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<li><a href="#modules-packages">Modules: Packages</a>
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<li><a href="#main"><code>"main"</code></a></li>
<li><span class="stability_1"><a href="#packagemanager"><code>"packageManager"</code></a></span></li>
<li><a href="#type"><code>"type"</code></a></li>
<li><a href="#exports"><code>"exports"</code></a></li>
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<li><a href="https://nodejs.org/docs/latest-v16.x/api/packages.html">16.x</a></li>
<li><a href="https://nodejs.org/docs/latest-v15.x/api/packages.html">15.x</a></li>
<li><a href="https://nodejs.org/docs/latest-v14.x/api/packages.html">14.x</a></li>
<li><a href="https://nodejs.org/docs/latest-v13.x/api/packages.html">13.x</a></li>
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<details role="navigation" id="toc" open><summary>Table of contents</summary><ul>
<li><a href="#modules-packages">Modules: Packages</a>
<ul>
<li><a href="#introduction">Introduction</a></li>
<li><a href="#determining-module-system">Determining module system</a>
<ul>
<li><a href="#introduction_1">Introduction</a></li>
<li><span class="stability_1"><a href="#syntax-detection">Syntax detection</a></span></li>
<li><a href="#modules-loaders">Modules loaders</a></li>
<li><a href="#packagejson-and-file-extensions"><code>package.json</code> and file extensions</a></li>
<li><a href="#--input-type-flag"><code>--input-type</code> flag</a></li>
</ul>
</li>
<li><span class="stability_1"><a href="#determining-package-manager">Determining package manager</a></span></li>
<li><a href="#package-entry-points">Package entry points</a>
<ul>
<li><a href="#main-entry-point-export">Main entry point export</a></li>
<li><a href="#subpath-exports">Subpath exports</a>
<ul>
<li><a href="#extensions-in-subpaths">Extensions in subpaths</a></li>
</ul>
</li>
<li><a href="#exports-sugar">Exports sugar</a></li>
<li><a href="#subpath-imports">Subpath imports</a></li>
<li><a href="#subpath-patterns">Subpath patterns</a></li>
<li><a href="#conditional-exports">Conditional exports</a></li>
<li><a href="#nested-conditions">Nested conditions</a></li>
<li><a href="#resolving-user-conditions">Resolving user conditions</a></li>
<li><a href="#community-conditions-definitions">Community Conditions Definitions</a></li>
<li><a href="#self-referencing-a-package-using-its-name">Self-referencing a package using its name</a></li>
</ul>
</li>
<li><a href="#dual-commonjses-module-packages">Dual CommonJS/ES module packages</a></li>
<li><a href="#nodejs-packagejson-field-definitions">Node.js <code>package.json</code> field definitions</a>
<ul>
<li><a href="#name"><code>"name"</code></a></li>
<li><a href="#main"><code>"main"</code></a></li>
<li><span class="stability_1"><a href="#packagemanager"><code>"packageManager"</code></a></span></li>
<li><a href="#type"><code>"type"</code></a></li>
<li><a href="#exports"><code>"exports"</code></a></li>
<li><a href="#imports"><code>"imports"</code></a></li>
</ul>
</li>
</ul>
</li>
</ul></details>
<div role="main" id="apicontent">
<h2>Modules: Packages<span><a class="mark" href="#modules-packages" id="modules-packages">#</a></span><a aria-hidden="true" class="legacy" id="packages_modules_packages"></a></h2>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v14.13.0, v12.20.0</td>
<td><p>Add support for <code>"exports"</code> patterns.</p></td></tr>
<tr><td>v14.6.0, v12.19.0</td>
<td><p>Add package <code>"imports"</code> field.</p></td></tr>
<tr><td>v13.7.0, v12.17.0</td>
<td><p>Unflag conditional exports.</p></td></tr>
<tr><td>v13.7.0, v12.16.0</td>
<td><p>Remove the <code>--experimental-conditional-exports</code> option. In 12.16.0, conditional exports are still behind <code>--experimental-modules</code>.</p></td></tr>
<tr><td>v13.6.0, v12.16.0</td>
<td><p>Unflag self-referencing a package using its name.</p></td></tr>
<tr><td>v12.7.0</td>
<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>
<tr><td>v12.0.0</td>
<td><p>Add support for ES modules using <code>.js</code> file extension via <code>package.json</code> <code>"type"</code> field.</p></td></tr>
</tbody></table>
</details>
</div>
<section><h3>Introduction<span><a class="mark" href="#introduction" id="introduction">#</a></span><a aria-hidden="true" class="legacy" id="packages_introduction"></a></h3>
<p>A package is a folder tree described by a <code>package.json</code> file. The package
consists of the folder containing the <code>package.json</code> file and all subfolders
until the next folder containing another <code>package.json</code> file, or a folder
named <code>node_modules</code>.</p>
<p>This page provides guidance for package authors writing <code>package.json</code> files
along with a reference for the <a href="#nodejs-packagejson-field-definitions"><code>package.json</code></a> fields defined by Node.js.</p>
</section><section><h3>Determining module system<span><a class="mark" href="#determining-module-system" id="determining-module-system">#</a></span><a aria-hidden="true" class="legacy" id="packages_determining_module_system"></a></h3>
<h4>Introduction<span><a class="mark" href="#introduction_1" id="introduction_1">#</a></span><a aria-hidden="true" class="legacy" id="packages_introduction_1"></a></h4>
<p>Node.js will treat the following as <a href="esm.html">ES modules</a> when passed to <code>node</code> as the
initial input, or when referenced by <code>import</code> statements or <code>import()</code>
expressions:</p>
<ul>
<li>
<p>Files with an <code>.mjs</code> extension.</p>
</li>
<li>
<p>Files with a <code>.js</code> extension when the nearest parent <code>package.json</code> file
contains a top-level <a href="#type"><code>"type"</code></a> field with a value of <code>"module"</code>.</p>
</li>
<li>
<p>Strings passed in as an argument to <code>--eval</code>, or piped to <code>node</code> via <code>STDIN</code>,
with the flag <code>--input-type=module</code>.</p>
</li>
<li>
<p>Code containing syntax only successfully parsed as <a href="esm.html">ES modules</a>, such as
<code>import</code> or <code>export</code> statements or <code>import.meta</code>, with no explicit marker of
how it should be interpreted. Explicit markers are <code>.mjs</code> or <code>.cjs</code>
extensions, <code>package.json</code> <code>"type"</code> fields with either <code>"module"</code> or
<code>"commonjs"</code> values, or <code>--input-type</code> or <code>--experimental-default-type</code> flags.
Dynamic <code>import()</code> expressions are supported in either CommonJS or ES modules
and would not force a file to be treated as an ES module. See
<a href="#syntax-detection">Syntax detection</a>.</p>
</li>
</ul>
<p>Node.js will treat the following as <a href="modules.html">CommonJS</a> when passed to <code>node</code> as the
initial input, or when referenced by <code>import</code> statements or <code>import()</code>
expressions:</p>
<ul>
<li>
<p>Files with a <code>.cjs</code> extension.</p>
</li>
<li>
<p>Files with a <code>.js</code> extension when the nearest parent <code>package.json</code> file
contains a top-level field <a href="#type"><code>"type"</code></a> 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>
<p>Aside from these explicit cases, there are other cases where Node.js defaults to
one module system or the other based on the value of the
<a href="cli.html#--experimental-default-typetype"><code>--experimental-default-type</code></a> flag:</p>
<ul>
<li>
<p>Files ending in <code>.js</code> or with no extension, if there is no <code>package.json</code> file
present in the same folder or any parent folder.</p>
</li>
<li>
<p>Files ending in <code>.js</code> or with no extension, if the nearest parent
<code>package.json</code> field lacks a <code>"type"</code> field; unless the folder is inside a
<code>node_modules</code> folder. (Package scopes under <code>node_modules</code> are always treated
as CommonJS when the <code>package.json</code> file lacks a <code>"type"</code> field, regardless
of <code>--experimental-default-type</code>, for backward compatibility.)</p>
</li>
<li>
<p>Strings passed in as an argument to <code>--eval</code> or piped to <code>node</code> via <code>STDIN</code>,
when <code>--input-type</code> is unspecified.</p>
</li>
</ul>
<p>This flag currently defaults to <code>"commonjs"</code>, but it may change in the future to
default to <code>"module"</code>. For this reason it is best to be explicit wherever
possible; in particular, package authors should always include the <a href="#type"><code>"type"</code></a>
field in their <code>package.json</code> files, even in packages where all sources are
CommonJS. Being explicit about the <code>type</code> of the package will future-proof the
package in case the default type of Node.js ever changes, and it will also make
things easier for build tools and loaders to determine how the files in the
package should be interpreted.</p>
<h4>Syntax detection<span><a class="mark" href="#syntax-detection" id="syntax-detection">#</a></span><a aria-hidden="true" class="legacy" id="packages_syntax_detection"></a></h4>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v22.7.0</td>
<td><p>Syntax detection is enabled by default.</p></td></tr>
<tr><td>v21.1.0, v20.10.0</td>
<td><p><span>Added in: v21.1.0, v20.10.0</span></p></td></tr>
</tbody></table>
</details>
</div>
<p></p><div class="api_stability api_stability_1"><a href="documentation.html#stability-index">Stability: 1</a>.2 - Release candidate</div><p></p>
<p>Node.js will inspect the source code of ambiguous input to determine whether it
contains ES module syntax; if such syntax is detected, the input will be treated
as an ES module.</p>
<p>Ambiguous input is defined as:</p>
<ul>
<li>Files with a <code>.js</code> extension or no extension; and either no controlling
<code>package.json</code> file or one that lacks a <code>type</code> field; and
<code>--experimental-default-type</code> is not specified.</li>
<li>String input (<code>--eval</code> or STDIN) when neither <code>--input-type</code> nor
<code>--experimental-default-type</code> are specified.</li>
</ul>
<p>ES module syntax is defined as syntax that would throw when evaluated as
CommonJS. This includes the following:</p>
<ul>
<li><code>import</code> statements (but <em>not</em> <code>import()</code> expressions, which are valid in
CommonJS).</li>
<li><code>export</code> statements.</li>
<li><code>import.meta</code> references.</li>
<li><code>await</code> at the top level of a module.</li>
<li>Lexical redeclarations of the CommonJS wrapper variables (<code>require</code>, <code>module</code>,
<code>exports</code>, <code>__dirname</code>, <code>__filename</code>).</li>
</ul>
<h4>Modules loaders<span><a class="mark" href="#modules-loaders" id="modules-loaders">#</a></span><a aria-hidden="true" class="legacy" id="packages_modules_loaders"></a></h4>
<p>Node.js has two systems for resolving a specifier and loading modules.</p>
<p>There is the CommonJS module loader:</p>
<ul>
<li>It is fully synchronous.</li>
<li>It is responsible for handling <code>require()</code> calls.</li>
<li>It is monkey patchable.</li>
<li>It supports <a href="modules.html#folders-as-modules">folders as modules</a>.</li>
<li>When resolving a specifier, if no exact match is found, it will try to add
extensions (<code>.js</code>, <code>.json</code>, and finally <code>.node</code>) and then attempt to resolve
<a href="modules.html#folders-as-modules">folders as modules</a>.</li>
<li>It treats <code>.json</code> as JSON text files.</li>
<li><code>.node</code> files are interpreted as compiled addon modules loaded with
<code>process.dlopen()</code>.</li>
<li>It treats all files that lack <code>.json</code> or <code>.node</code> extensions as JavaScript
text files.</li>
<li>It can only be used to <a href="modules.html#loading-ecmascript-modules-using-require">load ECMASCript modules from CommonJS modules</a> if
the module graph is synchronous (that contains no top-level <code>await</code>).
When used to load a JavaScript text file that is not an ECMAScript module,
the file will be loaded as a CommonJS module.</li>
</ul>
<p>There is the ECMAScript module loader:</p>
<ul>
<li>It is asynchronous, unless it's being used to load modules for <code>require()</code>.</li>
<li>It is responsible for handling <code>import</code> statements and <code>import()</code> expressions.</li>
<li>It is not monkey patchable, can be customized using <a href="esm.html#loaders">loader hooks</a>.</li>
<li>It does not support folders as modules, directory indexes (e.g.
<code>'./startup/index.js'</code>) must be fully specified.</li>
<li>It does no extension searching. A file extension must be provided
when the specifier is a relative or absolute file URL.</li>
<li>It can load JSON modules, but an import type attribute is required.</li>
<li>It accepts only <code>.js</code>, <code>.mjs</code>, and <code>.cjs</code> extensions for JavaScript text
files.</li>
<li>It can be used to load JavaScript CommonJS modules. Such modules
are passed through the <code>cjs-module-lexer</code> to try to identify named exports,
which are available if they can be determined through static analysis.
Imported CommonJS modules have their URLs converted to absolute
paths and are then loaded via the CommonJS module loader.</li>
</ul>
<h4><code>package.json</code> and file extensions<span><a class="mark" href="#packagejson-and-file-extensions" id="packagejson-and-file-extensions">#</a></span><a aria-hidden="true" class="legacy" id="packages_package_json_and_file_extensions"></a></h4>
<p>Within a package, the <a href="#nodejs-packagejson-field-definitions"><code>package.json</code></a> <a href="#type"><code>"type"</code></a> field defines how
Node.js should interpret <code>.js</code> files. If a <code>package.json</code> file does not have a
<code>"type"</code> field, <code>.js</code> files are treated as <a href="modules.html">CommonJS</a>.</p>
<p>A <code>package.json</code> <code>"type"</code> value of <code>"module"</code> tells Node.js to interpret <code>.js</code>
files within that package as using <a href="esm.html">ES module</a> syntax.</p>
<p>The <code>"type"</code> field applies not only to initial entry points (<code>node 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"><span class="hljs-comment">// my-app.js, treated as an ES module because there is a package.json</span>
<span class="hljs-comment">// file in the same folder with "type": "module".</span>
<span class="hljs-keyword">import</span> <span class="hljs-string">'./startup/init.js'</span>;
<span class="hljs-comment">// Loaded as ES module since ./startup contains no package.json file,</span>
<span class="hljs-comment">// and therefore inherits the "type" value from one level up.</span>
<span class="hljs-keyword">import</span> <span class="hljs-string">'commonjs-package'</span>;
<span class="hljs-comment">// Loaded as CommonJS since ./node_modules/commonjs-package/package.json</span>
<span class="hljs-comment">// lacks a "type" field or contains "type": "commonjs".</span>
<span class="hljs-keyword">import</span> <span class="hljs-string">'./node_modules/commonjs-package/index.js'</span>;
<span class="hljs-comment">// Loaded as CommonJS since ./node_modules/commonjs-package/package.json</span>
<span class="hljs-comment">// lacks a "type" field or contains "type": "commonjs".</span></code> <button class="copy-button">copy</button></pre>
<p>Files ending with <code>.mjs</code> are always loaded as <a href="esm.html">ES modules</a> regardless of
the nearest parent <code>package.json</code>.</p>
<p>Files ending with <code>.cjs</code> are always loaded as <a href="modules.html">CommonJS</a> regardless of the
nearest parent <code>package.json</code>.</p>
<pre><code class="language-js"><span class="hljs-keyword">import</span> <span class="hljs-string">'./legacy-file.cjs'</span>;
<span class="hljs-comment">// Loaded as CommonJS since .cjs is always loaded as CommonJS.</span>
<span class="hljs-keyword">import</span> <span class="hljs-string">'commonjs-package/src/index.mjs'</span>;
<span class="hljs-comment">// Loaded as ES module since .mjs is always loaded as ES module.</span></code> <button class="copy-button">copy</button></pre>
<p>The <code>.mjs</code> and <code>.cjs</code> extensions can be used to mix types within the same
package:</p>
<ul>
<li>
<p>Within a <code>"type": "module"</code> package, Node.js can be instructed to
interpret a particular file as <a href="modules.html">CommonJS</a> 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).</p>
</li>
<li>
<p>Within a <code>"type": "commonjs"</code> package, Node.js can be instructed to
interpret a particular file as an <a href="esm.html">ES module</a> 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).</p>
</li>
</ul>
<h4><code>--input-type</code> flag<span><a class="mark" href="#--input-type-flag" id="--input-type-flag">#</a></span><a aria-hidden="true" class="legacy" id="packages_input_type_flag"></a></h4>
<div class="api_metadata">
<span>Added in: v12.0.0</span>
</div>
<p>Strings passed in as an argument to <code>--eval</code> (or <code>-e</code>), or piped to <code>node</code> via
<code>STDIN</code>, are treated as <a href="esm.html">ES modules</a> when the <code>--input-type=module</code> flag
is set.</p>
<pre><code class="language-bash">node --input-type=module --<span class="hljs-built_in">eval</span> <span class="hljs-string">"import { sep } from 'node:path'; console.log(sep);"</span>
<span class="hljs-built_in">echo</span> <span class="hljs-string">"import { sep } from 'node:path'; console.log(sep);"</span> | node --input-type=module</code> <button class="copy-button">copy</button></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>
</section><section><h3>Determining package manager<span><a class="mark" href="#determining-package-manager" id="determining-package-manager">#</a></span><a aria-hidden="true" class="legacy" id="packages_determining_package_manager"></a></h3>
<p></p><div class="api_stability api_stability_1"><a href="documentation.html#stability-index">Stability: 1</a> - Experimental</div><p></p>
<p>While all Node.js projects are expected to be installable by all package
managers once published, their development teams are often required to use one
specific package manager. To make this process easier, Node.js ships with a
tool called <a href="corepack.html">Corepack</a> that aims to make all package managers transparently
available in your environment - provided you have Node.js installed.</p>
<p>By default Corepack won't enforce any specific package manager and will use
the generic "Last Known Good" versions associated with each Node.js release,
but you can improve this experience by setting the <a href="#packagemanager"><code>"packageManager"</code></a> field
in your project's <code>package.json</code>.</p>
</section><section><h3>Package entry points<span><a class="mark" href="#package-entry-points" id="package-entry-points">#</a></span><a aria-hidden="true" class="legacy" id="packages_package_entry_points"></a></h3>
<p>In a package's <code>package.json</code> file, two fields can define entry points for a
package: <a href="#main"><code>"main"</code></a> and <a href="#exports"><code>"exports"</code></a>. Both fields apply to both ES module
and CommonJS module entry points.</p>
<p>The <a href="#main"><code>"main"</code></a> field is supported in all versions of Node.js, but its
capabilities are limited: it only defines the main entry point of the package.</p>
<p>The <a href="#exports"><code>"exports"</code></a> provides a modern alternative to <a href="#main"><code>"main"</code></a> allowing
multiple entry points to be defined, conditional entry resolution support
between environments, and <strong>preventing any other entry points besides those
defined in <a href="#exports"><code>"exports"</code></a></strong>. This encapsulation allows module authors to
clearly define the public interface for their package.</p>
<p>For new packages targeting the currently supported versions of Node.js, the
<a href="#exports"><code>"exports"</code></a> field is recommended. For packages supporting Node.js 10 and
below, the <a href="#main"><code>"main"</code></a> field is required. If both <a href="#exports"><code>"exports"</code></a> and
<a href="#main"><code>"main"</code></a> are defined, the <a href="#exports"><code>"exports"</code></a> field takes precedence over
<a href="#main"><code>"main"</code></a> in supported versions of Node.js.</p>
<p><a href="#conditional-exports">Conditional exports</a> can be used within <a href="#exports"><code>"exports"</code></a> to define different
package entry points per environment, including whether the package is
referenced via <code>require</code> or via <code>import</code>. For more information about supporting
both CommonJS and ES modules in a single package please consult
<a href="#dual-commonjses-module-packages">the dual CommonJS/ES module packages section</a>.</p>
<p>Existing packages introducing the <a href="#exports"><code>"exports"</code></a> field will prevent consumers
of the package from using any entry points that are not defined, including the
<a href="#nodejs-packagejson-field-definitions"><code>package.json</code></a> (e.g. <code>require('your-package/package.json')</code>). <strong>This will
likely be a breaking change.</strong></p>
<p>To make the introduction of <a href="#exports"><code>"exports"</code></a> non-breaking, ensure that every
previously supported entry point is exported. It is best to explicitly specify
entry points so that the package's public API is well-defined. For example,
a project that previously exported <code>main</code>, <code>lib</code>,
<code>feature</code>, and the <code>package.json</code> could use the following <code>package.exports</code>:</p>
<pre><code class="language-json"><span class="hljs-punctuation">{</span>
<span class="hljs-attr">"name"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"my-package"</span><span class="hljs-punctuation">,</span>
<span class="hljs-attr">"exports"</span><span class="hljs-punctuation">:</span> <span class="hljs-punctuation">{</span>
<span class="hljs-attr">"."</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./lib/index.js"</span><span class="hljs-punctuation">,</span>
<span class="hljs-attr">"./lib"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./lib/index.js"</span><span class="hljs-punctuation">,</span>
<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>
<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>
<span class="hljs-attr">"./feature"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./feature/index.js"</span><span class="hljs-punctuation">,</span>
<span class="hljs-attr">"./feature/index"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./feature/index.js"</span><span class="hljs-punctuation">,</span>
<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>
<span class="hljs-attr">"./package.json"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./package.json"</span>
<span class="hljs-punctuation">}</span>
<span class="hljs-punctuation">}</span></code> <button class="copy-button">copy</button></pre>
<p>Alternatively a project could choose to export entire folders both with and
without extensioned subpaths using export patterns:</p>
<pre><code class="language-json"><span class="hljs-punctuation">{</span>
<span class="hljs-attr">"name"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"my-package"</span><span class="hljs-punctuation">,</span>
<span class="hljs-attr">"exports"</span><span class="hljs-punctuation">:</span> <span class="hljs-punctuation">{</span>
<span class="hljs-attr">"."</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./lib/index.js"</span><span class="hljs-punctuation">,</span>
<span class="hljs-attr">"./lib"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./lib/index.js"</span><span class="hljs-punctuation">,</span>
<span class="hljs-attr">"./lib/*"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./lib/*.js"</span><span class="hljs-punctuation">,</span>
<span class="hljs-attr">"./lib/*.js"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./lib/*.js"</span><span class="hljs-punctuation">,</span>
<span class="hljs-attr">"./feature"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./feature/index.js"</span><span class="hljs-punctuation">,</span>
<span class="hljs-attr">"./feature/*"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./feature/*.js"</span><span class="hljs-punctuation">,</span>
<span class="hljs-attr">"./feature/*.js"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./feature/*.js"</span><span class="hljs-punctuation">,</span>
<span class="hljs-attr">"./package.json"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./package.json"</span>
<span class="hljs-punctuation">}</span>
<span class="hljs-punctuation">}</span></code> <button class="copy-button">copy</button></pre>
<p>With the above providing backwards-compatibility for any minor package versions,
a future major change for the package can then properly restrict the exports
to only the specific feature exports exposed:</p>
<pre><code class="language-json"><span class="hljs-punctuation">{</span>
<span class="hljs-attr">"name"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"my-package"</span><span class="hljs-punctuation">,</span>
<span class="hljs-attr">"exports"</span><span class="hljs-punctuation">:</span> <span class="hljs-punctuation">{</span>
<span class="hljs-attr">"."</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./lib/index.js"</span><span class="hljs-punctuation">,</span>
<span class="hljs-attr">"./feature/*.js"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./feature/*.js"</span><span class="hljs-punctuation">,</span>
<span class="hljs-attr">"./feature/internal/*"</span><span class="hljs-punctuation">:</span> <span class="hljs-literal"><span class="hljs-keyword">null</span></span>
<span class="hljs-punctuation">}</span>
<span class="hljs-punctuation">}</span></code> <button class="copy-button">copy</button></pre>
<h4>Main entry point export<span><a class="mark" href="#main-entry-point-export" id="main-entry-point-export">#</a></span><a aria-hidden="true" class="legacy" id="packages_main_entry_point_export"></a></h4>
<p>When writing a new package, it is recommended to use the <a href="#exports"><code>"exports"</code></a> field:</p>
<pre><code class="language-json"><span class="hljs-punctuation">{</span>
<span class="hljs-attr">"exports"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./index.js"</span>
<span class="hljs-punctuation">}</span></code> <button class="copy-button">copy</button></pre>
<p>When the <a href="#exports"><code>"exports"</code></a> field is defined, all subpaths of the package are
encapsulated and no longer available to importers. For example,
<code>require('pkg/subpath.js')</code> throws an <a href="errors.html#err_package_path_not_exported"><code>ERR_PACKAGE_PATH_NOT_EXPORTED</code></a>
error.</p>
<p>This encapsulation of exports provides more reliable guarantees
about package interfaces for tools and when handling semver upgrades for a
package. It is not a strong encapsulation since a direct require of any
absolute subpath of the package such as
<code>require('/path/to/node_modules/pkg/subpath.js')</code> will still load <code>subpath.js</code>.</p>
<p>All currently supported versions of Node.js and modern build tools support the
<code>"exports"</code> field. For projects using an older version of Node.js or a related
build tool, compatibility can be achieved by including the <code>"main"</code> field
alongside <code>"exports"</code> pointing to the same module:</p>
<pre><code class="language-json"><span class="hljs-punctuation">{</span>
<span class="hljs-attr">"main"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./index.js"</span><span class="hljs-punctuation">,</span>
<span class="hljs-attr">"exports"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./index.js"</span>
<span class="hljs-punctuation">}</span></code> <button class="copy-button">copy</button></pre>
<h4>Subpath exports<span><a class="mark" href="#subpath-exports" id="subpath-exports">#</a></span><a aria-hidden="true" class="legacy" id="packages_subpath_exports"></a></h4>
<div class="api_metadata">
<span>Added in: v12.7.0</span>
</div>
<p>When using the <a href="#exports"><code>"exports"</code></a> field, custom subpaths can be defined along
with the main entry point by treating the main entry point as the
<code>"."</code> subpath:</p>
<pre><code class="language-json"><span class="hljs-punctuation">{</span>
<span class="hljs-attr">"exports"</span><span class="hljs-punctuation">:</span> <span class="hljs-punctuation">{</span>
<span class="hljs-attr">"."</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./index.js"</span><span class="hljs-punctuation">,</span>
<span class="hljs-attr">"./submodule.js"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./src/submodule.js"</span>
<span class="hljs-punctuation">}</span>
<span class="hljs-punctuation">}</span></code> <button class="copy-button">copy</button></pre>
<p>Now only the defined subpath in <a href="#exports"><code>"exports"</code></a> can be imported by a consumer:</p>
<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.js'</span>;
<span class="hljs-comment">// Loads ./node_modules/es-module-package/src/submodule.js</span></code> <button class="copy-button">copy</button></pre>
<p>While other subpaths will error:</p>
<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>;
<span class="hljs-comment">// Throws ERR_PACKAGE_PATH_NOT_EXPORTED</span></code> <button class="copy-button">copy</button></pre>
<h5>Extensions in subpaths<span><a class="mark" href="#extensions-in-subpaths" id="extensions-in-subpaths">#</a></span><a aria-hidden="true" class="legacy" id="packages_extensions_in_subpaths"></a></h5>
<p>Package authors should provide either extensioned (<code>import 'pkg/subpath.js'</code>) or
extensionless (<code>import 'pkg/subpath'</code>) subpaths in their exports. This ensures
that there is only one subpath for each exported module so that all dependents
import the same consistent specifier, keeping the package contract clear for
consumers and simplifying package subpath completions.</p>
<p>Traditionally, packages tended to use the extensionless style, which has the
benefits of readability and of masking the true path of the file within the
package.</p>
<p>With <a href="https://github.com/WICG/import-maps">import maps</a> now providing a standard for package resolution in browsers
and other JavaScript runtimes, using the extensionless style can result in
bloated import map definitions. Explicit file extensions can avoid this issue by
enabling the import map to utilize a <a href="https://github.com/WICG/import-maps#packages-via-trailing-slashes">packages folder mapping</a> to map multiple
subpaths where possible instead of a separate map entry per package subpath
export. This also mirrors the requirement of using <a href="esm.html#mandatory-file-extensions">the full specifier path</a>
in relative and absolute import specifiers.</p>
<h4>Exports sugar<span><a class="mark" href="#exports-sugar" id="exports-sugar">#</a></span><a aria-hidden="true" class="legacy" id="packages_exports_sugar"></a></h4>
<div class="api_metadata">
<span>Added in: v12.11.0</span>
</div>
<p>If the <code>"."</code> export is the only export, the <a href="#exports"><code>"exports"</code></a> field provides sugar
for this case being the direct <a href="#exports"><code>"exports"</code></a> field value.</p>
<pre><code class="language-json"><span class="hljs-punctuation">{</span>
<span class="hljs-attr">"exports"</span><span class="hljs-punctuation">:</span> <span class="hljs-punctuation">{</span>
<span class="hljs-attr">"."</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./index.js"</span>
<span class="hljs-punctuation">}</span>
<span class="hljs-punctuation">}</span></code> <button class="copy-button">copy</button></pre>
<p>can be written:</p>
<pre><code class="language-json"><span class="hljs-punctuation">{</span>
<span class="hljs-attr">"exports"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./index.js"</span>
<span class="hljs-punctuation">}</span></code> <button class="copy-button">copy</button></pre>
<h4>Subpath imports<span><a class="mark" href="#subpath-imports" id="subpath-imports">#</a></span><a aria-hidden="true" class="legacy" id="packages_subpath_imports"></a></h4>
<div class="api_metadata">
<span>Added in: v14.6.0, v12.19.0</span>
</div>
<p>In addition to the <a href="#exports"><code>"exports"</code></a> field, there is a package <code>"imports"</code> field
to create private mappings that only apply to import specifiers from within the
package itself.</p>
<p>Entries in the <code>"imports"</code> field must always start with <code>#</code> to ensure they are
disambiguated from external package specifiers.</p>
<p>For example, the imports field can be used to gain the benefits of conditional
exports for internal modules:</p>
<pre><code class="language-json"><span class="hljs-comment">// package.json</span>
<span class="hljs-punctuation">{</span>
<span class="hljs-attr">"imports"</span><span class="hljs-punctuation">:</span> <span class="hljs-punctuation">{</span>
<span class="hljs-attr">"#dep"</span><span class="hljs-punctuation">:</span> <span class="hljs-punctuation">{</span>
<span class="hljs-attr">"node"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"dep-node-native"</span><span class="hljs-punctuation">,</span>
<span class="hljs-attr">"default"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./dep-polyfill.js"</span>
<span class="hljs-punctuation">}</span>
<span class="hljs-punctuation">}</span><span class="hljs-punctuation">,</span>
<span class="hljs-attr">"dependencies"</span><span class="hljs-punctuation">:</span> <span class="hljs-punctuation">{</span>
<span class="hljs-attr">"dep-node-native"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"^1.0.0"</span>
<span class="hljs-punctuation">}</span>
<span class="hljs-punctuation">}</span></code> <button class="copy-button">copy</button></pre>
<p>where <code>import '#dep'</code> does not get the resolution of the external package
<code>dep-node-native</code> (including its exports in turn), and instead gets the local
file <code>./dep-polyfill.js</code> relative to the package in other environments.</p>
<p>Unlike the <code>"exports"</code> field, the <code>"imports"</code> field permits mapping to external
packages.</p>
<p>The resolution rules for the imports field are otherwise analogous to the
exports field.</p>
<h4>Subpath patterns<span><a class="mark" href="#subpath-patterns" id="subpath-patterns">#</a></span><a aria-hidden="true" class="legacy" id="packages_subpath_patterns"></a></h4>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v16.10.0, v14.19.0</td>
<td><p>Support pattern trailers in "imports" field.</p></td></tr>
<tr><td>v16.9.0, v14.19.0</td>
<td><p>Support pattern trailers.</p></td></tr>
<tr><td>v14.13.0, v12.20.0</td>
<td><p><span>Added in: v14.13.0, v12.20.0</span></p></td></tr>
</tbody></table>
</details>
</div>
<p>For packages with a small number of exports or imports, we recommend
explicitly listing each exports subpath entry. But for packages that have
large numbers of subpaths, this might cause <code>package.json</code> bloat and
maintenance issues.</p>
<p>For these use cases, subpath export patterns can be used instead:</p>
<pre><code class="language-json"><span class="hljs-comment">// ./node_modules/es-module-package/package.json</span>
<span class="hljs-punctuation">{</span>
<span class="hljs-attr">"exports"</span><span class="hljs-punctuation">:</span> <span class="hljs-punctuation">{</span>
<span class="hljs-attr">"./features/*.js"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./src/features/*.js"</span>
<span class="hljs-punctuation">}</span><span class="hljs-punctuation">,</span>
<span class="hljs-attr">"imports"</span><span class="hljs-punctuation">:</span> <span class="hljs-punctuation">{</span>
<span class="hljs-attr">"#internal/*.js"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./src/internal/*.js"</span>
<span class="hljs-punctuation">}</span>
<span class="hljs-punctuation">}</span></code> <button class="copy-button">copy</button></pre>
<p><strong><code>*</code> maps expose nested subpaths as it is a string replacement syntax
only.</strong></p>
<p>All instances of <code>*</code> on the right hand side will then be replaced with this
value, including if it contains any <code>/</code> separators.</p>
<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.js'</span>;
<span class="hljs-comment">// Loads ./node_modules/es-module-package/src/features/x.js</span>
<span class="hljs-keyword">import</span> featureY <span class="hljs-keyword">from</span> <span class="hljs-string">'es-module-package/features/y/y.js'</span>;
<span class="hljs-comment">// Loads ./node_modules/es-module-package/src/features/y/y.js</span>
<span class="hljs-keyword">import</span> internalZ <span class="hljs-keyword">from</span> <span class="hljs-string">'#internal/z.js'</span>;
<span class="hljs-comment">// Loads ./node_modules/es-module-package/src/internal/z.js</span></code> <button class="copy-button">copy</button></pre>
<p>This is a direct static matching and replacement without any special handling
for file extensions. Including the <code>"*.js"</code> on both sides of the mapping
restricts the exposed package exports to only JS files.</p>
<p>The property of exports being statically enumerable is maintained with exports
patterns since the individual exports for a package can be determined by
treating the right hand side target pattern as a <code>**</code> glob against the list of
files within the package. Because <code>node_modules</code> paths are forbidden in exports
targets, this expansion is dependent on only the files of the package itself.</p>
<p>To exclude private subfolders from patterns, <code>null</code> targets can be used:</p>
<pre><code class="language-json"><span class="hljs-comment">// ./node_modules/es-module-package/package.json</span>
<span class="hljs-punctuation">{</span>
<span class="hljs-attr">"exports"</span><span class="hljs-punctuation">:</span> <span class="hljs-punctuation">{</span>
<span class="hljs-attr">"./features/*.js"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./src/features/*.js"</span><span class="hljs-punctuation">,</span>
<span class="hljs-attr">"./features/private-internal/*"</span><span class="hljs-punctuation">:</span> <span class="hljs-literal"><span class="hljs-keyword">null</span></span>
<span class="hljs-punctuation">}</span>
<span class="hljs-punctuation">}</span></code> <button class="copy-button">copy</button></pre>
<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.js'</span>;
<span class="hljs-comment">// Throws: ERR_PACKAGE_PATH_NOT_EXPORTED</span>
<span class="hljs-keyword">import</span> featureX <span class="hljs-keyword">from</span> <span class="hljs-string">'es-module-package/features/x.js'</span>;
<span class="hljs-comment">// Loads ./node_modules/es-module-package/src/features/x.js</span></code> <button class="copy-button">copy</button></pre>
<h4>Conditional exports<span><a class="mark" href="#conditional-exports" id="conditional-exports">#</a></span><a aria-hidden="true" class="legacy" id="packages_conditional_exports"></a></h4>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v13.7.0, v12.16.0</td>
<td><p>Unflag conditional exports.</p></td></tr>
<tr><td>v13.2.0, v12.16.0</td>
<td><p><span>Added in: v13.2.0, v12.16.0</span></p></td></tr>
</tbody></table>
</details>
</div>
<p>Conditional exports provide a way to map to different paths depending on
certain conditions. They are supported for both CommonJS and ES module imports.</p>
<p>For example, a package that wants to provide different ES module exports for
<code>require()</code> and <code>import</code> can be written:</p>
<pre><code class="language-json"><span class="hljs-comment">// package.json</span>
<span class="hljs-punctuation">{</span>
<span class="hljs-attr">"exports"</span><span class="hljs-punctuation">:</span> <span class="hljs-punctuation">{</span>
<span class="hljs-attr">"import"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./index-module.js"</span><span class="hljs-punctuation">,</span>
<span class="hljs-attr">"require"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./index-require.cjs"</span>
<span class="hljs-punctuation">}</span><span class="hljs-punctuation">,</span>
<span class="hljs-attr">"type"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"module"</span>
<span class="hljs-punctuation">}</span></code> <button class="copy-button">copy</button></pre>
<p>Node.js implements the following conditions, listed in order from most
specific to least specific as conditions should be defined:</p>
<ul>
<li><code>"node-addons"</code> - similar to <code>"node"</code> and matches for any Node.js environment.
This condition can be used to provide an entry point which uses native C++
addons as opposed to an entry point which is more universal and doesn't rely
on native addons. This condition can be disabled via the
<a href="cli.html#--no-addons"><code>--no-addons</code> flag</a>.</li>
<li><code>"node"</code> - matches for any Node.js environment. Can be a CommonJS or ES
module file. <em>In most cases explicitly calling out the Node.js platform is
not necessary.</em></li>
<li><code>"import"</code> - matches when the package is loaded via <code>import</code> or
<code>import()</code>, or via any top-level import or resolve operation by the
ECMAScript module loader. Applies regardless of the module format of the
target file. <em>Always mutually exclusive with <code>"require"</code>.</em></li>
<li><code>"require"</code> - matches when the package is loaded via <code>require()</code>. The
referenced file should be loadable with <code>require()</code> although the condition
matches regardless of the module format of the target file. Expected
formats include CommonJS, JSON, native addons, and ES modules. <em>Always mutually
exclusive with <code>"import"</code>.</em></li>
<li><code>"module-sync"</code> - matches no matter the package is loaded via <code>import</code>,
<code>import()</code> or <code>require()</code>. The format is expected to be ES modules that does
not contain top-level await in its module graph - if it does,
<code>ERR_REQUIRE_ASYNC_MODULE</code> will be thrown when the module is <code>require()</code>-ed.</li>
<li><code>"default"</code> - the generic fallback that always matches. Can be a CommonJS
or ES module file. <em>This condition should always come last.</em></li>
</ul>
<p>Within the <a href="#exports"><code>"exports"</code></a> object, key order is significant. During condition
matching, earlier entries have higher priority and take precedence over later
entries. <em>The general rule is that conditions should be from most specific to
least specific in object order</em>.</p>
<p>Using the <code>"import"</code> and <code>"require"</code> conditions can lead to some hazards,
which are further explained in <a href="#dual-commonjses-module-packages">the dual CommonJS/ES module packages section</a>.</p>
<p>The <code>"node-addons"</code> condition can be used to provide an entry point which
uses native C++ addons. However, this condition can be disabled via the
<a href="cli.html#--no-addons"><code>--no-addons</code> flag</a>. When using <code>"node-addons"</code>, it's recommended to treat
<code>"default"</code> as an enhancement that provides a more universal entry point, e.g.
using WebAssembly instead of a native addon.</p>
<p>Conditional exports can also be extended to exports subpaths, for example:</p>
<pre><code class="language-json"><span class="hljs-punctuation">{</span>
<span class="hljs-attr">"exports"</span><span class="hljs-punctuation">:</span> <span class="hljs-punctuation">{</span>
<span class="hljs-attr">"."</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./index.js"</span><span class="hljs-punctuation">,</span>
<span class="hljs-attr">"./feature.js"</span><span class="hljs-punctuation">:</span> <span class="hljs-punctuation">{</span>
<span class="hljs-attr">"node"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./feature-node.js"</span><span class="hljs-punctuation">,</span>
<span class="hljs-attr">"default"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./feature.js"</span>
<span class="hljs-punctuation">}</span>
<span class="hljs-punctuation">}</span>
<span class="hljs-punctuation">}</span></code> <button class="copy-button">copy</button></pre>
<p>Defines a package where <code>require('pkg/feature.js')</code> and
<code>import 'pkg/feature.js'</code> could provide different implementations between
Node.js and other JS environments.</p>
<p>When using environment branches, always include a <code>"default"</code> condition where
possible. Providing a <code>"default"</code> condition ensures that any unknown JS
environments are able to use this universal implementation, which helps avoid
these JS environments from having to pretend to be existing environments in
order to support packages with conditional exports. For this reason, using
<code>"node"</code> and <code>"default"</code> condition branches is usually preferable to using
<code>"node"</code> and <code>"browser"</code> condition branches.</p>
<h4>Nested conditions<span><a class="mark" href="#nested-conditions" id="nested-conditions">#</a></span><a aria-hidden="true" class="legacy" id="packages_nested_conditions"></a></h4>
<p>In addition to direct mappings, Node.js also supports nested condition objects.</p>
<p>For example, to define a package that only has dual mode entry points for
use in Node.js but not the browser:</p>
<pre><code class="language-json"><span class="hljs-punctuation">{</span>
<span class="hljs-attr">"exports"</span><span class="hljs-punctuation">:</span> <span class="hljs-punctuation">{</span>
<span class="hljs-attr">"node"</span><span class="hljs-punctuation">:</span> <span class="hljs-punctuation">{</span>
<span class="hljs-attr">"import"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./feature-node.mjs"</span><span class="hljs-punctuation">,</span>
<span class="hljs-attr">"require"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./feature-node.cjs"</span>
<span class="hljs-punctuation">}</span><span class="hljs-punctuation">,</span>
<span class="hljs-attr">"default"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./feature.mjs"</span>
<span class="hljs-punctuation">}</span>
<span class="hljs-punctuation">}</span></code> <button class="copy-button">copy</button></pre>
<p>Conditions continue to be matched in order as with flat conditions. If
a nested condition does not have any mapping it will continue checking
the remaining conditions of the parent condition. In this way nested
conditions behave analogously to nested JavaScript <code>if</code> statements.</p>
<h4>Resolving user conditions<span><a class="mark" href="#resolving-user-conditions" id="resolving-user-conditions">#</a></span><a aria-hidden="true" class="legacy" id="packages_resolving_user_conditions"></a></h4>
<div class="api_metadata">
<span>Added in: v14.9.0, v12.19.0</span>
</div>
<p>When running Node.js, custom user conditions can be added with the
<code>--conditions</code> flag:</p>
<pre><code class="language-bash">node --conditions=development index.js</code> <button class="copy-button">copy</button></pre>
<p>which would then resolve the <code>"development"</code> condition in package imports and
exports, while resolving the existing <code>"node"</code>, <code>"node-addons"</code>, <code>"default"</code>,
<code>"import"</code>, and <code>"require"</code> conditions as appropriate.</p>
<p>Any number of custom conditions can be set with repeat flags.</p>
<p>Typical conditions should only contain alphanumerical characters,
using ":", "-", or "=" as separators if necessary. Anything else may run
into compability issues outside of node.</p>
<p>In node, conditions have very few restrictions, but specifically these include:</p>
<ol>
<li>They must contain at least one character.</li>
<li>They cannot start with "." since they may appear in places that also
allow relative paths.</li>
<li>They cannot contain "," since they may be parsed as a comma-separated
list by some CLI tools.</li>
<li>They cannot be integer property keys like "10" since that can have
unexpected effects on property key ordering for JS objects.</li>
</ol>
<h4>Community Conditions Definitions<span><a class="mark" href="#community-conditions-definitions" id="community-conditions-definitions">#</a></span><a aria-hidden="true" class="legacy" id="packages_community_conditions_definitions"></a></h4>
<p>Condition strings other than the <code>"import"</code>, <code>"require"</code>, <code>"node"</code>, <code>"module-sync"</code>,
<code>"node-addons"</code> and <code>"default"</code> conditions
<a href="#conditional-exports">implemented in Node.js core</a> are ignored by default.</p>
<p>Other platforms may implement other conditions and user conditions can be
enabled in Node.js via the <a href="#resolving-user-conditions"><code>--conditions</code> / <code>-C</code> flag</a>.</p>
<p>Since custom package conditions require clear definitions to ensure correct
usage, a list of common known package conditions and their strict definitions
is provided below to assist with ecosystem coordination.</p>
<ul>
<li><code>"types"</code> - can be used by typing systems to resolve the typing file for
the given export. <em>This condition should always be included first.</em></li>
<li><code>"browser"</code> - any web browser environment.</li>
<li><code>"development"</code> - can be used to define a development-only environment
entry point, for example to provide additional debugging context such as
better error messages when running in a development mode. <em>Must always be
mutually exclusive with <code>"production"</code>.</em></li>
<li><code>"production"</code> - can be used to define a production environment entry
point. <em>Must always be mutually exclusive with <code>"development"</code>.</em></li>
</ul>
<p>For other runtimes, platform-specific condition key definitions are maintained
by the <a href="https://wintercg.org/">WinterCG</a> in the <a href="https://runtime-keys.proposal.wintercg.org/">Runtime Keys</a> proposal specification.</p>
<p>New conditions definitions may be added to this list by creating a pull request
to 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
a new condition definition here are that:</p>
<ul>
<li>The definition should be clear and unambiguous for all implementers.</li>
<li>The use case for why the condition is needed should be clearly justified.</li>
<li>There should exist sufficient existing implementation usage.</li>
<li>The condition name should not conflict with another condition definition or
condition in wide usage.</li>
<li>The listing of the condition definition should provide a coordination
benefit to the ecosystem that wouldn't otherwise be possible. For example,
this would not necessarily be the case for company-specific or
application-specific conditions.</li>
<li>The condition should be such that a Node.js user would expect it to be in
Node.js core documentation. The <code>"types"</code> condition is a good example: It
doesn't really belong in the <a href="https://runtime-keys.proposal.wintercg.org/">Runtime Keys</a> proposal but is a good fit
here in the Node.js docs.</li>
</ul>
<p>The above definitions may be moved to a dedicated conditions registry in due
course.</p>
<h4>Self-referencing a package using its name<span><a class="mark" href="#self-referencing-a-package-using-its-name" id="self-referencing-a-package-using-its-name">#</a></span><a aria-hidden="true" class="legacy" id="packages_self_referencing_a_package_using_its_name"></a></h4>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v13.6.0, v12.16.0</td>
<td><p>Unflag self-referencing a package using its name.</p></td></tr>
<tr><td>v13.1.0, v12.16.0</td>
<td><p><span>Added in: v13.1.0, v12.16.0</span></p></td></tr>
</tbody></table>
</details>
</div>
<p>Within a package, the values defined in the package's
<code>package.json</code> <a href="#exports"><code>"exports"</code></a> field can be referenced via the package's name.
For example, assuming the <code>package.json</code> is:</p>
<pre><code class="language-json"><span class="hljs-comment">// package.json</span>
<span class="hljs-punctuation">{</span>
<span class="hljs-attr">"name"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"a-package"</span><span class="hljs-punctuation">,</span>
<span class="hljs-attr">"exports"</span><span class="hljs-punctuation">:</span> <span class="hljs-punctuation">{</span>
<span class="hljs-attr">"."</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./index.mjs"</span><span class="hljs-punctuation">,</span>
<span class="hljs-attr">"./foo.js"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./foo.js"</span>
<span class="hljs-punctuation">}</span>
<span class="hljs-punctuation">}</span></code> <button class="copy-button">copy</button></pre>
<p>Then any module <em>in that package</em> can reference an export in the package itself:</p>
<pre><code class="language-js"><span class="hljs-comment">// ./a-module.mjs</span>
<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 ./index.mjs.</span></code> <button class="copy-button">copy</button></pre>
<p>Self-referencing is available only if <code>package.json</code> has <a href="#exports"><code>"exports"</code></a>, and
will allow importing only what that <a href="#exports"><code>"exports"</code></a> (in the <code>package.json</code>)
allows. So the code below, given the previous package, will generate a runtime
error:</p>
<pre><code class="language-js"><span class="hljs-comment">// ./another-module.mjs</span>
<span class="hljs-comment">// Imports "another" from ./m.mjs. Fails because</span>
<span class="hljs-comment">// the "package.json" "exports" field</span>
<span class="hljs-comment">// does not provide an export named "./m.mjs".</span>
<span class="hljs-keyword">import</span> { another } <span class="hljs-keyword">from</span> <span class="hljs-string">'a-package/m.mjs'</span>;</code> <button class="copy-button">copy</button></pre>
<p>Self-referencing is also available when using <code>require</code>, both in an ES module,
and in a CommonJS one. For example, this code will also work:</p>
<pre><code class="language-js cjs"><span class="hljs-comment">// ./a-module.js</span>
<span class="hljs-keyword">const</span> { something } = <span class="hljs-built_in">require</span>(<span class="hljs-string">'a-package/foo.js'</span>); <span class="hljs-comment">// Loads from ./foo.js.</span></code> <button class="copy-button">copy</button></pre>
<p>Finally, self-referencing also works with scoped packages. For example, this
code will also work:</p>
<pre><code class="language-json"><span class="hljs-comment">// package.json</span>
<span class="hljs-punctuation">{</span>
<span class="hljs-attr">"name"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"@my/package"</span><span class="hljs-punctuation">,</span>
<span class="hljs-attr">"exports"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./index.js"</span>
<span class="hljs-punctuation">}</span></code> <button class="copy-button">copy</button></pre>
<pre><code class="language-js cjs"><span class="hljs-comment">// ./index.js</span>
<span class="hljs-variable language_">module</span>.<span class="hljs-property">exports</span> = <span class="hljs-number">42</span>;</code> <button class="copy-button">copy</button></pre>
<pre><code class="language-js cjs"><span class="hljs-comment">// ./other.js</span>
<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> <button class="copy-button">copy</button></pre>
<pre><code class="language-console"><span class="hljs-meta prompt_">$ </span><span class="language-bash">node other.js</span>
42</code> <button class="copy-button">copy</button></pre>
</section><section><h3>Dual CommonJS/ES module packages<span><a class="mark" href="#dual-commonjses-module-packages" id="dual-commonjses-module-packages">#</a></span><a aria-hidden="true" class="legacy" id="packages_dual_commonjs_es_module_packages"></a></h3>
<p>See <a href="https://github.com/nodejs/package-examples">the package examples repository</a> for details.</p>
</section><section><h3>Node.js <code>package.json</code> field definitions<span><a class="mark" href="#nodejs-packagejson-field-definitions" id="nodejs-packagejson-field-definitions">#</a></span><a aria-hidden="true" class="legacy" id="packages_node_js_package_json_field_definitions"></a></h3>
<p>This section describes the fields used by the Node.js runtime. Other tools (such
as <a href="https://docs.npmjs.com/cli/v8/configuring-npm/package-json">npm</a>) use
additional fields which are ignored by Node.js and not documented here.</p>
<p>The following fields in <code>package.json</code> files are used in Node.js:</p>
<ul>
<li><a href="#name"><code>"name"</code></a> - Relevant when using named imports within a package. Also used
by package managers as the name of the package.</li>
<li><a href="#main"><code>"main"</code></a> - The default module when loading the package, if exports is not
specified, and in versions of Node.js prior to the introduction of exports.</li>
<li><a href="#packagemanager"><code>"packageManager"</code></a> - The package manager recommended when contributing to
the package. Leveraged by the <a href="corepack.html">Corepack</a> shims.</li>
<li><a href="#type"><code>"type"</code></a> - The package type determining whether to load <code>.js</code> files as
CommonJS or ES modules.</li>
<li><a href="#exports"><code>"exports"</code></a> - Package exports and conditional exports. When present,
limits which submodules can be loaded from within the package.</li>
<li><a href="#imports"><code>"imports"</code></a> - Package imports, for use by modules within the package
itself.</li>
</ul>
<h4><code>"name"</code><span><a class="mark" href="#name" id="name">#</a></span><a aria-hidden="true" class="legacy" id="packages_name"></a></h4>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v13.6.0, v12.16.0</td>
<td><p>Remove the <code>--experimental-resolve-self</code> option.</p></td></tr>
<tr><td>v13.1.0, v12.16.0</td>
<td><p><span>Added in: v13.1.0, v12.16.0</span></p></td></tr>
</tbody></table>
</details>
</div>
<ul>
<li>Type: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li>
</ul>
<pre><code class="language-json"><span class="hljs-punctuation">{</span>
<span class="hljs-attr">"name"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"package-name"</span>
<span class="hljs-punctuation">}</span></code> <button class="copy-button">copy</button></pre>
<p>The <code>"name"</code> field defines your package's name. Publishing to the
<em>npm</em> registry requires a name that satisfies
<a href="https://docs.npmjs.com/files/package.json#name">certain requirements</a>.</p>
<p>The <code>"name"</code> field can be used in addition to the <a href="#exports"><code>"exports"</code></a> field to
<a href="#self-referencing-a-package-using-its-name">self-reference</a> a package using its name.</p>
<h4><code>"main"</code><span><a class="mark" href="#main" id="main">#</a></span><a aria-hidden="true" class="legacy" id="packages_main"></a></h4>
<div class="api_metadata">
<span>Added in: v0.4.0</span>
</div>
<ul>
<li>Type: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li>
</ul>
<pre><code class="language-json"><span class="hljs-punctuation">{</span>
<span class="hljs-attr">"main"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./index.js"</span>
<span class="hljs-punctuation">}</span></code> <button class="copy-button">copy</button></pre>
<p>The <code>"main"</code> field defines the entry point of a package when imported by name
via a <code>node_modules</code> lookup. Its value is a path.</p>
<p>When a package has an <a href="#exports"><code>"exports"</code></a> field, this will take precedence over the
<code>"main"</code> field when importing the package by name.</p>
<p>It also defines the script that is used when the <a href="modules.html#folders-as-modules">package directory is loaded
via <code>require()</code></a>.</p>
<pre><code class="language-js cjs"><span class="hljs-comment">// This resolves to ./path/to/directory/index.js.</span>
<span class="hljs-built_in">require</span>(<span class="hljs-string">'./path/to/directory'</span>);</code> <button class="copy-button">copy</button></pre>
<h4><code>"packageManager"</code><span><a class="mark" href="#packagemanager" id="packagemanager">#</a></span><a aria-hidden="true" class="legacy" id="packages_packagemanager"></a></h4>
<div class="api_metadata">
<span>Added in: v16.9.0, v14.19.0</span>
</div>
<p></p><div class="api_stability api_stability_1"><a href="documentation.html#stability-index">Stability: 1</a> - Experimental</div><p></p>
<ul>
<li>Type: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li>
</ul>
<pre><code class="language-json"><span class="hljs-punctuation">{</span>
<span class="hljs-attr">"packageManager"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"<package manager name>@<version>"</span>
<span class="hljs-punctuation">}</span></code> <button class="copy-button">copy</button></pre>
<p>The <code>"packageManager"</code> field defines which package manager is expected to be
used when working on the current project. It can be set to any of the
<a href="corepack.html#supported-package-managers">supported package managers</a>, and will ensure that your teams use the exact
same package manager versions without having to install anything else other than
Node.js.</p>
<p>This field is currently experimental and needs to be opted-in; check the
<a href="corepack.html">Corepack</a> page for details about the procedure.</p>
<h4><code>"type"</code><span><a class="mark" href="#type" id="type">#</a></span><a aria-hidden="true" class="legacy" id="packages_type"></a></h4>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v13.2.0, v12.17.0</td>
<td><p>Unflag <code>--experimental-modules</code>.</p></td></tr>
<tr><td>v12.0.0</td>
<td><p><span>Added in: v12.0.0</span></p></td></tr>
</tbody></table>
</details>
</div>
<ul>
<li>Type: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li>
</ul>
<p>The <code>"type"</code> field defines the module format that Node.js uses for all
<code>.js</code> files that have that <code>package.json</code> file as their nearest parent.</p>
<p>Files ending with <code>.js</code> are 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 a node_modules folder or the volume root is reached.</p>
<pre><code class="language-json"><span class="hljs-comment">// package.json</span>
<span class="hljs-punctuation">{</span>
<span class="hljs-attr">"type"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"module"</span>
<span class="hljs-punctuation">}</span></code> <button class="copy-button">copy</button></pre>
<pre><code class="language-bash"><span class="hljs-comment"># In same folder as preceding package.json</span>
node my-app.js <span class="hljs-comment"># Runs as ES module</span></code> <button class="copy-button">copy</button></pre>
<p>If the nearest parent <code>package.json</code> lacks a <code>"type"</code> field, or contains
<code>"type": "commonjs"</code>, <code>.js</code> files are treated as <a href="modules.html">CommonJS</a>. If the volume
root is reached and no <code>package.json</code> is found, <code>.js</code> files are treated as
<a href="modules.html">CommonJS</a>.</p>
<p><code>import</code> statements of <code>.js</code> 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"><span class="hljs-comment">// my-app.js, part of the same example as above</span>
<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> <button class="copy-button">copy</button></pre>
<p>Regardless of the value of the <code>"type"</code> field, <code>.mjs</code> files are always treated
as ES modules and <code>.cjs</code> files are always treated as CommonJS.</p>
<h4><code>"exports"</code><span><a class="mark" href="#exports" id="exports">#</a></span><a aria-hidden="true" class="legacy" id="packages_exports"></a></h4>
<div class="api_metadata">
<details class="changelog"><summary>History</summary>
<table>
<tbody><tr><th>Version</th><th>Changes</th></tr>
<tr><td>v14.13.0, v12.20.0</td>
<td><p>Add support for <code>"exports"</code> patterns.</p></td></tr>
<tr><td>v13.7.0, v12.17.0</td>
<td><p>Unflag conditional exports.</p></td></tr>
<tr><td>v13.7.0, v12.16.0</td>
<td><p>Implement logical conditional exports ordering.</p></td></tr>
<tr><td>v13.7.0, v12.16.0</td>
<td><p>Remove the <code>--experimental-conditional-exports</code> option. In 12.16.0, conditional exports are still behind <code>--experimental-modules</code>.</p></td></tr>
<tr><td>v13.2.0, v12.16.0</td>
<td><p>Implement conditional exports.</p></td></tr>
<tr><td>v12.7.0</td>
<td><p><span>Added in: v12.7.0</span></p></td></tr>
</tbody></table>
</details>
</div>
<ul>
<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>
</ul>
<pre><code class="language-json"><span class="hljs-punctuation">{</span>
<span class="hljs-attr">"exports"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./index.js"</span>
<span class="hljs-punctuation">}</span></code> <button class="copy-button">copy</button></pre>
<p>The <code>"exports"</code> field allows defining the <a href="#package-entry-points">entry points</a> of a package when
imported by name loaded either via a <code>node_modules</code> lookup or a
<a href="#self-referencing-a-package-using-its-name">self-reference</a> to its own name. It is supported in Node.js 12+ as an
alternative to the <a href="#main"><code>"main"</code></a> that can support defining <a href="#subpath-exports">subpath exports</a>
and <a href="#conditional-exports">conditional exports</a> while encapsulating internal unexported modules.</p>
<p><a href="#conditional-exports">Conditional Exports</a> can also be used within <code>"exports"</code> to define different
package entry points per environment, including whether the package is
referenced via <code>require</code> or via <code>import</code>.</p>
<p>All paths defined in the <code>"exports"</code> must be relative file URLs starting with
<code>./</code>.</p>
<h4><code>"imports"</code><span><a class="mark" href="#imports" id="imports">#</a></span><a aria-hidden="true" class="legacy" id="packages_imports"></a></h4>
<div class="api_metadata">
<span>Added in: v14.6.0, v12.19.0</span>
</div>
<ul>
<li>Type: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li>
</ul>
<pre><code class="language-json"><span class="hljs-comment">// package.json</span>
<span class="hljs-punctuation">{</span>
<span class="hljs-attr">"imports"</span><span class="hljs-punctuation">:</span> <span class="hljs-punctuation">{</span>
<span class="hljs-attr">"#dep"</span><span class="hljs-punctuation">:</span> <span class="hljs-punctuation">{</span>
<span class="hljs-attr">"node"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"dep-node-native"</span><span class="hljs-punctuation">,</span>
<span class="hljs-attr">"default"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"./dep-polyfill.js"</span>
<span class="hljs-punctuation">}</span>
<span class="hljs-punctuation">}</span><span class="hljs-punctuation">,</span>
<span class="hljs-attr">"dependencies"</span><span class="hljs-punctuation">:</span> <span class="hljs-punctuation">{</span>
<span class="hljs-attr">"dep-node-native"</span><span class="hljs-punctuation">:</span> <span class="hljs-string">"^1.0.0"</span>
<span class="hljs-punctuation">}</span>
<span class="hljs-punctuation">}</span></code> <button class="copy-button">copy</button></pre>
<p>Entries in the imports field must be strings starting with <code>#</code>.</p>
<p>Package imports permit mapping to external packages.</p>
<p>This field defines <a href="#subpath-imports">subpath imports</a> for the current package.</p></section>
<!-- API END -->
</div>
</div>
</div>
</body>
</html>