Configuration

Out of the box, webpack won't require you to use a configuration file. However, it will assume the entry point of your project is src/index.js and will output the result in dist/main.js minified and optimized for production.

Usually, your projects will need to extend this functionality, for this you can create a webpack.config.js file in the root folder and webpack will automatically use it.

All the available configuration options are specified below.

Use a different configuration file

If for some reason you want to use a different configuration file depending on certain situations, you can change this via command line by using the --config flag.

package.json

"scripts": {
  "build": "webpack --config prod.config.js"
}

Set up a new webpack project

Webpack has a huge set of options which might be overwhelming to you, please take advantage of webpack-cli's init command which could rapidly generate webpack configuration files for your project requirements, it will ask you a couple of questions before creating a configuration file.

npx webpack init

npx might prompt you to install @webpack-cli/generators if it is not yet installed in the project or globally. You might also get additional packages installed to your project depending on the choices you've made during the configuration generation.

$ npx webpack init

[webpack-cli] For using this command you need to install: '@webpack-cli/generators' package.
[webpack-cli] Would you like to install '@webpack-cli/generators' package? (That will run 'npm install -D @webpack-cli/generators') (Y/n)
devDependencies:
+ @webpack-cli/generators 2.5.0
? Which of the following JS solutions do you want to use? ES6
? Do you want to use webpack-dev-server? Yes
? Do you want to simplify the creation of HTML files for your bundle? Yes
? Do you want to add PWA support? No
? Which of the following CSS solutions do you want to use? CSS only
? Will you be using PostCSS in your project? Yes
? Do you want to extract CSS for every file? Only for Production
? Do you like to install prettier to format generated configuration? Yes
? Pick a package manager: pnpm
[webpack-cli] ℹ INFO  Initialising project...

devDependencies:
+ @babel/core 7.19.3
+ @babel/preset-env 7.19.4
+ autoprefixer 10.4.12
+ babel-loader 8.2.5
+ css-loader 6.7.1
+ html-webpack-plugin 5.5.0
+ mini-css-extract-plugin 2.6.1
+ postcss 8.4.17
+ postcss-loader 7.0.1
+ prettier 2.7.1
+ style-loader 3.3.1
+ webpack-dev-server 4.11.1
[webpack-cli] Project has been initialised with webpack!

Configuration Languages

Webpack accepts configuration files written in multiple programming and data languages. The list of supported file extensions can be found in the node-interpret package. Using node-interpret, webpack can handle many different types of configuration files.

TypeScript

To write the webpack configuration in TypeScript, you would first install the necessary dependencies, i.e., TypeScript and the relevant type definitions from the DefinitelyTyped project:

npm install --save-dev typescript ts-node @types/node @types/webpack
# and, if using webpack-dev-server < v4.7.0
npm install --save-dev @types/webpack-dev-server

and then proceed to write your configuration:

webpack.config.ts

import path from 'path';
import webpack from 'webpack';
// in case you run into any typescript error when configuring `devServer`
import 'webpack-dev-server';

const config: webpack.Configuration = {
  mode: 'production',
  entry: './foo.js',
  output: {
    path: path.resolve(__dirname, 'dist'),
    filename: 'foo.bundle.js',
  },
};

export default config;

tsconfig.json

{
  "compilerOptions": {
    "allowSyntheticDefaultImports": true,
    "esModuleInterop": true
  }
}

The above sample assumes version >= 2.7 or newer of TypeScript is used with the new esModuleInterop and allowSyntheticDefaultImports compiler options in your tsconfig.json file.

Note that you'll also need to check your tsconfig.json file. If the module in compilerOptions in tsconfig.json is commonjs, the setting is complete, else webpack will fail with an error. This occurs because ts-node does not support any module syntax other than commonjs.

There are three solutions to this issue:

• Modify tsconfig.json.
• Modify tsconfig.json and add settings for ts-node.
• Install tsconfig-paths.

The first option is to open your tsconfig.json file and look for compilerOptions. Set target to "ES5" and module to "CommonJS" (or completely remove the module option).

The second option is to add settings for ts-node:

You can keep "module": "ESNext" for tsc, and if you use webpack, or another build tool, set an override for ts-node. ts-node config

{
  "compilerOptions": {
    "module": "ESNext",
  },
  "ts-node": {
    "compilerOptions": {
      "module": "CommonJS"
    }
  }
}

The third option is to install the tsconfig-paths package:

npm install --save-dev tsconfig-paths

And create a separate TypeScript configuration specifically for your webpack configs:

tsconfig-for-webpack-config.json

{
  "compilerOptions": {
    "module": "commonjs",
    "target": "es5",
    "esModuleInterop": true
  }
}

Then set the environment variable process.env.TS_NODE_PROJECT provided by tsconfig-paths like so:

package.json

{
  "scripts": {
    "build": "cross-env TS_NODE_PROJECT=\"tsconfig-for-webpack-config.json\" webpack"
  }
}

CoffeeScript

Similarly, to use CoffeeScript, you would first install the necessary dependencies:

npm install --save-dev coffeescript

and then proceed to write your configuration:

webpack.config.coffee

HtmlWebpackPlugin = require('html-webpack-plugin')
webpack = require('webpack')
path = require('path')

config =
  mode: 'production'
  entry: './path/to/my/entry/file.js'
  output:
    path: path.resolve(__dirname, 'dist')
    filename: 'my-first-webpack.bundle.js'
  module: rules: [ {
    test: /\.(js|jsx)$/
    use: 'babel-loader'
  } ]
  plugins: [
    new HtmlWebpackPlugin(template: './src/index.html')
  ]

module.exports = config

Babel and JSX

In the example below JSX (React JavaScript Markup) and Babel are used, to create a JSON configuration that webpack can understand.

Courtesy of Jason Miller

First, install the necessary dependencies:

npm install --save-dev babel-register jsxobj babel-preset-es2015

.babelrc

{
  "presets": ["es2015"]
}

webpack.config.babel.js

import jsxobj from 'jsxobj';

// example of an imported plugin
const CustomPlugin = (config) => ({
  ...config,
  name: 'custom-plugin',
});

export default (
  <webpack target="web" watch mode="production">
    <entry path="src/index.js" />
    <resolve>
      <alias
        {...{
          react: 'preact-compat',
          'react-dom': 'preact-compat',
        }}
      />
    </resolve>
    <plugins>
      <CustomPlugin foo="bar" />
    </plugins>
  </webpack>
);

Configuration Types

Besides exporting a single configuration object, there are a few more ways that cover other needs as well.

Exporting a Function

Eventually you will find the need to disambiguate in your webpack.config.js between development and production builds. There are multiple ways to do that. One option is to export a function from your webpack configuration instead of exporting an object. The function will be invoked with two arguments:

• An environment as the first parameter. See the environment options CLI documentation for syntax examples.
• An options map (argv) as the second parameter. This describes the options passed to webpack, with keys such as output-path and mode.

-module.exports = {
+module.exports = function(env, argv) {
+  return {
+    mode: env.production ? 'production' : 'development',
+    devtool: env.production ? 'source-map' : 'eval',
     plugins: [
       new TerserPlugin({
         terserOptions: {
+          compress: argv.mode === 'production' // only if `--mode production` was passed
         }
       })
     ]
+  };
};

Exporting a Promise

Webpack will run the function exported by the configuration file and wait for a Promise to be returned. Handy when you need to asynchronously load configuration variables.

module.exports = () => {
  return new Promise((resolve, reject) => {
    setTimeout(() => {
      resolve({
        entry: './app.js',
        /* ... */
      });
    }, 5000);
  });
};

Exporting multiple configurations

Instead of exporting a single configuration object/function, you may export multiple configurations (multiple functions are supported since webpack 3.1.0). When running webpack, all configurations are built. For instance, this is useful for bundling a library for multiple targets such as AMD and CommonJS:

module.exports = [
  {
    output: {
      filename: './dist-amd.js',
      libraryTarget: 'amd',
    },
    name: 'amd',
    entry: './app.js',
    mode: 'production',
  },
  {
    output: {
      filename: './dist-commonjs.js',
      libraryTarget: 'commonjs',
    },
    name: 'commonjs',
    entry: './app.js',
    mode: 'production',
  },
];

dependencies

In case you have a configuration that depends on the output of another configuration, you can specify a list of dependencies using the dependencies array.

webpack.config.js

module.exports = [
  {
    name: 'client',
    target: 'web',
    // …
  },
  {
    name: 'server',
    target: 'node',
    dependencies: ['client'],
  },
];

parallelism

In case you export multiple configurations, you can use the parallelism option on the configuration array to specify the maximum number of compilers that will compile in parallel.

• Type: number
• Available: 5.22.0+

webpack.config.js

module.exports = [
  {
    //config-1
  },
  {
    //config-2
  },
];
module.exports.parallelism = 1;

Entry and Context

The entry object is where webpack looks to start building the bundle. The context is an absolute string to the directory that contains the entry files.

context

string

The base directory, an absolute path, for resolving entry points and loaders from the configuration.

const path = require('path');

module.exports = {
  //...
  context: path.resolve(__dirname, 'app'),
};

By default, the current working directory of Node.js is used, but it's recommended to pass a value in your configuration. This makes your configuration independent from CWD (current working directory).

entry

string [string] object = { <key> string | [string] | object = { import string | [string], dependOn string | [string], filename string, layer string }} (function() => string | [string] | object = { <key> string | [string] } | object = { import string | [string], dependOn string | [string], filename string })

The point or points where to start the application bundling process. If an array is passed then all items will be processed.

A dynamically loaded module is not an entry point.

A rule to consider: one entry point per HTML page. SPA: one entry point, MPA: multiple entry points.

module.exports = {
  //...
  entry: {
    home: './home.js',
    about: './about.js',
    contact: './contact.js',
  },
};

Naming

If a string or array of strings is passed, the chunk is named main. If an object is passed, each key is the name of a chunk, and the value describes the entry point for the chunk.

Entry descriptor

If an object is passed the value might be a string, array of strings, or a descriptor:

module.exports = {
  //...
  entry: {
    home: './home.js',
    shared: ['react', 'react-dom', 'redux', 'react-redux'],
    catalog: {
      import: './catalog.js',
      filename: 'pages/catalog.js',
      dependOn: 'shared',
      chunkLoading: false, // Disable chunks that are loaded on demand and put everything in the main chunk.
    },
    personal: {
      import: './personal.js',
      filename: 'pages/personal.js',
      dependOn: 'shared',
      chunkLoading: 'jsonp',
      asyncChunks: true, // Create async chunks that are loaded on demand.
      layer: 'name of layer', // set the layer for an entry point
    },
  },
};

Descriptor syntax might be used to pass additional options to an entry point.

Output filename

By default, the output filename for the entry chunk is extracted from output.filename but you can specify a custom output filename for a specific entry:

module.exports = {
  //...
  entry: {
    app: './app.js',
    home: { import: './contact.js', filename: 'pages/[name].js' },
    about: { import: './about.js', filename: 'pages/[name].js' },
  },
};

Descriptor syntax was used here to pass filename-option to the specific entry points.

Dependencies

By default, every entry chunk stores all the modules that it uses. With dependOn option you can share the modules from one entry chunk to another:

module.exports = {
  //...
  entry: {
    app: { import: './app.js', dependOn: 'react-vendors' },
    'react-vendors': ['react', 'react-dom', 'prop-types'],
  },
};

The app chunk will not contain the modules that react-vendors have.

dependOn option can also accept an array of strings:

module.exports = {
  //...
  entry: {
    moment: { import: 'moment-mini', runtime: 'runtime' },
    reactvendors: { import: ['react', 'react-dom'], runtime: 'runtime' },
    testapp: {
      import: './wwwroot/component/TestApp.tsx',
      dependOn: ['reactvendors', 'moment'],
    },
  },
};

Also, you can specify multiple files per entry using an array:

module.exports = {
  //...
  entry: {
    app: { import: ['./app.js', './app2.js'], dependOn: 'react-vendors' },
    'react-vendors': ['react', 'react-dom', 'prop-types'],
  },
};

Dynamic entry

If a function is passed then it will be invoked on every make event.

Note that the make event triggers when webpack starts and for every invalidation when watching for file changes.

module.exports = {
  //...
  entry: () => './demo',
};

or

module.exports = {
  //...
  entry: () => new Promise((resolve) => resolve(['./demo', './demo2'])),
};

For example: you can use dynamic entries to get the actual entries from an external source (remote server, file system content or database):

webpack.config.js

module.exports = {
  entry() {
    return fetchPathsFromSomeExternalSource(); // returns a promise that will be resolved with something like ['src/main-layout.js', 'src/admin-layout.js']
  },
};

When combining with the output.library option: If an array is passed only the last item is exported.

Mode

Providing the mode configuration option tells webpack to use its built-in optimizations accordingly.

string = 'production': 'none' | 'development' | 'production'

Usage

Provide the mode option in the config:

module.exports = {
  mode: 'development',
};

or pass it as a CLI argument:

webpack --mode=development

The following string values are supported:

If not set, webpack sets production as the default value for mode.

Mode: development

// webpack.development.config.js
module.exports = {
  mode: 'development',
};

Mode: production

// webpack.production.config.js
module.exports = {
  mode: 'production',
};

Mode: none

// webpack.custom.config.js
module.exports = {
  mode: 'none',
};

If you want to change the behavior according to the mode variable inside the webpack.config.js, you have to export a function instead of an object:

var config = {
  entry: './app.js',
  //...
};

module.exports = (env, argv) => {
  if (argv.mode === 'development') {
    config.devtool = 'source-map';
  }

  if (argv.mode === 'production') {
    //...
  }

  return config;
};

Output

The top-level output key contains a set of options instructing webpack on how and where it should output your bundles, assets, and anything else you bundle or load with webpack.

output.assetModuleFilename

string = '[hash][ext][query]'

The same as output.filename but for Asset Modules.

[name], [file], [query], [fragment], [base], and [path] are set to an empty string for the assets built from data URI replacements.

output.asyncChunks

boolean = true

Create async chunks that are loaded on demand.

webpack.config.js

module.exports = {
  //...
  output: {
    //...
    asyncChunks: true,
  },
};

output.auxiliaryComment

string object

When used in tandem with output.library and output.libraryTarget, this option allows users to insert comments within the export wrapper. To insert the same comment for each libraryTarget type, set auxiliaryComment to a string:

webpack.config.js

module.exports = {
  //...
  output: {
    library: 'someLibName',
    libraryTarget: 'umd',
    filename: 'someLibName.js',
    auxiliaryComment: 'Test Comment',
  },
};

which will yield the following:

someLibName.js

(function webpackUniversalModuleDefinition(root, factory) {
  // Test Comment
  if (typeof exports === 'object' && typeof module === 'object')
    module.exports = factory(require('lodash'));
  // Test Comment
  else if (typeof define === 'function' && define.amd)
    define(['lodash'], factory);
  // Test Comment
  else if (typeof exports === 'object')
    exports['someLibName'] = factory(require('lodash'));
  // Test Comment
  else root['someLibName'] = factory(root['_']);
})(this, function (__WEBPACK_EXTERNAL_MODULE_1__) {
  // ...
});

For fine-grained control over each libraryTarget comment, pass an object:

webpack.config.js

module.exports = {
  //...
  output: {
    //...
    auxiliaryComment: {
      root: 'Root Comment',
      commonjs: 'CommonJS Comment',
      commonjs2: 'CommonJS2 Comment',
      amd: 'AMD Comment',
    },
  },
};

output.charset

boolean = true

Tells webpack to add charset="utf-8" to the HTML <script> tag.

output.chunkFilename

string = '[id].js' function (pathData, assetInfo) => string

This option determines the name of non-initial chunk files. See output.filename option for details on the possible values.

Note that these filenames need to be generated at runtime to send the requests for chunks. Because of this, placeholders like [name] and [chunkhash] need to add a mapping from chunk id to placeholder value to the output bundle with the webpack runtime. This increases the size and may invalidate the bundle when placeholder value for any chunk changes.

By default [id].js is used or a value inferred from output.filename ([name] is replaced with [id] or [id]. is prepended).

webpack.config.js

module.exports = {
  //...
  output: {
    //...
    chunkFilename: '[id].js',
  },
};

Usage as a function:

webpack.config.js

module.exports = {
  //...
  output: {
    chunkFilename: (pathData) => {
      return pathData.chunk.name === 'main' ? '[name].js' : '[name]/[name].js';
    },
  },
};

output.chunkFormat

false string: 'array-push' | 'commonjs' | 'module' | <any string>

The format of chunks (formats included by default are 'array-push' (web/WebWorker), 'commonjs' (node.js), 'module' (ESM), but others might be added by plugins).

webpack.config.js

module.exports = {
  //...
  output: {
    //...
    chunkFormat: 'commonjs',
  },
};

output.chunkLoadTimeout

number = 120000

The Number of milliseconds before chunk request expires. This option is supported since webpack 2.6.0.

webpack.config.js

module.exports = {
  //...
  output: {
    //...
    chunkLoadTimeout: 30000,
  },
};

output.chunkLoadingGlobal

string = 'webpackChunkwebpack'

The global variable is used by webpack for loading chunks.

webpack.config.js

module.exports = {
  //...
  output: {
    //...
    chunkLoadingGlobal: 'myCustomFunc',
  },
};

output.chunkLoading

false string: 'jsonp' | 'import-scripts' | 'require' | 'async-node' | 'import' | <any string>

The method to load chunks (methods included by default are 'jsonp' (web), 'import' (ESM), 'importScripts' (WebWorker), 'require' (sync node.js), 'async-node' (async node.js), but others might be added by plugins).

webpack.config.js

module.exports = {
  //...
  output: {
    //...
    chunkLoading: 'async-node',
  },
};

output.clean

boolean { dry?: boolean, keep?: RegExp | string | ((filename: string) => boolean) }

module.exports = {
  //...
  output: {
    clean: true, // Clean the output directory before emit.
  },
};

module.exports = {
  //...
  output: {
    clean: {
      dry: true, // Log the assets that should be removed instead of deleting them.
    },
  },
};

module.exports = {
  //...
  output: {
    clean: {
      keep: /ignored\/dir\//, // Keep these assets under 'ignored/dir'.
    },
  },
};

// or

module.exports = {
  //...
  output: {
    clean: {
      keep(asset) {
        return asset.includes('ignored/dir');
      },
    },
  },
};

You can also use it with hook:

webpack.CleanPlugin.getCompilationHooks(compilation).keep.tap(
  'Test',
  (asset) => {
    if (/ignored\/dir\//.test(asset)) return true;
  }
);

output.compareBeforeEmit

boolean = true

Tells webpack to check if to be emitted file already exists and has the same content before writing to the output file system.

module.exports = {
  //...
  output: {
    compareBeforeEmit: false,
  },
};

output.crossOriginLoading

boolean = false string: 'anonymous' | 'use-credentials'

Tells webpack to enable cross-origin loading of chunks. Only takes effect when the target is set to 'web', which uses JSONP for loading on-demand chunks, by adding script tags.

• 'anonymous' - Enable cross-origin loading without credentials
• 'use-credentials' - Enable cross-origin loading with credentials

output.devtoolFallbackModuleFilenameTemplate

string function (info)

A fallback is used when the template string or function above yields duplicates.

See output.devtoolModuleFilenameTemplate.

output.devtoolModuleFilenameTemplate

string = 'webpack://[namespace]/[resource-path]?[loaders]' function (info) => string

This option is only used when devtool uses an option that requires module names.

Customize the names used in each source map's sources array. This can be done by passing a template string or function. For example, when using devtool: 'eval'.

webpack.config.js

module.exports = {
  //...
  output: {
    devtoolModuleFilenameTemplate:
      'webpack://[namespace]/[resource-path]?[loaders]',
  },
};

The following substitutions are available in template strings (via webpack's internal ModuleFilenameHelpers):

When using a function, the same options are available camel-cased via the info parameter:

module.exports = {
  //...
  output: {
    devtoolModuleFilenameTemplate: (info) => {
      return `webpack:///${info.resourcePath}?${info.loaders}`;
    },
  },
};

If multiple modules would result in the same name, output.devtoolFallbackModuleFilenameTemplate is used instead for these modules.

output.devtoolNamespace

string

This option determines the module's namespace used with the output.devtoolModuleFilenameTemplate. When not specified, it will default to the value of: output.uniqueName. It's used to prevent source file path collisions in sourcemaps when loading multiple libraries built with webpack.

For example, if you have 2 libraries, with namespaces library1 and library2, which both have a file ./src/index.js (with potentially different contents), they will expose these files as webpack://library1/./src/index.js and webpack://library2/./src/index.js.

output.enabledChunkLoadingTypes

[string: 'jsonp' | 'import-scripts' | 'require' | 'async-node' | <any string>]

List of chunk loading types enabled for use by entry points. Will be automatically filled by webpack. Only needed when using a function as entry option and returning chunkLoading option from there.

webpack.config.js

module.exports = {
  //...
  output: {
    //...
    enabledChunkLoadingTypes: ['jsonp', 'require'],
  },
};

output.enabledLibraryTypes

[string]

List of library types enabled for use by entry points.

module.exports = {
  //...
  output: {
    enabledLibraryTypes: ['module'],
  },
};

output.enabledWasmLoadingTypes

[string]

List of wasm loading types enabled for use by entry points.

module.exports = {
  //...
  output: {
    enabledWasmLoadingTypes: ['fetch'],
  },
};

output.environment

Tell webpack what kind of ES-features may be used in the generated runtime-code.

module.exports = {
  output: {
    environment: {
      // The environment supports arrow functions ('() => { ... }').
      arrowFunction: true,
      // The environment supports BigInt as literal (123n).
      bigIntLiteral: false,
      // The environment supports const and let for variable declarations.
      const: true,
      // The environment supports destructuring ('{ a, b } = obj').
      destructuring: true,
      // The environment supports an async import() function to import EcmaScript modules.
      dynamicImport: false,
      // The environment supports an async import() when creating a worker, only for web targets at the moment.
      dynamicImportInWorker: false,
      // The environment supports 'for of' iteration ('for (const x of array) { ... }').
      forOf: true,
      // The environment supports 'globalThis'.
      globalThis: true,
      // The environment supports ECMAScript Module syntax to import ECMAScript modules (import ... from '...').
      module: false,
      // The environment supports optional chaining ('obj?.a' or 'obj?.()').
      optionalChaining: true,
      // The environment supports template literals.
      templateLiteral: true,
    },
  },
};

output.filename

string function (pathData, assetInfo) => string

This option determines the name of each output bundle. The bundle is written to the directory specified by the output.path option.

For a single entry point, this can be a static name.

webpack.config.js

module.exports = {
  //...
  output: {
    filename: 'bundle.js',
  },
};

However, when creating multiple bundles via more than one entry point, code splitting, or various plugins, you should use one of the following substitutions to give each bundle a unique name...

Using entry name:

webpack.config.js

module.exports = {
  //...
  output: {
    filename: '[name].bundle.js',
  },
};

Using internal chunk id:

webpack.config.js

module.exports = {
  //...
  output: {
    filename: '[id].bundle.js',
  },
};

Using hashes generated from the generated content:

webpack.config.js

module.exports = {
  //...
  output: {
    filename: '[contenthash].bundle.js',
  },
};

Combining multiple substitutions:

webpack.config.js

module.exports = {
  //...
  output: {
    filename: '[name].[contenthash].bundle.js',
  },
};

Using the function to return the filename:

webpack.config.js

module.exports = {
  //...
  output: {
    filename: (pathData) => {
      return pathData.chunk.name === 'main' ? '[name].js' : '[name]/[name].js';
    },
  },
};

Make sure to read the Caching guide for details. There are more steps involved than only setting this option.

Note this option is called filename but you are still allowed to use something like 'js/[name]/bundle.js' to create a folder structure.

Note this option does not affect output files for on-demand-loaded chunks. It only affects output files that are initially loaded. For on-demand-loaded chunk files, the output.chunkFilename option is used. Files created by loaders also aren't affected. In this case, you would have to try the specific loader's available options.

Template strings

The following substitutions are available in template strings (via webpack's internal TemplatedPathPlugin):

Substitutions available on Compilation-level:

Substitutions available on Chunk-level:

Substitutions available on Module-level:

Substitutions available on File-level:

Substitutions available on URL-level:

The length of hashes ([hash], [contenthash] or [chunkhash]) can be specified using [hash:16] (defaults to 20). Alternatively, specify output.hashDigestLength to configure the length globally.

It is possible to filter out placeholder replacement when you want to use one of the placeholders in the actual file name. For example, to output a file [name].js, you have to escape the [name] placeholder by adding backslashes between the brackets. So that [\name\] generates [name] instead of getting replaced with the name of the asset.

Example: [\id\] generates [id] instead of getting replaced with the id.

If using a function for this option, the function will be passed an object containing data for the substitutions in the table above. Substitutions will be applied to the returned string too. The passed object will have this type: (properties available depending on context)

type PathData = {
  hash: string;
  hashWithLength: (number) => string;
  chunk: Chunk | ChunkPathData;
  module: Module | ModulePathData;
  contentHashType: string;
  contentHash: string;
  contentHashWithLength: (number) => string;
  filename: string;
  url: string;
  runtime: string | SortableSet<string>;
  chunkGraph: ChunkGraph;
};
type ChunkPathData = {
  id: string | number;
  name: string;
  hash: string;
  hashWithLength: (number) => string;
  contentHash: Record<string, string>;
  contentHashWithLength: Record<string, (number) => string>;
};
type ModulePathData = {
  id: string | number;
  hash: string;
  hashWithLength: (number) => string;
};

output.globalObject

string = 'self'

When targeting a library, especially when libraryTarget is 'umd', this option indicates what global object will be used to mount the library. To make UMD build available on both browsers and Node.js, set output.globalObject option to 'this'. Defaults to self for Web-like targets.

The return value of your entry point will be assigned to the global object using the value of output.library.name. Depending on the value of the target option, the global object could change respectively, e.g., self, global, or globalThis.

For example:

webpack.config.js

module.exports = {
  // ...
  output: {
    library: 'myLib',
    libraryTarget: 'umd',
    filename: 'myLib.js',
    globalObject: 'this',
  },
};

output.hashDigest

string = 'hex'

The encoding to use when generating the hash. All encodings from Node.JS' hash.digest are supported. Using 'base64' for filenames might be problematic since it has the character / in its alphabet. Likewise 'latin1' could contain any character.

output.hashDigestLength

number = 20

The prefix length of the hash digest to use.

output.hashFunction

string = 'md4' function

The hashing algorithm to use. All functions from Node.JS' crypto.createHash are supported. Since 4.0.0-alpha2, the hashFunction can now be a constructor to a custom hash function. You can provide a non-crypto hash function for performance reasons.

module.exports = {
  //...
  output: {
    hashFunction: require('metrohash').MetroHash64,
  },
};

Make sure that the hashing function will have an update and digest methods available.

output.hashSalt

An optional salt to update the hash via Node.JS' hash.update.

output.hotUpdateChunkFilename

string = '[id].[fullhash].hot-update.js'

Customize the filenames of hot update chunks. See output.filename option for details on the possible values.

The only placeholders allowed here are [id] and [fullhash], the default being:

webpack.config.js

module.exports = {
  //...
  output: {
    hotUpdateChunkFilename: '[id].[fullhash].hot-update.js',
  },
};

output.hotUpdateGlobal

string

Only used when target is set to 'web', which uses JSONP for loading hot updates.

A JSONP function is used to asynchronously load hot-update chunks.

For details see output.chunkLoadingGlobal.

output.hotUpdateMainFilename

string = '[runtime].[fullhash].hot-update.json' function

Customize the main hot update filename. [fullhash] and [runtime] are available as placeholder.

output.iife

boolean = true

Tells webpack to add IIFE wrapper around emitted code.

module.exports = {
  //...
  output: {
    iife: true,
  },
};

output.ignoreBrowserWarnings

boolean = false

Hide warnings from the browser console in production. This option does not affect the terminal/console output.

webpack.config.js

module.exports = {
  //...
  output: {
    ignoreBrowserWarnings: true,
  },
};

output.importFunctionName

string = 'import'

The name of the native import() function. Can be used for polyfilling, e.g. with dynamic-import-polyfill.

webpack.config.js

module.exports = {
  //...
  output: {
    importFunctionName: '__import__',
  },
};

output.library

Output a library exposing the exports of your entry point.

• Type: string | string[] | object

Let's take a look at an example.

webpack.config.js

module.exports = {
  // …
  entry: './src/index.js',
  output: {
    library: 'MyLibrary',
  },
};

Say you have exported a function in your src/index.js entry:

export function hello(name) {
  console.log(`hello ${name}`);
}

Now the variable MyLibrary will be bound with the exports of your entry file, and here's how to consume the webpack bundled library:

<script src="https://example.org/path/to/my-library.js"></script>
<script>
  MyLibrary.hello('webpack');
</script>

In the above example, we're passing a single entry file to entry, however, webpack can accept many kinds of entry point, e.g., an array, or an object.

1. If you provide an array as the entry point, only the last one in the array will be exposed.

   module.exports = {
     // …
     entry: ['./src/a.js', './src/b.js'], // only exports in b.js will be exposed
     output: {
       library: 'MyLibrary',
     },
   };

2. If an object is provided as the entry point, all entries can be exposed using the array syntax of library:

   module.exports = {
     // …
     entry: {
       a: './src/a.js',
       b: './src/b.js',
     },
     output: {
       filename: '[name].js',
       library: ['MyLibrary', '[name]'], // name is a placeholder here
     },
   };

   Assuming that both a.js and b.js export a function hello, here's how to consume the libraries:

   <script src="https://example.org/path/to/a.js"></script>
   <script src="https://example.org/path/to/b.js"></script>
   <script>
     MyLibrary.a.hello('webpack');
     MyLibrary.b.hello('webpack');
   </script>

   See this example for more.

   Note that the above configuration won't work as expected if you're going to configure library options per entry point. Here is how to do it under each of your entries:

   module.exports = {
     // …
     entry: {
       main: {
         import: './src/index.js',
         library: {
           // all options under `output.library` can be used here
           name: 'MyLibrary',
           type: 'umd',
           umdNamedDefine: true,
         },
       },
       another: {
         import: './src/another.js',
         library: {
           name: 'AnotherLibrary',
           type: 'commonjs2',
         },
       },
     },
   };

output.library.amdContainer

Use a container(defined in global space) for calling define/require functions in an AMD module.

module.exports = {
  // …
  output: {
    library: {
      amdContainer: 'window["clientContainer"]',
      type: 'amd', // or 'amd-require'
    },
  },
};

Which will result in the following bundle:

window['clientContainer'].define(/*define args*/); // or 'amd-require' window['clientContainer'].require(/*require args*/);

output.library.name

module.exports = {
  // …
  output: {
    library: {
      name: 'MyLibrary',
    },
  },
};

Specify a name for the library.

• Type:

  string | string[] | {amd?: string, commonjs?: string, root?: string | string[]}

output.library.type

Configure how the library will be exposed.

• Type: string

  Types included by default are 'var', 'module', 'assign', 'assign-properties', 'this', 'window', 'self', 'global', 'commonjs', 'commonjs2', 'commonjs-module', 'commonjs-static', 'amd', 'amd-require', 'umd', 'umd2', 'jsonp' and 'system', but others might be added by plugins.

For the following examples, we'll use _entry_return_ to indicate the values returned by the entry point.

Expose a Variable

These options assign the return value of the entry point (e.g. whatever the entry point exported) to the name provided by output.library.name at whatever scope the bundle was included at.

type: 'var'

module.exports = {
  // …
  output: {
    library: {
      name: 'MyLibrary',
      type: 'var',
    },
  },
};

When your library is loaded, the return value of your entry point will be assigned to a variable:

var MyLibrary = _entry_return_;

// In a separate script with `MyLibrary` loaded…
MyLibrary.doSomething();

type: 'assign'

module.exports = {
  // …
  output: {
    library: {
      name: 'MyLibrary',
      type: 'assign',
    },
  },
};

This will generate an implied global which has the potential to reassign an existing value (use with caution):

MyLibrary = _entry_return_;

Be aware that if MyLibrary isn't defined earlier your library will be set in global scope.

type: 'assign-properties'

module.exports = {
  // …
  output: {
    library: {
      name: 'MyLibrary',
      type: 'assign-properties',
    },
  },
};

Similar to type: 'assign' but a safer option as it will reuse MyLibrary if it already exists:

// only create MyLibrary if it doesn't exist
MyLibrary = typeof MyLibrary === 'undefined' ? {} : MyLibrary;
// then copy the return value to MyLibrary
// similarly to what Object.assign does

// for instance, you export a `hello` function in your entry as follow
export function hello(name) {
  console.log(`Hello ${name}`);
}

// In another script with MyLibrary loaded
// you can run `hello` function like so
MyLibrary.hello('World');

Expose Via Object Assignment

These options assign the return value of the entry point (e.g. whatever the entry point exported) to a specific object under the name defined by output.library.name.

type: 'this'

module.exports = {
  // …
  output: {
    library: {
      name: 'MyLibrary',
      type: 'this',
    },
  },
};

The return value of your entry point will be assigned to this under the property named by output.library.name. The meaning of this is up to you:

this['MyLibrary'] = _entry_return_;

// In a separate script...
this.MyLibrary.doSomething();
MyLibrary.doSomething(); // if `this` is window

type: 'window'

module.exports = {
  // …
  output: {
    library: {
      name: 'MyLibrary',
      type: 'window',
    },
  },
};

The return value of your entry point will be assigned to the window object using the output.library.name value.

window['MyLibrary'] = _entry_return_;

window.MyLibrary.doSomething();

type: 'global'

module.exports = {
  // …
  output: {
    library: {
      name: 'MyLibrary',
      type: 'global',
    },
  },
};

The return value of your entry point will be assigned to the global object using the output.library.name value. Depending on the target value, the global object could change respectively, e.g., self, global or globalThis.

global['MyLibrary'] = _entry_return_;

global.MyLibrary.doSomething();

type: 'commonjs'

module.exports = {
  // …
  output: {
    library: {
      name: 'MyLibrary',
      type: 'commonjs',
    },
  },
};

The return value of your entry point will be assigned to the exports object using the output.library.name value. As the name implies, this is used in CommonJS environments.

exports['MyLibrary'] = _entry_return_;

require('MyLibrary').doSomething();

Module Definition Systems

These options will result in a bundle that comes with a complete header to ensure compatibility with various module systems. The output.library.name option will take on a different meaning under the following output.library.type options.

type: 'module'

module.exports = {
  // …
  experiments: {
    outputModule: true,
  },
  output: {
    library: {
      // do not specify a `name` here
      type: 'module',
    },
  },
};

Output ES Module.

However this feature is still experimental and not fully supported yet, so make sure to enable experiments.outputModule beforehand. In addition, you can track the development progress in this thread.

type: 'commonjs2'

module.exports = {
  // …
  output: {
    library: {
      // note there's no `name` here
      type: 'commonjs2',
    },
  },
};

The return value of your entry point will be assigned to the module.exports. As the name implies, this is used in Node.js (CommonJS) environments:

module.exports = _entry_return_;

require('MyLibrary').doSomething();

If we specify output.library.name with type: commmonjs2, the return value of your entry point will be assigned to the module.exports.[output.library.name].

type: 'commonjs-static'

module.exports = {
  // …
  output: {
    library: {
      // note there's no `name` here
      type: 'commonjs-static',
    },
  },
};

Individual exports will be set as properties on module.exports. The "static" in the name refers to the output being statically analysable, and thus named exports are importable into ESM via Node.js:

Input:

export function doSomething() {}

Output:

function doSomething() {}

// …

exports.doSomething = __webpack_exports__.doSomething;

Consumption (CommonJS):

const { doSomething } = require('./output.cjs'); // doSomething => [Function: doSomething]

Consumption (ESM):

import { doSomething } from './output.cjs'; // doSomething => [Function: doSomething]

type: 'amd'

This will expose your library as an AMD module.

AMD modules require that the entry chunk (e.g. the first script loaded by the <script> tag) be defined with specific properties, such as to define and require which is typically provided by RequireJS or any compatible loaders (such as almond). Otherwise, loading the resulting AMD bundle directly will result in an error like define is not defined.

With the following configuration...

module.exports = {
  //...
  output: {
    library: {
      name: 'MyLibrary',
      type: 'amd',
    },
  },
};

The generated output will be defined with the name "MyLibrary", i.e.:

define('MyLibrary', [], function () {
  return _entry_return_;
});

The bundle can be included as part of a script tag, and the bundle can be invoked like so:

require(['MyLibrary'], function (MyLibrary) {
  // Do something with the library...
});

If output.library.name is undefined, the following is generated instead.

define(function () {
  return _entry_return_;
});

This bundle will not work as expected, or not work at all (in the case of the almond loader) if loaded directly with a <script> tag. It will only work through a RequireJS compatible asynchronous module loader through the actual path to that file, so in this case, the output.path and output.filename may become important for this particular setup if these are exposed directly on the server.

type: 'amd-require'

module.exports = {
  //...
  output: {
    library: {
      name: 'MyLibrary',
      type: 'amd-require',
    },
  },
};

This packages your output with an immediately executed AMD require(dependencies, factory) wrapper.

The 'amd-require' type allows for the use of AMD dependencies without needing a separate later invocation. As with the 'amd' type, this depends on the appropriate require function being available in the environment in which the webpack output is loaded.

With this type, the library name can't be used.

type: 'umd'

This exposes your library under all the module definitions, allowing it to work with CommonJS, AMD, and as global variable. Take a look at the UMD Repository to learn more.

In this case, you need the library.name property to name your module:

module.exports = {
  //...
  output: {
    library: {
      name: 'MyLibrary',
      type: 'umd',
    },
  },
};

And finally the output is:

(function webpackUniversalModuleDefinition(root, factory) {
  if (typeof exports === 'object' && typeof module === 'object')
    module.exports = factory();
  else if (typeof define === 'function' && define.amd) define([], factory);
  else if (typeof exports === 'object') exports['MyLibrary'] = factory();
  else root['MyLibrary'] = factory();
})(global, function () {
  return _entry_return_;
});

Note that omitting library.name will result in the assignment of all properties returned by the entry point be assigned directly to the root object, as documented under the object assignment section. Example:

module.exports = {
  //...
  output: {
    libraryTarget: 'umd',
  },
};

The output will be:

(function webpackUniversalModuleDefinition(root, factory) {
  if (typeof exports === 'object' && typeof module === 'object')
    module.exports = factory();
  else if (typeof define === 'function' && define.amd) define([], factory);
  else {
    var a = factory();
    for (var i in a) (typeof exports === 'object' ? exports : root)[i] = a[i];
  }
})(global, function () {
  return _entry_return_;
});

You may specify an object for library.name for differing names per targets:

module.exports = {
  //...
  output: {
    library: {
      name: {
        root: 'MyLibrary',
        amd: 'my-library',
        commonjs: 'my-common-library',
      },
      type: 'umd',
    },
  },
};

type: 'system'

This will expose your library as a System.register module. This feature was first released in webpack 4.30.0.

System modules require that a global variable System is present in the browser when the webpack bundle is executed. Compiling to System.register format allows you to System.import('/bundle.js') without additional configuration and has your webpack bundle loaded into the System module registry.

module.exports = {
  //...
  output: {
    library: {
      type: 'system',
    },
  },
};

Output:

System.register([], function (__WEBPACK_DYNAMIC_EXPORT__, __system_context__) {
  return {
    execute: function () {
      // ...
    },
  };
});

By adding output.library.name to configuration in addition to having output.library.type set to system, the output bundle will have the library name as an argument to System.register:

System.register(
  'MyLibrary',
  [],
  function (__WEBPACK_DYNAMIC_EXPORT__, __system_context__) {
    return {
      execute: function () {
        // ...
      },
    };
  }
);

Other Types

type: 'jsonp'

module.exports = {
  // …
  output: {
    library: {
      name: 'MyLibrary',
      type: 'jsonp',
    },
  },
};

This will wrap the return value of your entry point into a jsonp wrapper.

MyLibrary(_entry_return_);

The dependencies for your library will be defined by the externals config.

output.library.export

Specify which export should be exposed as a library.

• Type: string | string[]

It is undefined by default, which will export the whole (namespace) object. The examples below demonstrate the effect of this configuration when using output.library.type: 'var'.

module.exports = {
  output: {
    library: {
      name: 'MyLibrary',
      type: 'var',
      export: 'default',
    },
  },
};

The default export of your entry point will be assigned to the library name:

// if your entry has a default export
var MyLibrary = _entry_return_.default;

You can pass an array to output.library.export as well, it will be interpreted as a path to a module to be assigned to the library name:

module.exports = {
  output: {
    library: {
      name: 'MyLibrary',
      type: 'var',
      export: ['default', 'subModule'],
    },
  },
};

And here's the library code:

var MyLibrary = _entry_return_.default.subModule;

output.library.auxiliaryComment

Add a comment in the UMD wrapper.

• Type: string | { amd?: string, commonjs?: string, commonjs2?: string, root?: string }

To insert the same comment for each umd type, set auxiliaryComment to a string:

module.exports = {
  // …
  mode: 'development',
  output: {
    library: {
      name: 'MyLibrary',
      type: 'umd',
      auxiliaryComment: 'Test Comment',
    },
  },
};

which will yield the following:

(function webpackUniversalModuleDefinition(root, factory) {
  //Test Comment
  if (typeof exports === 'object' && typeof module === 'object')
    module.exports = factory();
  //Test Comment
  else if (typeof define === 'function' && define.amd) define([], factory);
  //Test Comment
  else if (typeof exports === 'object') exports['MyLibrary'] = factory();
  //Test Comment
  else root['MyLibrary'] = factory();
})(self, function () {
  return _entry_return_;
});

For fine-grained control, pass an object:

module.exports = {
  // …
  mode: 'development',
  output: {
    library: {
      name: 'MyLibrary',
      type: 'umd',
      auxiliaryComment: {
        root: 'Root Comment',
        commonjs: 'CommonJS Comment',
        commonjs2: 'CommonJS2 Comment',
        amd: 'AMD Comment',
      },
    },
  },
};

output.library.umdNamedDefine

boolean

When using output.library.type: "umd", setting output.library.umdNamedDefine to true will name the AMD module of the UMD build. Otherwise, an anonymous define is used.

module.exports = {
  //...
  output: {
    library: {
      name: 'MyLibrary',
      type: 'umd',
      umdNamedDefine: true,
    },
  },
};

The AMD module will be:

define('MyLibrary', [], factory);

output.libraryExport

string [string]

Configure which module or modules will be exposed via the libraryTarget. It is undefined by default, same behaviour will be applied if you set libraryTarget to an empty string e.g. '' it will export the whole (namespace) object. The examples below demonstrate the effect of this configuration when using libraryTarget: 'var'.

The following configurations are supported:

libraryExport: 'default' - The default export of your entry point will be assigned to the library target:

// if your entry has a default export of `MyDefaultModule`
var MyDefaultModule = _entry_return_.default;

libraryExport: 'MyModule' - The specified module will be assigned to the library target:

var MyModule = _entry_return_.MyModule;

libraryExport: ['MyModule', 'MySubModule'] - The array is interpreted as a path to a module to be assigned to the library target:

var MySubModule = _entry_return_.MyModule.MySubModule;

With the libraryExport configurations specified above, the resulting libraries could be utilized as such:

MyDefaultModule.doSomething();
MyModule.doSomething();
MySubModule.doSomething();

output.libraryTarget

string = 'var'

Configure how the library will be exposed. Any one of the following options can be used. Please note that this option works in conjunction with the value assigned to output.library. For the following examples, it is assumed that the value of output.library is configured as MyLibrary.

Expose a Variable

These options assign the return value of the entry point (e.g. whatever the entry point exported) to the name provided by output.library at whatever scope the bundle was included at.

libraryTarget: 'var'

When your library is loaded, the return value of your entry point will be assigned to a variable:

var MyLibrary = _entry_return_;

// In a separate script...
MyLibrary.doSomething();

libraryTarget: 'assign'

This will generate an implied global which has the potential to reassign an existing value (use with caution):

MyLibrary = _entry_return_;

Be aware that if MyLibrary isn't defined earlier your library will be set in the global scope.

libraryTarget: 'assign-properties'

Copy the return value to a target object if it exists, otherwise create the target object first:

// create the target object if it doesn't exist
MyLibrary = typeof MyLibrary === 'undefined' ? {} : MyLibrary;
// then copy the return value to MyLibrary
// similarly to what Object.assign does

// for instance, you export a `hello` function in your entry as follow
export function hello(name) {
  console.log(`Hello ${name}`);
}

// In another script running MyLibrary
// you can run `hello` function like so
MyLibrary.hello('World');

Expose Via Object Assignment

These options assign the return value of the entry point (e.g. whatever the entry point exported) to a specific object under the name defined by output.library.

If output.library is not assigned a non-empty string, the default behavior is that all properties returned by the entry point will be assigned to the object as defined for the particular output.libraryTarget, via the following code fragment:

(function (e, a) {
  for (var i in a) {
    e[i] = a[i];
  }
})(output.libraryTarget, _entry_return_);

libraryTarget: 'this'

The return value of your entry point will be assigned to this under the property named by output.library. The meaning of this is up to you:

this['MyLibrary'] = _entry_return_;

// In a separate script...
this.MyLibrary.doSomething();
MyLibrary.doSomething(); // if this is window

libraryTarget: 'window'

The return value of your entry point will be assigned to the window object using the output.library value.

window['MyLibrary'] = _entry_return_;

window.MyLibrary.doSomething();

libraryTarget: 'global'

The return value of your entry point will be assigned to the global object using the output.library value.

global['MyLibrary'] = _entry_return_;

global.MyLibrary.doSomething();

libraryTarget: 'commonjs'

The return value of your entry point will be assigned to the exports object using the output.library value. As the name implies, this is used in CommonJS environments.

exports['MyLibrary'] = _entry_return_;

require('MyLibrary').doSomething();

Module Definition Systems

These options will result in a bundle that comes with a complete header to ensure compatibility with various module systems. The output.library option will take on a different meaning under the following output.libraryTarget options.

libraryTarget: 'module'

Output ES Module. Make sure to enable experiments.outputModule beforehand.

Note that this feature is not fully supported yet, please track the progress in this thread.

libraryTarget: 'commonjs2'

The return value of your entry point will be assigned to the module.exports. As the name implies, this is used in CommonJS environments:

module.exports = _entry_return_;

require('MyLibrary').doSomething();

Note that output.library can't be used with this particular output.libraryTarget, for further details, please read this issue.

libraryTarget: 'amd'

This will expose your library as an AMD module.

AMD modules require that the entry chunk (e.g. the first script loaded by the <script> tag) be defined with specific properties, such as to define and require which is typically provided by RequireJS or any compatible loaders (such as almond). Otherwise, loading the resulting AMD bundle directly will result in an error like define is not defined.

With the following configuration...

module.exports = {
  //...
  output: {
    library: 'MyLibrary',
    libraryTarget: 'amd',
  },
};

The generated output will be defined with the name "MyLibrary", i.e.

define('MyLibrary', [], function () {
  return _entry_return_;
});

The bundle can be included as part of a script tag, and the bundle can be invoked like so:

require(['MyLibrary'], function (MyLibrary) {
  // Do something with the library...
});

If output.library is undefined, the following is generated instead.

define([], function () {
  return _entry_return_;
});

This bundle will not work as expected, or not work at all (in the case of the almond loader) if loaded directly with a <script> tag. It will only work through a RequireJS compatible asynchronous module loader through the actual path to that file, so in this case, the output.path and output.filename may become important for this particular setup if these are exposed directly on the server.

libraryTarget: 'amd-require'

This packages your output with an immediately executed AMD require(dependencies, factory) wrapper.

The 'amd-require' target allows for the use of AMD dependencies without needing a separate later invocation. As with the 'amd' target, this depends on the appropriate require function being available in the environment in which the webpack output is loaded.

With this target, the library name is ignored.

libraryTarget: 'umd'

This exposes your library under all the module definitions, allowing it to work with CommonJS, AMD and as a global variable. Take a look at the UMD Repository to learn more.

In this case, you need the library property to name your module:

module.exports = {
  //...
  output: {
    library: 'MyLibrary',
    libraryTarget: 'umd',
  },
};

And finally the output is:

(function webpackUniversalModuleDefinition(root, factory) {
  if (typeof exports === 'object' && typeof module === 'object')
    module.exports = factory();
  else if (typeof define === 'function' && define.amd) define([], factory);
  else if (typeof exports === 'object') exports['MyLibrary'] = factory();
  else root['MyLibrary'] = factory();
})(typeof self !== 'undefined' ? self : this, function () {
  return _entry_return_;
});

Note that omitting the library will result in the assignment of all properties returned by the entry point be assigned directly to the root object, as documented under the object assignment section. Example:

module.exports = {
  //...
  output: {
    libraryTarget: 'umd',
  },
};

The output will be:

(function webpackUniversalModuleDefinition(root, factory) {
  if (typeof exports === 'object' && typeof module === 'object')
    module.exports = factory();
  else if (typeof define === 'function' && define.amd) define([], factory);
  else {
    var a = factory();
    for (var i in a) (typeof exports === 'object' ? exports : root)[i] = a[i];
  }
})(typeof self !== 'undefined' ? self : this, function () {
  return _entry_return_;
});

Since webpack 3.1.0, you may specify an object for library for differing names per targets:

module.exports = {
  //...
  output: {
    library: {
      root: 'MyLibrary',
      amd: 'my-library',
      commonjs: 'my-common-library',
    },
    libraryTarget: 'umd',
  },
};

libraryTarget: 'system'

This will expose your library as a System.register module. This feature was first released in webpack 4.30.0.

System modules require that a global variable System is present in the browser when the webpack bundle is executed. Compiling to System.register format allows you to System.import('/bundle.js') without additional configuration and has your webpack bundle loaded into the System module registry.

module.exports = {
  //...
  output: {
    libraryTarget: 'system',
  },
};

Output:

System.register([], function (_export) {
  return {
    setters: [],
    execute: function () {
      // ...
    },
  };
});

By adding output.library to configuration in addition to having output.libraryTarget set to system, the output bundle will have the library name as an argument to System.register:

System.register('my-library', [], function (_export) {
  return {
    setters: [],
    execute: function () {
      // ...
    },
  };
});

You can access SystemJS context via __system_context__:

// Log the URL of the current SystemJS module
console.log(__system_context__.meta.url);

// Import a SystemJS module, with the current SystemJS module's url as the parentUrl
__system_context__.import('./other-file.js').then((m) => {
  console.log(m);
});

Other Targets

libraryTarget: 'jsonp'

This will wrap the return value of your entry point into a jsonp wrapper.

MyLibrary(_entry_return_);

The dependencies for your library will be defined by the externals config.

output.module

boolean = false

Output JavaScript files as module type. Disabled by default as it's an experimental feature.

When enabled, webpack will set output.iife to false, output.scriptType to 'module' and terserOptions.module to true internally.

If you're using webpack to compile a library to be consumed by others, make sure to set output.libraryTarget to 'module' when output.module is true.

module.exports = {
  //...
  experiments: {
    outputModule: true,
  },
  output: {
    module: true,
  },
};

output.path

string = path.join(process.cwd(), 'dist')

The output directory as an absolute path.

webpack.config.js

const path = require('path');

module.exports = {
  //...
  output: {
    path: path.resolve(__dirname, 'dist/assets'),
  },
};

Note that [fullhash] in this parameter will be replaced with a hash of the compilation. See the Caching guide for details.

output.pathinfo

boolean=true string: 'verbose'

Tells webpack to include comments in bundles with information about the contained modules. This option defaults to true in development and false in production mode respectively. 'verbose' shows more information like exports, runtime requirements and bailouts.

webpack.config.js

module.exports = {
  //...
  output: {
    pathinfo: true,
  },
};

output.publicPath

• Type:

  • function

  • string

    output.publicPath defaults to 'auto' with web and web-worker targets, see this guide for its use cases.

This is an important option when using on-demand-loading or loading external resources like images, files, etc. If an incorrect value is specified you'll receive 404 errors while loading these resources.

This option specifies the public URL of the output directory when referenced in a browser. A relative URL is resolved relative to the HTML page (or <base> tag). Server-relative URLs, protocol-relative URLs or absolute URLs are also possible and sometimes required, i. e. when hosting assets on a CDN.

The value of the option is prefixed to every URL created by the runtime or loaders. Because of this the value of this option ends with / in most cases.

A rule to consider: The URL of your output.path from the view of the HTML page.

webpack.config.js

const path = require('path');

module.exports = {
  //...
  output: {
    path: path.resolve(__dirname, 'public/assets'),
    publicPath: 'https://cdn.example.com/assets/',
  },
};

For this configuration:

webpack.config.js

module.exports = {
  //...
  output: {
    publicPath: '/assets/',
    chunkFilename: '[id].chunk.js',
  },
};

A request to a chunk will look like /assets/4.chunk.js.

A loader outputting HTML might emit something like this:

<link href="/assets/spinner.gif" />

or when loading an image in CSS:

background-image: url(/assets/spinner.gif);

The webpack-dev-server also takes a hint from publicPath, using it to determine where to serve the output files from.

Note that [fullhash] in this parameter will be replaced with a hash of the compilation. See the Caching guide for details.

Examples:

module.exports = {
  //...
  output: {
    // One of the below
    publicPath: 'auto', // It automatically determines the public path from either `import.meta.url`, `document.currentScript`, `<script />` or `self.location`.
    publicPath: 'https://cdn.example.com/assets/', // CDN (always HTTPS)
    publicPath: '//cdn.example.com/assets/', // CDN (same protocol)
    publicPath: '/assets/', // server-relative
    publicPath: 'assets/', // relative to HTML page
    publicPath: '../assets/', // relative to HTML page
    publicPath: '', // relative to HTML page (same directory)
  },
};

In cases where the publicPath of output files can't be known at compile time, it can be left blank and set dynamically at runtime in the entry file using the free variable __webpack_public_path__.

__webpack_public_path__ = myRuntimePublicPath;

// rest of your application entry

See this discussion for more information on __webpack_public_path__.

output.scriptType

string: 'module' | 'text/javascript' boolean = false

This option allows loading asynchronous chunks with a custom script type, such as <script type="module" ...>.

module.exports = {
  //...
  output: {
    scriptType: 'module',
  },
};

output.sourceMapFilename

string = '[file].map[query]'

Configure how source maps are named. Only takes effect when devtool is set to 'source-map', which writes an output file.

The [name], [id], [fullhash] and [chunkhash] substitutions from output.filename can be used. In addition to those, you can use substitutions listed under Filename-level in Template strings.

output.sourcePrefix

string = ''

Change the prefix for each line in the output bundles.

webpack.config.js

module.exports = {
  //...
  output: {
    sourcePrefix: '\t',
  },
};

output.strictModuleErrorHandling

Handle error in module loading as per EcmaScript Modules spec at a performance cost.

• Type: boolean
• Available: 5.25.0+

module.exports = {
  //...
  output: {
    strictModuleErrorHandling: true,
  },
};

output.strictModuleExceptionHandling

boolean = false

Tell webpack to remove a module from the module instance cache (require.cache) if it throws an exception when it is required.

It defaults to false for performance reasons.

When set to false, the module is not removed from cache, which results in the exception getting thrown only on the first require call (making it incompatible with node.js).

For instance, consider module.js:

throw new Error('error');

With strictModuleExceptionHandling set to false, only the first require throws an exception:

// with strictModuleExceptionHandling = false
require('module'); // <- throws
require('module'); // <- doesn't throw

Instead, with strictModuleExceptionHandling set to true, all requires of this module throw an exception:

// with strictModuleExceptionHandling = true
require('module'); // <- throws
require('module'); // <- also throws

output.trustedTypes

boolean = false string object

Controls Trusted Types compatibility. When enabled, webpack will detect Trusted Types support and, if they are supported, use Trusted Types policies to create script URLs it loads dynamically. Use when the application runs under a require-trusted-types-for Content Security Policy directive.

It defaults to false (no compatibility, script URLs are strings).

• When set to true, webpack will use output.uniqueName as the Trusted Types policy name.
• When set to a non-empty string, its value will be used as a policy name.
• When set to an object, the policy name is taken from the object's policyName property.

webpack.config.js

module.exports = {
  //...
  output: {
    //...
    trustedTypes: {
      policyName: 'my-application#webpack',
    },
  },
};

output.trustedTypes.onPolicyCreationFailure

string = 'stop': 'continue' | 'stop'

Determine whether to proceed with loading in anticipation that require-trusted-types-for 'script' has not been enforced or to immediately fail when the call to trustedTypes.createPolicy(...) fails due to the policy name being absent from the CSP trusted-types list or being a duplicate.

module.exports = {
  //...
  output: {
    //...
    trustedTypes: {
      policyName: 'my-application#webpack',
      onPolicyCreationFailure: 'continue',
    },
  },
};

output.umdNamedDefine

boolean

When using libraryTarget: "umd", setting output.umdNamedDefine to true will name the AMD module of the UMD build. Otherwise an anonymous define is used.

module.exports = {
  //...
  output: {
    umdNamedDefine: true,
  },
};

output.uniqueName

string

A unique name of the webpack build to avoid multiple webpack runtimes to conflict when using globals. It defaults to output.library name or the package name from package.json in the context, if both aren't found, it is set to an ''.

output.uniqueName will be used to generate unique globals for:

• output.chunkLoadingGlobal

webpack.config.js

module.exports = {
  // ...
  output: {
    uniqueName: 'my-package-xyz',
  },
};

output.wasmLoading

boolean = false string

Option to set the method of loading WebAssembly Modules. Methods included by default are 'fetch' (web/WebWorker), 'async-node' (Node.js), but others might be added by plugins.

The default value can be affected by different target:

• Defaults to 'fetch' if target is set to 'web', 'webworker', 'electron-renderer' or 'node-webkit'.
• Defaults to 'async-node' if target is set to 'node', 'async-node', 'electron-main' or 'electron-preload'.

module.exports = {
  //...
  output: {
    wasmLoading: 'fetch',
  },
};

output.workerChunkLoading

string: 'require' | 'import-scripts' | 'async-node' | 'import' | 'universal' boolean: false

The new option workerChunkLoading controls the chunk loading of workers.

webpack.config.js

module.exports = {
  //...
  output: {
    workerChunkLoading: false,
  },
};

output.workerPublicPath

string

Set a public path for Worker, defaults to value of output.publicPath. Only use this option if your worker scripts are located in a different path from your other scripts.

webpack.config.js

module.exports = {
  //...
  output: {
    workerPublicPath: '/workerPublicPath2/',
  },
};

Module

These options determine how the different types of modules within a project will be treated.

module.defaultRules

An array of rules applied by default for modules.

See source code for details.

module.exports = {
  module: {
    defaultRules: [
      '...', // you can use "..." to reference those rules applied by webpack by default
    ],
  },
};

Starting with webpack 5.87.0, falsy values including 0, "", false, null and undefined are allowed to pass to module.defaultRules to conditionally disable specific rules.

module.exports = {
  module: {
    defaultRules: [
      false &&
        {
          // this rule will be disabled
        },
    ],
  },
};

module.generator

It's possible to configure all generators' options in one place with a module.generator.

webpack.config.js

module.exports = {
  module: {
    generator: {
      asset: {
        // Generator options for asset modules

        // Customize publicPath for asset modules, available since webpack 5.28.0
        publicPath: 'https://cdn/assets/',

        // Emit the asset in the specified folder relative to 'output.path', available since webpack 5.67.0
        outputPath: 'cdn-assets/',
      },
      'asset/inline': {
        // Generator options for asset/inline modules
      },
      'asset/resource': {
        // Generator options for asset/resource modules

        // Customize publicPath for asset/resource modules, available since webpack 5.28.0
        publicPath: 'https://cdn/assets/',

        // Emit the asset in the specified folder relative to 'output.path', available since webpack 5.67.0
        outputPath: 'cdn-assets/',
      },
      javascript: {
        // No generator options are supported for this module type yet
      },
      'javascript/auto': {
        // ditto
      },
      'javascript/dynamic': {
        // ditto
      },
      'javascript/esm': {
        // ditto
      },
      // others…
    },
  },
};

module.parser

Similar to the module.generator, you can configure all parsers' options in one place with a module.parser.

webpack.config.js

module.exports = {
  module: {
    parser: {
      asset: {
        // Parser options for asset modules
      },
      'asset/inline': {
        // No parser options are supported for this module type yet
      },
      'asset/resource': {
        // ditto
      },
      'asset/source': {
        // ditto
      },
      javascript: {
        // Parser options for javascript modules
        // e.g, enable parsing of require.ensure syntax
        requireEnsure: true,
      },
      'javascript/auto': {
        // ditto
      },
      'javascript/dynamic': {
        // ditto
      },
      'javascript/esm': {
        // ditto
      },
      // others…
    },
  },
};

module.parser.javascript

Configure options for JavaScript parser.

module.exports = {
  module: {
    parser: {
      javascript: {
        // ...
        commonjsMagicComments: true,
      },
    },
  },
};

It's allowed to configure those options in Rule.parser as well to target specific modules.

module.parser.javascript.commonjsMagicComments

Enable magic comments support for CommonJS.

• Type: boolean

• Available: 5.17.0+

• Example:

  module.exports = {
    module: {
      parser: {
        javascript: {
          commonjsMagicComments: true,
        },
      },
    },
  };

Note that only webpackIgnore comment is supported at the moment:

const x = require(/* webpackIgnore: true */ 'x');

module.parser.javascript.dynamicImportFetchPriority

Specify the global fetchPriority for dynamic import.

• Type: 'low' | 'high' | 'auto' | false

• Available: 5.87.0+

• Example:

  module.exports = {
    module: {
      parser: {
        javascript: {
          dynamicImportFetchPriority: 'high',
        },
      },
    },
  };

module.parser.javascript.dynamicImportMode

Specifies global mode for dynamic import.

• Type: 'eager' | 'weak' | 'lazy' | 'lazy-once'

• Available: 5.73.0+

• Example:

  module.exports = {
    module: {
      parser: {
        javascript: {
          dynamicImportMode: 'lazy',
        },
      },
    },
  };

module.parser.javascript.dynamicImportPrefetch

Specifies global prefetch for dynamic import.

• Type: number | boolean

• Available: 5.73.0+

• Example:

  module.exports = {
    module: {
      parser: {
        javascript: {
          dynamicImportPrefetch: false,
        },
      },
    },
  };

module.parser.javascript.dynamicImportPreload

Specifies global preload for dynamic import.

• Type: number | boolean

• Available: 5.73.0+

• Example:

  module.exports = {
    module: {
      parser: {
        javascript: {
          dynamicImportPreload: false,
        },
      },
    },
  };

module.parser.javascript.exportsPresence

Specifies the behavior of invalid export names in \"import ... from ...\" and \"export ... from ...\".

• Type: 'error' | 'warn' | 'auto' | false

• Available: 5.62.0+

• Example:

  module.exports = {
    module: {
      parser: {
        javascript: {
          exportsPresence: 'error',
        },
      },
    },
  };

module.parser.javascript.importExportsPresence

Specifies the behavior of invalid export names in \"import ... from ...\".

• Type: 'error' | 'warn' | 'auto' | false

• Available: 5.62.0+

• Example:

  module.exports = {
    module: {
      parser: {
        javascript: {
          importExportsPresence: 'error',
        },
      },
    },
  };

module.parser.javascript.importMeta

Enable or disable evaluating import.meta.

• Type: boolean = true

• Available: 5.68.0+

• Example:

  module.exports = {
    module: {
      parser: {
        javascript: {
          importMeta: false,
        },
      },
    },
  };

module.parser.javascript.importMetaContext

Enable/disable evaluating import.meta.webpackContext.

• Type: boolean

• Available: 5.70.0+

• Example:

  module.exports = {
    module: {
      parser: {
        javascript: {
          importMetaContext: true,
        },
      },
    },
  };

module.parser.javascript.reexportExportsPresence

Specifies the behavior of invalid export names in \"export ... from ...\". This might be useful to disable during the migration from \"export ... from ...\" to \"export type ... from ...\" when reexporting types in TypeScript.

• Type: 'error' | 'warn' | 'auto' | false

• Available: 5.62.0+

• Example:

  module.exports = {
    module: {
      parser: {
        javascript: {
          reexportExportsPresence: 'error',
        },
      },
    },
  };

module.parser.javascript.url

Enable parsing of new URL() syntax.

• Type: boolean = true | 'relative'

• Example:

  module.exports = {
    module: {
      parser: {
        javascript: {
          url: false, // disable parsing of `new URL()` syntax
        },
      },
    },
  };

The 'relative' value for module.parser.javascript.url is available since webpack 5.23.0. When used, webpack would generate relative URLs for new URL() syntax, i.e., there's no base URL included in the result URL:

<!-- with 'relative' -->
<img src="c43188443804f1b1f534.svg" />

<!-- without 'relative' -->
<img src="file:///path/to/project/dist/c43188443804f1b1f534.svg" />

1. This is useful for SSR (Server side rendering) when base URL is not known by server (and it saves a few bytes). To be identical it must also be used for the client build.
2. Also for static site generators, mini-css-plugin and html-plugin, etc. where server side rendering is commonly needed.

module.noParse

RegExp [RegExp] function(resource) string [string]

Prevent webpack from parsing any files matching the given regular expression(s). Ignored files should not have calls to import, require, define or any other importing mechanism. This can boost build performance when ignoring large libraries.

webpack.config.js

module.exports = {
  //...
  module: {
    noParse: /jquery|lodash/,
  },
};

module.exports = {
  //...
  module: {
    noParse: (content) => /jquery|lodash/.test(content),
  },
};

module.unsafeCache

boolean function (module)

Cache the resolution of module requests. There are a couple of defaults for module.unsafeCache:

• false if cache is disabled.
• true if cache is enabled and the module appears to come from node modules, false otherwise.

webpack.config.js

module.exports = {
  //...
  module: {
    unsafeCache: false,
  },
};

module.rules

(Rule | undefined | null | false | "" | 0 | "...")[]

An array of Rules which are matched to requests when modules are created. These rules can modify how the module is created. They can apply loaders to the module, or modify the parser.

As of webpack 5.87.0, falsy values such as false, undefined, null and 0 can be used to conditionally disable a rule.

Rule

object

A Rule can be separated into three parts — Conditions, Results and nested Rules.

Rule Conditions

There are two input values for the conditions:

1. The resource: An absolute path to the file requested. It's already resolved according to the resolve rules.

2. The issuer: An absolute path to the file of the module which requested the resource. It's the location of the import.

Example: When we import './style.css' within app.js, the resource is /path/to/style.css and the issuer is /path/to/app.js.

In a Rule the properties test, include, exclude and resource are matched with the resource and the property issuer is matched with the issuer.

When using multiple conditions, all conditions must match.

Rule results

Rule results are used only when the Rule condition matches.

There are two output values of a Rule:

1. Applied loaders: An array of loaders applied to the resource.
2. Parser options: An options object which should be used to create the parser for this module.

These properties affect the loaders: loader, options, use.

For compatibility also these properties: query, loaders.

The enforce property affects the loader category. Whether it's a normal, pre- or post- loader.

The parser property affects the parser options.

Nested rules

Nested rules can be specified under the properties rules and oneOf.

These rules are evaluated only when the parent Rule condition matches. Each nested rule can contain its own conditions.

The order of evaluation is as follows:

1. The parent rule
2. rules
3. oneOf

Rule.enforce

string

Possible values: 'pre' | 'post'

Specifies the category of the loader. No value means normal loader.

There is also an additional category "inlined loader" which are loaders applied inline of the import/require.

There are two phases that all loaders enter one after the other:

1. Pitching phase: the pitch method on loaders is called in the order post, inline, normal, pre. See Pitching Loader for details.
2. Normal phase: the normal method on loaders is executed in the order pre, normal, inline, post. Transformation on the source code of a module happens in this phase.

All normal loaders can be omitted (overridden) by prefixing ! in the request.

All normal and pre loaders can be omitted (overridden) by prefixing -! in the request.

All normal, post and pre loaders can be omitted (overridden) by prefixing !! in the request.

// Disable normal loaders
import { a } from '!./file1.js';

// Disable preloaders and normal loaders
import { b } from '-!./file2.js';

// Disable all loaders
import { c } from '!!./file3.js';

Inline loaders and ! prefixes should not be used as they are non-standard. They may be used by loader generated code.

Rule.exclude

Exclude all modules matching any of these conditions. If you supply a Rule.exclude option, you cannot also supply a Rule.resource. See Rule.resource and Condition.exclude for details.

Rule.include

Include all modules matching any of these conditions. If you supply a Rule.include option, you cannot also supply a Rule.resource. See Rule.resource and Condition.include for details.

Rule.issuer

A Condition to match against the module that issued the request. In the following example, the issuer for the a.js request would be the path to the index.js file.

index.js

import A from './a.js';

This option can be used to apply loaders to the dependencies of a specific module or set of modules.

Rule.issuerLayer

Allows to filter/match by layer of the issuer.

webpack.config.js

module.exports = {
  // ...
  module: {
    rules: [
      {
        issuerLayer: 'other-layer',
      },
    ],
  },
};

Rule.layer

string

Specify the layer in which the module should be placed in. A group of modules could be united in one layer which could then be used in split chunks, stats or entry options.

webpack.config.js

module.exports = {
  // ...
  module: {
    rules: [
      {
        test: /module-layer-change/,
        layer: 'layer',
      },
    ],
  },
};

Rule.loader

Rule.loader is a shortcut to Rule.use: [ { loader } ]. See Rule.use and UseEntry.loader for details.

Rule.loaders

Rule.loaders is an alias to Rule.use. See Rule.use for details.

Rule.mimetype

You can match config rules to data uri with mimetype.

webpack.config.js

module.exports = {
  // ...
  module: {
    rules: [
      {
        mimetype: 'application/json',
        type: 'json',
      },
    ],
  },
};

application/json, text/javascript, application/javascript, application/node and application/wasm are already included by default as mimetype.

Rule.oneOf

An array of Rules from which only the first matching Rule is used when the Rule matches.

webpack.config.js

module.exports = {
  //...
  module: {
    rules: [
      {
        test: /\.css$/,
        oneOf: [
          {
            resourceQuery: /inline/, // foo.css?inline
            type: 'asset/inline',
          },
          {
            resourceQuery: /external/, // foo.css?external
            type: 'asset/resource',
          },
        ],
      },
    ],
  },
};

Rule.options / Rule.query

Rule.options and Rule.query are shortcuts to Rule.use: [ { options } ]. See Rule.use and UseEntry.options for details.

Rule.parser

An object with parser options. All applied parser options are merged.

Parsers may inspect these options and disable or reconfigure themselves accordingly. Most of the default plugins interpret the values as follows:

• Setting the option to false disables the parser.
• Setting the option to true or leaving it undefined enables the parser.

However, parser plugins may accept more than only a boolean. For example, the internal NodeStuffPlugin can accept an object instead of true to add additional options for a particular Rule.

Examples (parser options by the default plugins):

module.exports = {
  //...
  module: {
    rules: [
      {
        //...
        parser: {
          amd: false, // disable AMD
          commonjs: false, // disable CommonJS
          system: false, // disable SystemJS
          harmony: false, // disable ES2015 Harmony import/export
          requireInclude: false, // disable require.include
          requireEnsure: false, // disable require.ensure
          requireContext: false, // disable require.context
          browserify: false, // disable special handling of Browserify bundles
          requireJs: false, // disable requirejs.*
          node: false, // disable __dirname, __filename, module, require.extensions, require.main, etc.
          commonjsMagicComments: false, // disable magic comments support for CommonJS
          node: {}, // reconfigure node layer on module level
          worker: ['default from web-worker', '...'], // Customize the WebWorker handling for javascript files, "..." refers to the defaults.
        },
      },
    ],
  },
};

If Rule.type is an asset then Rules.parser option may be an object or a function that describes a condition whether to encode file contents to Base64 or emit it as a separate file into the output directory.

If Rule.type is an asset or asset/inline then Rule.generator option may be an object that describes the encoding of the module source or a function that encodes module's source by a custom algorithm.

See Asset Modules guide for additional information and use cases.

Rule.parser.dataUrlCondition

object = { maxSize number = 8096 } function (source, { filename, module }) => boolean

If a module source size is less than maxSize then module will be injected into the bundle as a Base64-encoded string, otherwise module file will be emitted into the output directory.

webpack.config.js

module.exports = {
  //...
  module: {
    rules: [
      {
        //...
        parser: {
          dataUrlCondition: {
            maxSize: 4 * 1024,
          },
        },
      },
    ],
  },
};

When a function is given, returning true tells webpack to inject the module into the bundle as Base64-encoded string, otherwise module file will be emitted into the output directory.

webpack.config.js

module.exports = {
  //...
  module: {
    rules: [
      {
        //...
        parser: {
          dataUrlCondition: (source, { filename, module }) => {
            const content = source.toString();
            return content.includes('some marker');
          },
        },
      },
    ],
  },
};

Rule.generator

Rule.generator.dataUrl

object = { encoding string = 'base64' | false, mimetype string = undefined | false } function (content, { filename, module }) => string

When Rule.generator.dataUrl is used as an object, you can configure two properties:

• encoding: When set to 'base64', module source will be encoded using Base64 algorithm. Setting encoding to false will disable encoding.
• mimetype: A mimetype for data URI. Resolves from module resource extension by default.

webpack.config.js

module.exports = {
  //...
  module: {
    rules: [
      {
        //...
        generator: {
          dataUrl: {
            encoding: 'base64',
            mimetype: 'mimetype/png',
          },
        },
      },
    ],
  },
};

When used a a function, it executes for every module and must return a data URI string.

module.exports = {
  //...
  module: {
    rules: [
      {
        //...
        generator: {
          dataUrl: (content) => {
            const svgToMiniDataURI = require('mini-svg-data-uri');
            if (typeof content !== 'string') {
              content = content.toString();
            }
            return svgToMiniDataURI(content);
          },
        },
      },
    ],
  },
};

Rule.generator.emit

Opt out of writing assets from Asset Modules, you might want to use it in Server side rendering cases.

• Type: boolean = true

• Available: 5.25.0+

• Example:

  module.exports = {
    // …
    module: {
      rules: [
        {
          test: /\.png$/i,
          type: 'asset/resource',
          generator: {
            emit: false,
          },
        },
      ],
    },
  };

Rule.generator.filename

The same as output.assetModuleFilename but for specific rule. Overrides output.assetModuleFilename and works only with asset and asset/resource module types.

webpack.config.js

module.exports = {
  //...
  output: {
    assetModuleFilename: 'images/[hash][ext][query]',
  },
  module: {
    rules: [
      {
        test: /\.png/,
        type: 'asset/resource',
      },
      {
        test: /\.html/,
        type: 'asset/resource',
        generator: {
          filename: 'static/[hash][ext]',
        },
      },
    ],
  },
};

Rule.generator.publicPath

Customize publicPath for specific Asset Modules.

• Type: string | ((pathData: PathData, assetInfo?: AssetInfo) => string)
• Available: 5.28.0+

module.exports = {
  //...
  output: {
    publicPath: 'static/',
  },
  module: {
    rules: [
      {
        test: /\.png$/i,
        type: 'asset/resource',
        generator: {
          publicPath: 'assets/',
        },
      },
    ],
  },
};

Rule.generator.outputPath

Emit the asset in the specified folder relative to 'output.path'. This should only be needed when custom 'publicPath' is specified to match the folder structure there.

• Type: string | ((pathData: PathData, assetInfo?: AssetInfo) => string)
• Available: 5.67.0+

module.exports = {
  //...
  output: {
    publicPath: 'static/',
  },
  module: {
    rules: [
      {
        test: /\.png$/i,
        type: 'asset/resource',
        generator: {
          publicPath: 'https://cdn/assets/',
          outputPath: 'cdn-assets/',
        },
      },
    ],
  },
};

Rule.resource

A Condition matched with the resource. See details in Rule conditions.

Rule.resourceQuery

A Condition matched with the resource query. This option is used to test against the query section of a request string (i.e. from the question mark onwards). If you were to import Foo from './foo.css?inline', the following condition would match:

webpack.config.js

module.exports = {
  //...
  module: {
    rules: [
      {
        test: /\.css$/,
        resourceQuery: /inline/,
        type: 'asset/inline',
      },
    ],
  },
};

Rule.parser.parse

function(input) => string | object

If Rule.type is set to 'json' then Rules.parser.parse option may be a function that implements custom logic to parse module's source and convert it to a JavaScript object. It may be useful to import toml, yaml and other non-JSON files as JSON, without specific loaders:

webpack.config.js

const toml = require('toml');

module.exports = {
  //...
  module: {
    rules: [
      {
        test: /\.toml/,
        type: 'json',
        parser: {
          parse: toml.parse,
        },
      },
    ],
  },
};

Rule.rules

An array of Rules that is also used when the Rule matches.

Rule.scheme

Match the used schema, e.g., data, http.

• Type: string | RegExp | ((value: string) => boolean) | RuleSetLogicalConditions | RuleSetCondition[]
• Available: 5.38.0+

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        scheme: 'data',
        type: 'asset/resource',
      },
    ],
  },
};

Rule.sideEffects

bool

Indicate what parts of the module contain side effects. See Tree Shaking for details.

Rule.test

Include all modules that pass test assertion. If you supply a Rule.test option, you cannot also supply a Rule.resource. See Rule.resource and Condition.test for details.

Rule.type

string

Possible values: 'javascript/auto' | 'javascript/dynamic' | 'javascript/esm' | 'json' | 'webassembly/sync' | 'webassembly/async' | 'asset' | 'asset/source' | 'asset/resource' | 'asset/inline' | 'css/auto'

Rule.type sets the type for a matching module. This prevents defaultRules and their default importing behaviors from occurring. For example, if you want to load a .json file through a custom loader, you'd need to set the type to javascript/auto to bypass webpack's built-in json importing. (See v4.0 changelog for more details)

webpack.config.js

module.exports = {
  //...
  module: {
    rules: [
      //...
      {
        test: /\.json$/,
        type: 'javascript/auto',
        loader: 'custom-json-loader',
      },
    ],
  },
};

See Asset Modules guide for more about asset* type.

css/auto

See use case of css/auto module type here. Make sure to enable experiments.css to use css/auto.

module.exports = {
  target: 'web',
  mode: 'development',
  experiments: {
    css: true,
  },
  module: {
    rules: [
      {
        test: /\.less$/,
        use: 'less-loader',
        type: 'css/auto',
      },
    ],
  },
};

Rule.use

[UseEntry] function(info)

Starting with webpack 5.87.0 falsy values such as undefined null can be used to conditionally disable specific use entry.

[UseEntry]

Rule.use can be an array of UseEntry which are applied to modules. Each entry specifies a loader to be used.

Passing a string (i.e. use: [ 'style-loader' ]) is a shortcut to the loader property (i.e. use: [ { loader: 'style-loader '} ]).

Loaders can be chained by passing multiple loaders, which will be applied from right to left (last to first configured).

webpack.config.js

module.exports = {
  //...
  module: {
    rules: [
      {
        //...
        use: [
          'style-loader',
          {
            loader: 'css-loader',
            options: {
              importLoaders: 1,
            },
          },
          {
            loader: 'less-loader',
            options: {
              noIeCompat: true,
            },
          },
        ],
      },
    ],
  },
};