-comment">// package.json</span> 687<span class="hljs-punctuation">{</span> 688 <span class="hljs-attr">"name"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"a-package"</span><span class="hljs-punctuation">,</span> 689 <span class="hljs-attr">"exports"</span><span class="hljs-punctuation">:</span> <span class="hljs-punctuation">{</span> 690 <span class="hljs-attr">"."</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./main.mjs"</span><span class="hljs-punctuation">,</span> 691 <span class="hljs-attr">"./foo"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./foo.js"</span> 692 <span class="hljs-punctuation">}</span> 693<span class="hljs-punctuation">}</span></code></pre> 694<p>Then any module <em>in that package</em> can reference an export in the package itself:</p> 695<pre><code class="language-js"><span class="hljs-comment">// ./a-module.mjs</span> 696<span class="hljs-keyword">import</span> { something } <span class="hljs-keyword">from</span> <span class="hljs-string">'a-package'</span>; <span class="hljs-comment">// Imports "something" from ./main.mjs.</span></code></pre> 697<p>Self-referencing is available only if <code>package.json</code> has <a href="#packages_exports"><code>"exports"</code></a>, and 698will allow importing only what that <a href="#packages_exports"><code>"exports"</code></a> (in the <code>package.json</code>) 699allows. So the code below, given the previous package, will generate a runtime 700error:</p> 701<pre><code class="language-js"><span class="hljs-comment">// ./another-module.mjs</span> 702 703<span class="hljs-comment">// Imports "another" from ./m.mjs. Fails because</span> 704<span class="hljs-comment">// the "package.json" "exports" field</span> 705<span class="hljs-comment">// does not provide an export named "./m.mjs".</span> 706<span class="hljs-keyword">import</span> { another } <span class="hljs-keyword">from</span> <span class="hljs-string">'a-package/m.mjs'</span>;</code></pre> 707<p>Self-referencing is also available when using <code>require</code>, both in an ES module, 708and in a CommonJS one. For example, this code will also work:</p> 709<pre><code class="language-js cjs"><span class="hljs-comment">// ./a-module.js</span> 710<span class="hljs-keyword">const</span> { something } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'a-package/foo'</span>); <span class="hljs-comment">// Loads from ./foo.js.</span></code></pre> 711<p>Finally, self-referencing also works with scoped packages. For example, this 712code will also work:</p> 713<pre><code class="language-json"><span class="hljs-comment">// package.json</span> 714<span class="hljs-punctuation">{</span> 715 <span class="hljs-attr">"name"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"@my/package"</span><span class="hljs-punctuation">,</span> 716 <span class="hljs-attr">"exports"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./index.js"</span> 717<span class="hljs-punctuation">}</span></code></pre> 718 719<pre><input class="js-flavor-selector" type="checkbox" checked aria-label="Show modern ES modules syntax"><pre><code class="language-js cjs"><span class="hljs-comment">// ./index.js</span> 720<span class="hljs-variable language_">module</span>.<span class="hljs-property">exports</span> = <span class="hljs-number">42</span>;</code></pre><code class="language-js cjs"><span class="hljs-comment">// ./other.js</span> 721<span class="hljs-variable language_">console</span>.<span class="hljs-title function_">log</span>(<span class="hljs-built_in">require</span>(<span class="hljs-string">'@my/package'</span>));</code></pre> 722<pre><code class="language-console"><span class="hljs-meta">$ </span><span class="language-bash">node other.js</span> 72342</code></pre> 724</section><section><h3>Dual CommonJS/ES module packages<span><a class="mark" href="#packages_dual_commonjs_es_module_packages" id="packages_dual_commonjs_es_module_packages">#</a></span></h3> 725<p>Prior to the introduction of support for ES modules in Node.js, it was a common 726pattern for package authors to include both CommonJS and ES module JavaScript 727sources in their package, with <code>package.json</code> <a href="#packages_main"><code>"main"</code></a> specifying the 728CommonJS entry point and <code>package.json</code> <code>"module"</code> specifying the ES module 729entry point. 730This enabled Node.js to run the CommonJS entry point while build tools such as 731bundlers used the ES module entry point, since Node.js ignored (and still 732ignores) the top-level <code>"module"</code> field.</p> 733<p>Node.js can now run ES module entry points, and a package can contain both 734CommonJS and ES module entry points (either via separate specifiers such as 735<code>'pkg'</code> and <code>'pkg/es-module'</code>, or both at the same specifier via <a href="#packages_conditional_exports">Conditional 736exports</a>). Unlike in the scenario where <code>"module"</code> is only used by bundlers, 737or ES module files are transpiled into CommonJS on the fly before evaluation by 738Node.js, the files referenced by the ES module entry point are evaluated as ES 739modules.</p> 740<h4>Dual package hazard<span><a class="mark" href="#packages_dual_package_hazard" id="packages_dual_package_hazard">#</a></span></h4> 741<p>When an application is using a package that provides both CommonJS and ES module 742sources, there is a risk of certain bugs if both versions of the package get 743loaded. This potential comes from the fact that the <code>pkgInstance</code> created by 744<code>const pkgInstance = require('pkg')</code> is not the same as the <code>pkgInstance</code> 745created by <code>import pkgInstance from 'pkg'</code> (or an alternative main path like 746<code>'pkg/module'</code>). This is the “dual package hazard,” where two versions of the 747same package can be loaded within the same runtime environment. While it is 748unlikely that an application or package would intentionally load both versions 749directly, it is common for an application to load one version while a dependency 750of the application loads the other version. This hazard can happen because 751Node.js supports intermixing CommonJS and ES modules, and can lead to unexpected 752behavior.</p> 753<p>If the package main export is a constructor, an <code>instanceof</code> comparison of 754instances created by the two versions returns <code>false</code>, and if the export is an 755object, properties added to one (like <code>pkgInstance.foo = 3</code>) are not present on 756the other. This differs from how <code>import</code> and <code>require</code> statements work in 757all-CommonJS or all-ES module environments, respectively, and therefore is 758surprising to users. It also differs from the behavior users are familiar with 759when using transpilation via tools like <a href="https://babeljs.io/">Babel</a> or <a href="https://github.com/standard-things/esm#readme"><code>esm</code></a>.</p> 760<h4>Writing dual packages while avoiding or minimizing hazards<span><a class="mark" href="#packages_writing_dual_packages_while_avoiding_or_minimizing_hazards" id="packages_writing_dual_packages_while_avoiding_or_minimizing_hazards">#</a></span></h4> 761<p>First, the hazard described in the previous section occurs when a package 762contains both CommonJS and ES module sources and both sources are provided for 763use in Node.js, either via separate main entry points or exported paths. A 764package might instead be written where any version of Node.js receives only 765CommonJS sources, and any separate ES module sources the package might contain 766are intended only for other environments such as browsers. Such a package 767would be usable by any version of Node.js, since <code>import</code> can refer to CommonJS 768files; but it would not provide any of the advantages of using ES module syntax.</p> 769<p>A package might also switch from CommonJS to ES module syntax in a <a href="https://semver.org/">breaking 770change</a> version bump. This has the disadvantage that the 771newest version of the package would only be usable in ES module-supporting 772versions of Node.js.</p> 773<p>Every pattern has tradeoffs, but there are two broad approaches that satisfy the 774following conditions:</p> 775<ol> 776<li>The package is usable via both <code>require</code> and <code>import</code>.</li> 777<li>The package is usable in both current Node.js and older versions of Node.js 778that lack support for ES modules.</li> 779<li>The package main entry point, e.g. <code>'pkg'</code> can be used by both <code>require</code> to 780resolve to a CommonJS file and by <code>import</code> to resolve to an ES module file. 781(And likewise for exported paths, e.g. <code>'pkg/feature'</code>.)</li> 782<li>The package provides named exports, e.g. <code>import { name } from 'pkg'</code> rather 783than <code>import pkg from 'pkg'; pkg.name</code>.</li> 784<li>The package is potentially usable in other ES module environments such as 785browsers.</li> 786<li>The hazards described in the previous section are avoided or minimized.</li> 787</ol> 788<h5>Approach #1: Use an ES module wrapper<span><a class="mark" href="#packages_approach_1_use_an_es_module_wrapper" id="packages_approach_1_use_an_es_module_wrapper">#</a></span></h5> 789<p>Write the package in CommonJS or transpile ES module sources into CommonJS, and 790create an ES module wrapper file that defines the named exports. Using 791<a href="#packages_conditional_exports">Conditional exports</a>, the ES module wrapper is used for <code>import</code> and the 792CommonJS entry point for <code>require</code>.</p> 793<pre><code class="language-json"><span class="hljs-comment">// ./node_modules/pkg/package.json</span> 794<span class="hljs-punctuation">{</span> 795 <span class="hljs-attr">"type"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"module"</span><span class="hljs-punctuation">,</span> 796 <span class="hljs-attr">"main"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./index.cjs"</span><span class="hljs-punctuation">,</span> 797 <span class="hljs-attr">"exports"</span><span class="hljs-punctuation">:</span> <span class="hljs-punctuation">{</span> 798 <span class="hljs-attr">"import"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./wrapper.mjs"</span><span class="hljs-punctuation">,</span> 799 <span class="hljs-attr">"require"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./index.cjs"</span> 800 <span class="hljs-punctuation">}</span> 801<span class="hljs-punctuation">}</span></code></pre> 802<p>The preceding example uses explicit extensions <code>.mjs</code> and <code>.cjs</code>. 803If your files use the <code>.js</code> extension, <code>"type": "module"</code> will cause such files 804to be treated as ES modules, just as <code>"type": "commonjs"</code> would cause them 805to be treated as CommonJS. 806See <a href="esm.html#esm_enabling">Enabling</a>.</p> 807<pre><code class="language-js cjs"><span class="hljs-comment">// ./node_modules/pkg/index.cjs</span> 808<span class="hljs-built_in">exports</span>.<span class="hljs-property">name</span> = <span class="hljs-string">'value'</span>;</code></pre> 809<pre><code class="language-js"><span class="hljs-comment">// ./node_modules/pkg/wrapper.mjs</span> 810<span class="hljs-keyword">import</span> cjsModule <span class="hljs-keyword">from</span> <span class="hljs-string">'./index.cjs'</span>; 811<span class="hljs-keyword">export</span> <span class="hljs-keyword">const</span> name = cjsModule.<span class="hljs-property">name</span>;</code></pre> 812<p>In this example, the <code>name</code> from <code>import { name } from 'pkg'</code> is the same 813singleton as the <code>name</code> from <code>const { name } = require('pkg')</code>. Therefore <code>===</code> 814returns <code>true</code> when comparing the two <code>name</code>s and the divergent specifier hazard 815is avoided.</p> 816<p>If the module is not simply a list of named exports, but rather contains a 817unique function or object export like <code>module.exports = function () { ... }</code>, 818or if support in the wrapper for the <code>import pkg from 'pkg'</code> pattern is desired, 819then the wrapper would instead be written to export the default optionally 820along with any named exports as well:</p> 821<pre><code class="language-js"><span class="hljs-keyword">import</span> cjsModule <span class="hljs-keyword">from</span> <span class="hljs-string">'./index.cjs'</span>; 822<span class="hljs-keyword">export</span> <span class="hljs-keyword">const</span> name = cjsModule.<span class="hljs-property">name</span>; 823<span class="hljs-keyword">export</span> <span class="hljs-keyword">default</span> cjsModule;</code></pre> 824<p>This approach is appropriate for any of the following use cases:</p> 825<ul> 826<li>The package is currently written in CommonJS and the author would prefer not 827to refactor it into ES module syntax, but wishes to provide named exports for 828ES module consumers.</li> 829<li>The package has other packages that depend on it, and the end user might 830install both this package and those other packages. For example a <code>utilities</code> 831package is used directly in an application, and a <code>utilities-plus</code> package 832adds a few more functions to <code>utilities</code>. Because the wrapper exports 833underlying CommonJS files, it doesn’t matter if <code>utilities-plus</code> is written in 834CommonJS or ES module syntax; it will work either way.</li> 835<li>The package stores internal state, and the package author would prefer not to 836refactor the package to isolate its state management. See the next section.</li> 837</ul> 838<p>A variant of this approach not requiring conditional exports for consumers could 839be to add an export, e.g. <code>"./module"</code>, to point to an all-ES module-syntax 840version of the package. This could be used via <code>import 'pkg/module'</code> by users 841who are certain that the CommonJS version will not be loaded anywhere in the 842application, such as by dependencies; or if the CommonJS version can be loaded 843but doesn’t affect the ES module version (for example, because the package is 844stateless):</p> 845<pre><code class="language-json"><span class="hljs-comment">// ./node_modules/pkg/package.json</span> 846<span class="hljs-punctuation">{</span> 847 <span class="hljs-attr">"type"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"module"</span><span class="hljs-punctuation">,</span> 848 <span class="hljs-attr">"main"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./index.cjs"</span><span class="hljs-punctuation">,</span> 849 <span class="hljs-attr">"exports"</span><span class="hljs-punctuation">:</span> <span class="hljs-punctuation">{</span> 850 <span class="hljs-attr">"."</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./index.cjs"</span><span class="hljs-punctuation">,</span> 851 <span class="hljs-attr">"./module"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./wrapper.mjs"</span> 852 <span class="hljs-punctuation">}</span> 853<span class="hljs-punctuation">}</span></code></pre> 854<h5>Approach #2: Isolate state<span><a class="mark" href="#packages_approach_2_isolate_state" id="packages_approach_2_isolate_state">#</a></span></h5> 855<p>A <a href="#packages_node_js_package_json_field_definitions"><code>package.json</code></a> file can define the separate CommonJS and ES module entry 856points directly:</p> 857<pre><code class="language-json"><span class="hljs-comment">// ./node_modules/pkg/package.json</span> 858<span class="hljs-punctuation">{</span> 859 <span class="hljs-attr">"type"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"module"</span><span class="hljs-punctuation">,</span> 860 <span class="hljs-attr">"main"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./index.cjs"</span><span class="hljs-punctuation">,</span> 861 <span class="hljs-attr">"exports"</span><span class="hljs-punctuation">:</span> <span class="hljs-punctuation">{</span> 862 <span class="hljs-attr">"import"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./index.mjs"</span><span class="hljs-punctuation">,</span> 863 <span class="hljs-attr">"require"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./index.cjs"</span> 864 <span class="hljs-punctuation">}</span> 865<span class="hljs-punctuation">}</span></code></pre> 866<p>This can be done if both the CommonJS and ES module versions of the package are 867equivalent, for example because one is the transpiled output of the other; and 868the package’s management of state is carefully isolated (or the package is 869stateless).</p> 870<p>The reason that state is an issue is because both the CommonJS and ES module 871versions of the package might get used within an application; for example, the 872user’s application code could <code>import</code> the ES module version while a dependency 873<code>require</code>s the CommonJS version. If that were to occur, two copies of the 874package would be loaded in memory and therefore two separate states would be 875present. This would likely cause hard-to-troubleshoot bugs.</p> 876<p>Aside from writing a stateless package (if JavaScript’s <code>Math</code> were a package, 877for example, it would be stateless as all of its methods are static), there are 878some ways to isolate state so that it’s shared between the potentially loaded 879CommonJS and ES module instances of the package:</p> 880<ol> 881<li> 882<p>If possible, contain all state within an instantiated object. JavaScript’s 883<code>Date</code>, for example, needs to be instantiated to contain state; if it were a 884package, it would be used like this:</p> 885<pre><code class="language-js"><span class="hljs-keyword">import</span> <span class="hljs-title class_">Date</span> <span class="hljs-keyword">from</span> <span class="hljs-string">'date'</span>; 886<span class="hljs-keyword">const</span> someDate = <span class="hljs-keyword">new</span> <span class="hljs-title class_">Date</span>(); 887<span class="hljs-comment">// someDate contains state; Date does not</span></code></pre> 888<p>The <code>new</code> keyword isn’t required; a package’s function can return a new 889object, or modify a passed-in object, to keep the state external to the 890package.</p> 891</li> 892<li> 893<p>Isolate the state in one or more CommonJS files that are shared between the 894CommonJS and ES module versions of the package. For example, if the CommonJS 895and ES module entry points are <code>index.cjs</code> and <code>index.mjs</code>, respectively:</p> 896<pre><code class="language-js cjs"><span class="hljs-comment">// ./node_modules/pkg/index.cjs</span> 897<span class="hljs-keyword">const</span> state = <span class="hljs-built_in">require</span>(<span class="hljs-string">'./state.cjs'</span>); 898<span class="hljs-variable language_">module</span>.<span class="hljs-property">exports</span>.<span class="hljs-property">state</span> = state;</code></pre> 899<pre><code class="language-js"><span class="hljs-comment">// ./node_modules/pkg/index.mjs</span> 900<span class="hljs-keyword">import</span> state <span class="hljs-keyword">from</span> <span class="hljs-string">'./state.cjs'</span>; 901<span class="hljs-keyword">export</span> { 902 state 903};</code></pre> 904<p>Even if <code>pkg</code> is used via both <code>require</code> and <code>import</code> in an application (for 905example, via <code>import</code> in application code and via <code>require</code> by a dependency) 906each reference of <code>pkg</code> will contain the same state; and modifying that 907state from either module system will apply to both.</p> 908</li> 909</ol> 910<p>Any plugins that attach to the package’s singleton would need to separately 911attach to both the CommonJS and ES module singletons.</p> 912<p>This approach is appropriate for any of the following use cases:</p> 913<ul> 914<li>The package is currently written in ES module syntax and the package author 915wants that version to be used wherever such syntax is supported.</li> 916<li>The package is stateless or its state can be isolated without too much 917difficulty.</li> 918<li>The package is unlikely to have other public packages that depend on it, or if 919it does, the package is stateless or has state that need not be shared between 920dependencies or with the overall application.</li> 921</ul> 922<p>Even with isolated state, there is still the cost of possible extra code 923execution between the CommonJS and ES module versions of a package.</p> 924<p>As with the previous approach, a variant of this approach not requiring 925conditional exports for consumers could be to add an export, e.g. 926<code>"./module"</code>, to point to an all-ES module-syntax version of the package:</p> 927<pre><code class="language-json"><span class="hljs-comment">// ./node_modules/pkg/package.json</span> 928<span class="hljs-punctuation">{</span> 929 <span class="hljs-attr">"type"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"module"</span><span class="hljs-punctuation">,</span> 930 <span class="hljs-attr">"main"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./index.cjs"</span><span class="hljs-punctuation">,</span> 931 <span class="hljs-attr">"exports"</span><span class="hljs-punctuation">:</span> <span class="hljs-punctuation">{</span> 932 <span class="hljs-attr">"."</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./index.cjs"</span><span class="hljs-punctuation">,</span> 933 <span class="hljs-attr">"./module"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./index.mjs"</span> 934 <span class="hljs-punctuation">}</span> 935<span class="hljs-punctuation">}</span></code></pre> 936</section><section><h3>Node.js <code>package.json</code> field definitions<span><a class="mark" href="#packages_node_js_package_json_field_definitions" id="packages_node_js_package_json_field_definitions">#</a></span></h3> 937<p>This section describes the fields used by the Node.js runtime. Other tools (such 938as <a href="https://docs.npmjs.com/creating-a-package-json-file">npm</a>) use 939additional fields which are ignored by Node.js and not documented here.</p> 940<p>The following fields in <code>package.json</code> files are used in Node.js:</p> 941<ul> 942<li><a href="#packages_name"><code>"name"</code></a> - Relevant when using named imports within a package. Also used 943by package managers as the name of the package.</li> 944<li><a href="#packages_main"><code>"main"</code></a> - The default module when loading the package, if exports is not 945specified, and in versions of Node.js prior to the introduction of exports.</li> 946<li><a href="#packages_packagemanager"><code>"packageManager"</code></a> - The package manager recommended when contributing to 947the package. Leveraged by the <a href="corepack.html">Corepack</a> shims.</li> 948<li><a href="#packages_type"><code>"type"</code></a> - The package type determining whether to load <code>.js</code> files as 949CommonJS or ES modules.</li> 950<li><a href="#packages_exports"><code>"exports"</code></a> - Package exports and conditional exports. When present, 951limits which submodules can be loaded from within the package.</li> 952<li><a href="#packages_imports"><code>"imports"</code></a> - Package imports, for use by modules within the package 953itself.</li> 954</ul> 955<h4><code>"name"</code><span><a class="mark" href="#packages_name" id="packages_name">#</a></span></h4> 956<div class="api_metadata"> 957<details class="changelog"><summary>History</summary> 958<table> 959<tbody><tr><th>Version</th><th>Changes</th></tr> 960<tr><td>v13.1.0, v12.16.0</td> 961<td><p><span>Added in: v13.1.0, v12.16.0</span></p></td></tr> 962<tr><td>v13.6.0, v12.16.0</td> 963<td><p>Remove the <code>--experimental-resolve-self</code> option.</p></td></tr> 964</tbody></table> 965</details> 966</div> 967<ul> 968<li>Type: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> 969</ul> 970<pre><code class="language-json"><span class="hljs-punctuation">{</span> 971 <span class="hljs-attr">"name"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"package-name"</span> 972<span class="hljs-punctuation">}</span></code></pre> 973<p>The <code>"name"</code> field defines your package’s name. Publishing to the 974<em>npm</em> registry requires a name that satisfies 975<a href="https://docs.npmjs.com/files/package.json#name">certain requirements</a>.</p> 976<p>The <code>"name"</code> field can be used in addition to the <a href="#packages_exports"><code>"exports"</code></a> field to 977<a href="#packages_self_referencing_a_package_using_its_name">self-reference</a> a package using its name.</p> 978<h4><code>"main"</code><span><a class="mark" href="#packages_main" id="packages_main">#</a></span></h4> 979<div class="api_metadata"> 980<span>Added in: v0.4.0</span> 981</div> 982<ul> 983<li>Type: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> 984</ul> 985<pre><code class="language-json"><span class="hljs-punctuation">{</span> 986 <span class="hljs-attr">"main"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./main.js"</span> 987<span class="hljs-punctuation">}</span></code></pre> 988<p>The <code>"main"</code> field defines the script that is used when the <a href="modules.html#modules_folders_as_modules">package directory 989is loaded via <code>require()</code></a>. Its value 990is a path.</p> 991<pre><code class="language-js cjs"><span class="hljs-built_in">require</span>(<span class="hljs-string">'./path/to/directory'</span>); <span class="hljs-comment">// This resolves to ./path/to/directory/main.js.</span></code></pre> 992<p>When a package has an <a href="#packages_exports"><code>"exports"</code></a> field, this will take precedence over the 993<code>"main"</code> field when importing the package by name.</p> 994<h4><code>"packageManager"</code><span><a class="mark" href="#packages_packagemanager" id="packages_packagemanager">#</a></span></h4> 995<div class="api_metadata"> 996<span>Added in: v14.19.0</span> 997</div> 998<p></p><div class="api_stability api_stability_1"><a href="documentation.html#documentation_stability_index">Stability: 1</a> - Experimental</div><p></p> 999<ul> 1000<li>Type: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> 1001</ul> 1002<pre><code class="language-json"><span class="hljs-punctuation">{</span> 1003 <span class="hljs-attr">"packageManager"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"<package manager name>@<version>"</span> 1004<span class="hljs-punctuation">}</span></code></pre> 1005<p>The <code>"packageManager"</code> field defines which package manager is expected to be 1006used when working on the current project. It can set to any of the 1007<a href="corepack.html#corepack_supported_package_managers">supported package managers</a>, and will ensure that your teams use the exact 1008same package manager versions without having to install anything else than 1009Node.js.</p> 1010<p>This field is currently experimental and needs to be opted-in; check the 1011<a href="corepack.html">Corepack</a> page for details about the procedure.</p> 1012<h4><code>"type"</code><span><a class="mark" href="#packages_type" id="packages_type">#</a></span></h4> 1013<div class="api_metadata"> 1014<details class="changelog"><summary>History</summary> 1015<table> 1016<tbody><tr><th>Version</th><th>Changes</th></tr> 1017<tr><td>v13.2.0, v12.17.0</td> 1018<td><p>Unflag <code>--experimental-modules</code>.</p></td></tr> 1019<tr><td>v12.0.0</td> 1020<td><p><span>Added in: v12.0.0</span></p></td></tr> 1021</tbody></table> 1022</details> 1023</div> 1024<ul> 1025<li>Type: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> 1026</ul> 1027<p>The <code>"type"</code> field defines the module format that Node.js uses for all 1028<code>.js</code> files that have that <code>package.json</code> file as their nearest parent.</p> 1029<p>Files ending with <code>.js</code> are loaded as ES modules when the nearest parent 1030<code>package.json</code> file contains a top-level field <code>"type"</code> with a value of 1031<code>"module"</code>.</p> 1032<p>The nearest parent <code>package.json</code> is defined as the first <code>package.json</code> found 1033when searching in the current folder, that folder’s parent, and so on up 1034until a node_modules folder or the volume root is reached.</p> 1035<pre><code class="language-json"><span class="hljs-comment">// package.json</span> 1036<span class="hljs-punctuation">{</span> 1037 <span class="hljs-attr">"type"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"module"</span> 1038<span class="hljs-punctuation">}</span></code></pre> 1039<pre><code class="language-bash"><span class="hljs-comment"># In same folder as preceding package.json</span> 1040node my-app.js <span class="hljs-comment"># Runs as ES module</span></code></pre> 1041<p>If the nearest parent <code>package.json</code> lacks a <code>"type"</code> field, or contains 1042<code>"type": "commonjs"</code>, <code>.js</code> files are treated as <a href="modules.html">CommonJS</a>. If the volume 1043root is reached and no <code>package.json</code> is found, <code>.js</code> files are treated as 1044<a href="modules.html">CommonJS</a>.</p> 1045<p><code>import</code> statements of <code>.js</code> files are treated as ES modules if the nearest 1046parent <code>package.json</code> contains <code>"type": "module"</code>.</p> 1047<pre><code class="language-js"><span class="hljs-comment">// my-app.js, part of the same example as above</span> 1048<span class="hljs-keyword">import</span> <span class="hljs-string">'./startup.js'</span>; <span class="hljs-comment">// Loaded as ES module because of package.json</span></code></pre> 1049<p>Regardless of the value of the <code>"type"</code> field, <code>.mjs</code> files are always treated 1050as ES modules and <code>.cjs</code> files are always treated as CommonJS.</p> 1051<h4><code>"exports"</code><span><a class="mark" href="#packages_exports" id="packages_exports">#</a></span></h4> 1052<div class="api_metadata"> 1053<details class="changelog"><summary>History</summary> 1054<table> 1055<tbody><tr><th>Version</th><th>Changes</th></tr> 1056<tr><td>v14.13.0, v12.20.0</td> 1057<td><p>Add support for <code>"exports"</code> patterns.</p></td></tr> 1058<tr><td>v13.7.0, v12.16.0</td> 1059<td><p>Implement logical conditional exports ordering.</p></td></tr> 1060<tr><td>v13.7.0, v12.16.0</td> 1061<td><p>Remove the <code>--experimental-conditional-exports</code> option.</p></td></tr> 1062<tr><td>v13.2.0, v12.16.0</td> 1063<td><p>Implement conditional exports.</p></td></tr> 1064<tr><td>v12.7.0</td> 1065<td><p><span>Added in: v12.7.0</span></p></td></tr> 1066</tbody></table> 1067</details> 1068</div> 1069<ul> 1070<li>Type: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string[]></a></li> 1071</ul> 1072<pre><code class="language-json"><span class="hljs-punctuation">{</span> 1073 <span class="hljs-attr">"exports"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./index.js"</span> 1074<span class="hljs-punctuation">}</span></code></pre> 1075<p>The <code>"exports"</code> field allows defining the <a href="#packages_package_entry_points">entry points</a> of a package when 1076imported by name loaded either via a <code>node_modules</code> lookup or a 1077<a href="#packages_self_referencing_a_package_using_its_name">self-reference</a> to its own name. It is supported in Node.js 12+ as an 1078alternative to the <a href="#packages_main"><code>"main"</code></a> that can support defining <a href="#packages_subpath_exports">subpath exports</a> 1079and <a href="#packages_conditional_exports">conditional exports</a> while encapsulating internal unexported modules.</p> 1080<p><a href="#packages_conditional_exports">Conditional Exports</a> can also be used within <code>"exports"</code> to define different 1081package entry points per environment, including whether the package is 1082referenced via <code>require</code> or via <code>import</code>.</p> 1083<p>All paths defined in the <code>"exports"</code> must be relative file URLs starting with 1084<code>./</code>.</p> 1085<h4><code>"imports"</code><span><a class="mark" href="#packages_imports" id="packages_imports">#</a></span></h4> 1086<div class="api_metadata"> 1087<span>Added in: v14.6.0, v12.19.0</span> 1088</div> 1089<ul> 1090<li>Type: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li> 1091</ul> 1092<pre><code class="language-json"><span class="hljs-comment">// package.json</span> 1093<span class="hljs-punctuation">{</span> 1094 <span class="hljs-attr">"imports"</span><span class="hljs-punctuation">:</span> <span class="hljs-punctuation">{</span> 1095 <span class="hljs-attr">"#dep"</span><span class="hljs-punctuation">:</span> <span class="hljs-punctuation">{</span> 1096 <span class="hljs-attr">"node"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"dep-node-native"</span><span class="hljs-punctuation">,</span> 1097 <span class="hljs-attr">"default"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./dep-polyfill.js"</span> 1098 <span class="hljs-punctuation">}</span> 1099 <span class="hljs-punctuation">}</span><span class="hljs-punctuation">,</span> 1100 <span class="hljs-attr">"dependencies"</span><span class="hljs-punctuation">:</span> <span class="hljs-punctuation">{</span> 1101 <span class="hljs-attr">"dep-node-native"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"^1.0.0"</span> 1102 <span class="hljs-punctuation">}</span> 1103<span class="hljs-punctuation">}</span></code></pre> 1104<p>Entries in the imports field must be strings starting with <code>#</code>.</p> 1105<p>Import maps permit mapping to external packages.</p> 1106<p>This field defines <a href="#packages_subpath_imports">subpath imports</a> for the current package.</p></section> 1107 <!-- API END --> 1108 </div> 1109 </div> 1110 </div> 1111 <script> 1112 'use strict'; 1113 { 1114 const kCustomPreference = 'customDarkTheme'; 1115 const userSettings = sessionStorage.getItem(kCustomPreference); 1116 const themeToggleButton = document.getElementById('theme-toggle-btn'); 1117 if (userSettings === null && window.matchMedia) { 1118 const mq = window.matchMedia('(prefers-color-scheme: dark)'); 1119 if ('onchange' in mq) { 1120 function mqChangeListener(e) { 1121 document.body.classList.toggle('dark-mode', e.matches); 1122 } 1123 mq.addEventListener('change', mqChangeListener); 1124 if (themeToggleButton) { 1125 themeToggleButton.addEventListener('click', function() { 1126 mq.removeEventListener('change', mqChangeListener); 1127 }, { once: true }); 1128 } 1129 } 1130 if (mq.matches) { 1131 document.body.classList.add('dark-mode'); 1132 } 1133 } else if (userSettings === 'true') { 1134 document.body.classList.add('dark-mode'); 1135 } 1136 if (themeToggleButton) { 1137 themeToggleButton.hidden = false; 1138 themeToggleButton.addEventListener('click', function() { 1139 sessionStorage.setItem( 1140 kCustomPreference, 1141 document.body.classList.toggle('dark-mode') 1142 ); 1143 }); 1144 } 1145 } 1146 </script> 1147</body> 1148</html> 1149