#Output

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

• Type: Object

#output.assetModuleFilename

• Type: string | ((pathData: PathData, assetInfo?: AssetInfo) => string)
• Default: '[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.

The name of the file to be output by the Asset module. This value can be overridden by Rule.generator.filename.

#output.asyncChunks

• Type: boolean
• Default: true

Create async chunks that are loaded on demand.

#output.charset

• Type: boolean
• Default: false

Add deprecated charset="utf-8" attribute to the HTML <script> tag.

#output.chunkFilename

• Type: string | (pathData: PathData, assetInfo?: AssetInfo) => string
• Default: Determined by output.filename when it is not a function, otherwise '[id].js'.

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 Rspack 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).

export default {
  output: {
    chunkFilename: '[id].js',
  },
};

Usage as a function:

export default {
  output: {
    chunkFilename: pathData => {
      return pathData.chunk.name === 'main' ? '[name].js' : '[name]/[name].js';
    },
  },
};

#output.chunkFormat

• Type: false | 'array-push' | 'commonjs' | 'module' | string
• Default: Determined by target and output.module

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).

export default {
  output: {
    chunkFormat: 'commonjs',
  },
};

#output.chunkLoadTimeout

• Type: number
• Default: 120000

The Number of milliseconds before chunk request timed out.

export default {
  //...
  output: {
    //...
    chunkLoadTimeout: 30000, // 30 seconds before chunk request timed out.
  },
};

#output.chunkLoadingGlobal

• Type: string
• Default: Determined by output.uniqueName

The global variable is used by Rspack for loading chunks.

export default {
  output: {
    chunkLoadingGlobal: 'myCustomFunc',
  },
};

#output.chunkLoading

• Type: false | 'jsonp' | 'import-scripts' | 'require' | 'async-node' | 'import' | 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). The default value will be determined based on the configuration of target and chunkFormat.

export default {
  output: {
    chunkLoading: 'async-node',
  },
};

#output.clean

• Type: boolean | { keep?: string | RegExp | ((path: string) => boolean) }
• Default: false

Before generating the products, delete all files in the output directory.

export default {
  //...
  output: {
    clean: true, // Clean the output directory before emit.
  },

  // or
  output: {
    clean: {
      keep: 'ignored/dir', // keep these assets under 'dist/ignored/dir'.
    },
  },

  // or
  output: {
    clean: {
      keep: /ignored\/dir/, // keep these assets under 'dist/ignored/dir'.
    },
  },

  // or
  output: {
    clean: {
      keep: path => path.includes('ignored/dir'), // keep these assets under 'dist/ignored/dir'.
    },
  },
};

#output.compareBeforeEmit

• Type: boolean
• Default: true

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

export default {
  //...
  output: {
    compareBeforeEmit: false,
  },
};

#output.crossOriginLoading

• Type: false | 'anonymous' | 'use-credentials'
• Default: false

The crossOriginLoading config allows you to set the crossorigin attribute for dynamically loaded chunks.

If target is 'web', Rspack will dynamically create <script> and <link> tags to load asynchronous JavaScript and CSS resources. Rspack will add the crossorigin attribute to the <script> and <link> tags if the URLs of these resources are on other domains and crossOriginLoading is not false.

Optional values

crossOriginLoading has the following optional values:

• false: Do not set the crossorigin attribute.
• 'anonymous': Set crossorigin to 'anonymous' to enable cross-origin without user credentials.
• 'use-credentials': Set crossorigin to 'use-credentials' enable cross-origin with user credentials.

Example

For example, set output.publicPath to https://example.com/ and output.crossOriginLoading to 'anonymous':

import path from 'node:path';

export default {
  output: {
    publicPath: 'https://example.com/',
    crossOriginLoading: 'anonymous',
  },
};

When Rspack dynamically loads JavaScript resources, it will generate the following HTML:

<script src="https://example.com/foo.js" crossorigin="anonymous"></script>

#output.cssChunkFilename

• Type: string | (pathData: PathData, assetInfo?: AssetInfo) => string
• Default: Determined by output.chunkFilename when it is not a function, otherwise '[id].css'.

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

You must not specify an absolute path here. However, feel free to include folders separated by '/'. This specified path combines with the output.path value to pinpoint the location on the disk.

#output.cssFilename

• Type: string | (pathData: PathData, assetInfo?: AssetInfo) => string
• Default: Determined by output.filename

This option determines the name of CSS output files on disk. See output.filename option for details on the possible values.

You must not specify an absolute path here. However, feel free to include folders separated by '/'. This specified path combines with the output.path value to pinpoint the location on the disk.

#output.devtoolFallbackModuleFilenameTemplate

• Type:

type DevtoolFallbackModuleFilenameTemplate =
  | string
  | ((context: ModuleFilenameTemplateContext) => string);

• Default: undefined

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

See output.devtoolModuleFilenameTemplate.

#output.devtoolModuleFilenameTemplate

• Type:

type DevtoolModuleFilenameTemplate =
  | string
  | ((context: ModuleFilenameTemplateContext) => string);

• Default: webpack://[namespace]/[resource-path]?[loaders]'

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'.

export default {
  //...
  output: {
    devtoolModuleFilenameTemplate:
      'webpack://[namespace]/[resource-path]?[loaders]',
  },
};

The following substitutions are available in template strings

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

export default {
  //...
  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

• Type: string
• Default: undefined

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 Rspack.

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

• Type: ('jsonp' | 'import-scripts' | 'require' | 'async-node' | string)[]
• Default: Determined by output.chunkLoading, output.workerChunkLoading and Entry's chunkLoading config.

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

export default {
  //...
  output: {
    enabledChunkLoadingTypes: ['jsonp', 'require'],
  },
};

#output.enabledLibraryTypes

• Type: string[]
• Default: Determined by output.library and Entry

List of library types enabled for use by entry points.

export default {
  //...
  output: {
    enabledLibraryTypes: ['module'],
  },
};

#output.enabledWasmLoadingTypes

• Type: ('fetch-streaming' | 'fetch' | 'async-node' | string | false)[]
• Default: Determined by output.wasmLoading and output.workerWasmLoading

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

export default {
  //...
  output: {
    enabledWasmLoadingTypes: ['fetch'],
  },
};

#output.environment

• Type:

type Environment = {
  /** The environment supports arrow functions ('() => { ... }'). */
  arrowFunction?: boolean;
  /** The environment supports async function and await ('async function () { await ... }'). */
  asyncFunction?: boolean;
  /** The environment supports BigInt as literal (123n). */
  bigIntLiteral?: boolean;
  /** The environment supports const and let for variable declarations. */
  const?: boolean;
  /** The environment supports destructuring ('{ a, b } = obj'). */
  destructuring?: boolean;
  /** The environment supports 'document' variable. */
  document?: boolean;
  /** The environment supports an async import() function to import EcmaScript modules. */
  dynamicImport?: boolean;
  /** The environment supports an async import() when creating a worker, only for web targets at the moment. */
  dynamicImportInWorker?: boolean;
  /** The environment supports 'for of' iteration ('for (const x of array) { ... }'). */
  forOf?: boolean;
  /** The environment supports 'globalThis'. */
  globalThis?: boolean;
  /** The environment supports { fn() {} } */
  methodShorthand?: boolean;
  /** The environment supports ECMAScript Module syntax to import ECMAScript modules (import ... from '...'). */
  module?: boolean;
  /**
   * Determines if the node: prefix is generated for core module imports in environments that support it.
   * This is only applicable to Webpack runtime code.
   * */
  nodePrefixForCoreModules?: boolean;
  /** The environment supports optional chaining ('obj?.a' or 'obj?.()'). */
  optionalChaining?: boolean;
  /** The environment supports template literals. */
  templateLiteral?: boolean;
};

output.environment specifies which ECMAScript language features and host environment capabilities Rspack is allowed to use when generating its runtime code.

This setting affects only code emitted by Rspack itself, such as runtime helpers. It does not downgrade your application source code.

#Default behavior

By default, output.environment is automatically inferred from your target configuration.

Rspack evaluates target to determine which features your target environment supports. For example:

• If the target browsers support arrow functions, Rspack will use arrow functions in the runtime to produce more compact output.
• If target specifies a particular Node.js version, Rspack will infer the supported syntax from that version’s capabilities.

In general, you do not need to configure this option manually. You would override it only when you want to explicitly enforce or restrict specific features. Manual configuration replaces the inferred values and gives you direct control over the syntax used in the generated runtime.

#Example

Suppose target is set to ['web', 'es2018']. In this case, Rspack will infer that const is supported and enable it by default. You can disable it by setting output.environment.const: false. Rspack will then emit runtime code that uses var declarations instead.

export default {
  target: ['web', 'es2018'],
  output: {
    environment: {
      const: false,
    },
  },
};

#output.filename

• Type: string | (pathData: PathData, assetInfo?: AssetInfo) => string
• Default: When output.module is true, it is '[name].mjs', otherwise it is '[name].js'.

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.

export default {
  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...

Use Entry name:

export default {
  //...
  output: {
    filename: '[name].bundle.js',
  },
};

Using internal chunk id:

export default {
  //...
  output: {
    filename: '[id].bundle.js',
  },
};

Using hashes generated from the generated content:

export default {
  //...
  output: {
    filename: '[contenthash].bundle.js',
  },
};

Combining multiple substitutions:

export default {
  //...
  output: {
    filename: '[name].[contenthash].bundle.js',
  },
};

Using the function to return the filename:

export default {
  //...
  output: {
    filename: pathData => {
      return pathData.chunk.name === 'main' ? '[name].js' : '[name]/[name].js';
    },
  },
};

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.

#output.globalObject

• Type: string
• Default: 'self'

When targeting a library, especially when library.type 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 type option, the global object could change respectively, e.g., self, global, or globalThis.

For example:

export default {
  // ...
  output: {
    library: 'myLib',
    libraryTarget: 'umd',
    filename: 'myLib.js',
    globalObject: 'this',
  },
};

#output.hashDigest

• Type: string
• Default: 'hex'

The encoding to use when generating the hash. Using 'base64' for filenames might be problematic since it has the character / in its alphabet. Likewise 'latin1' could contain any character.

#output.hashDigestLength

• Type: number
• Default: 16

The prefix length of the hash digest to use, see Hash length for more details.

export default {
  output: {
    hashDigestLength: 8,
  },
};

#output.hashFunction

• Type: 'md4' | 'xxhash64' | 'sha256'
• Default: 'xxhash64'

The hashing algorithm to use.

export default {
  output: {
    hashFunction: 'xxhash64',
  },
};

#output.hashSalt

• Type: string
• Default: undefined

An optional salt to update the hash.

#output.hotUpdateChunkFilename

• Type: string
• Default: "[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:

export default {
  output: {
    hotUpdateChunkFilename: '[id].[fullhash].hot-update.js',
  },
};

#output.hotUpdateGlobal

• Type: string
• Default: "webpackHotUpdate" + output.uniqueName

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

• Type: string
• Default: "[runtime].[fullhash].hot-update.json"

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

#output.iife

• Type: boolean
• Default: true

Tells Rspack to add IIFE wrapper around emitted code.

export default {
  output: {
    iife: true,
  },
};

#output.importFunctionName

• Type: string
• Default: 'import'

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

export default {
  //...
  output: {
    importFunctionName: '__import__',
  },
};

#output.importMetaName

• Type: string
• Default: 'import.meta'

The name of the native import.meta object (can be exchanged for a polyfill).

export default {
  //...
  output: {
    importMetaName: 'pseudoImport.meta',
  },
};

#output.library

Output a library exposing the exports of your entry point.

• Type: string | string[] | object

Let's take a look at an example.

export default {
  // …
  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 Rspack bundled library:

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

In the above example, we're passing a single entry file to entry, however, Rspack 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.

   rspack.config.mjs

   export default {
     // …
     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:

   rspack.config.mjs

   export default {
     // …
     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('rspack');
     MyLibrary.b.hello('rspack');
   </script>

#output.library.amdContainer

• Type: string

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

export default {
  // …
  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

Specify a name for the library.

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

export default {
  // …
  output: {
    library: {
      name: 'MyLibrary',
    },
  },
};

#output.library.type

Configure how the library will be exposed.

• Type: string

  Types included by default are 'var', 'module', 'system', 'assign', 'assign-properties', 'this', 'window', 'self', 'global', 'commonjs', 'commonjs2', 'commonjs-module', 'commonjs-static', 'amd', 'amd-require', 'umd', 'umd2', 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'

export default {
  // …
  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'

export default {
  // …
  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'

export default {
  // …
  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'

export default {
  // …
  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'

export default {
  // …
  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'

export default {
  // …
  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'

export default {
  // …
  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'

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

Output ES modules.

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: 'modern-module'

export default {
  // …
  experiments: {
    outputModule: true,
  },
  output: {
    library: {
      // do not specify a `name` here
      type: 'modern-module',
    },
  },
};

This configuration generates tree-shakable output for ES Modules.

However this feature is still experimental and not fully supported yet, so make sure to enable experiments.outputModule beforehand.

#type: 'commonjs2'

export default {
  // …
  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'

export default {
  // …
  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:

export default {
  //...
  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'

export default {
  //...
  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 Rspack 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:

export default {
  //...
  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:

export default {
  //...
  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:

export default {
  //...
  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.

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

export default {
  //...
  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'

export default {
  // …
  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[]
• Default: undefined

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'.

export default {
  output: {
    library: {
      name: 'MyLibrary',
      type: 'var',
      export: 'default',
    },
  },
};

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

// If your library 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:

export default {
  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 }
• Default: undefined

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

export default {
  // …
  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:

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

#output.library.umdNamedDefine

• Type: boolean
• Default: undefined

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.

export default {
  //...
  output: {
    library: {
      name: 'MyLibrary',
      type: 'umd',
      umdNamedDefine: true,
    },
  },
};

The AMD module will be:

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

#output.module

• Type: boolean
• Default: false

Output JavaScript files as module type. Disabled by default as it's an experimental feature. To use it, you must set experiments.outputModule to true.

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

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

export default {
  //...
  experiments: {
    outputModule: true,
  },
  output: {
    module: true,
  },
};

#output.path

• Type: string
• Default: path.resolve(process.cwd(), 'dist')

The output directory as an absolute path.

import path from 'node:path';
import { fileURLToPath } from 'node:url';

const __dirname = path.dirname(fileURLToPath(import.meta.url));

export default {
  output: {
    path: path.resolve(__dirname, 'dist/assets'),
  },
};

const path = require('node: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.

#output.pathinfo

• Type: boolean | 'verbose'
• Default: false

Controls whether Rspack adds module-related comments to the generated bundle. These comments are useful for debugging, inspecting build output, and understanding tree-shaking behavior.

• true: Enables basic comments, including module path information.
• false: Disables all comments, which is the default behavior.
• 'verbose': Outputs detailed comments, such as module exports, runtime details, tree-shaking information, and bailout reasons. This mode is helpful when diagnosing build issues or performing in-depth bundle analysis.

For example, enabling pathinfo:

export default {
  output: {
    pathinfo: true,
  },
};

The generated bundle will contain comments like:

/*!**********************!*\
  !*** ./src/index.js ***!
  \**********************/

#output.publicPath

• Type: 'auto' | string | ((pathData: PathData, assetInfo?: AssetInfo) => string)
• Default: 'auto' when target is 'web' or 'webworker', undefined otherwise

Set the base URL path prefix for bundled static assets (such as JS, CSS, images, etc.).

export default {
  output: {
    publicPath: '/assets/',
  },
};

See Asset base path for more details.

#output.scriptType

• Type: 'module' | 'text/javascript' | boolean
• Default: false

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

export default {
  //...
  output: {
    scriptType: 'module',
  },
};

#output.sourceMapFilename

• Type: string
• Default: '[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 Filename placeholders.

#output.strictModuleErrorHandling

• Type: boolean
• Default: false

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

export default {
  //...
  output: {
    strictModuleErrorHandling: true,
  },
};

#output.strictModuleExceptionHandling

• Types: boolean

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

#output.trustedTypes

• Type: true | string | object
• Default: undefined

Controls Trusted Types compatibility. When enabled, Rspack 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 is disabled by default (no compatibility, script URLs are strings).

• When set to true, Rspack 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.

export default {
  //...
  output: {
    trustedTypes: {
      policyName: 'my-application#webpack',
    },
  },
};

#output.trustedTypes.onPolicyCreationFailure

• Type: "stop" | "continue"
• Default: "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.

export default {
  //...
  output: {
    //...
    trustedTypes: {
      policyName: 'my-application#webpack',
      onPolicyCreationFailure: 'continue',
    },
  },
};

#output.uniqueName

• Type: string
• Default: 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 ''.

A unique name of the Rspack build to avoid multiple Rspack runtimes to conflict when using globals.

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

• output.chunkLoadingGlobal

export default {
  output: {
    uniqueName: 'my-package-xyz',
  },
};

#output.wasmLoading

• Type: false | 'fetch', 'async-node'
• Default: 'fetch'

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'.

export default {
  //...
  output: {
    wasmLoading: 'fetch',
  },
};

#output.webassemblyModuleFilename

• Type: string
• Default: '[hash].module.wasm'

Specifies the filename of WebAssembly modules. It should be provided as a relative path within the output.path directory

export default {
  //...
  output: {
    webassemblyModuleFilename: '[contenthash:8].wasm',
  },
};

#output.workerChunkLoading

• Type: false | 'jsonp' | 'import-scripts' | 'require' | 'async-node' | 'import'
• Default: false

The new option workerChunkLoading controls the chunk loading of workers.

export default {
  //...
  output: {
    workerChunkLoading: false,
  },
};

#output.workerPublicPath

• Type: string
• Default: ""

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.

export default {
  //...
  output: {
    workerPublicPath: '/workerPublicPath2/',
  },
};

#output.workerWasmLoading

• Type: false | 'fetch-streaming' | 'fetch' | 'async-node' | string
• Default: false

Option to set the method of loading WebAssembly Modules in workers, defaults to the value of output.wasmLoading.

export default {
  //...
  output: {
    workerWasmLoading: 'fetch',
  },
};

#output.auxiliaryComment

#output.libraryExport

#output.libraryTarget

#output.umdNamedDefine

#output.cssHeadDataCompression

• Type: boolean
• Default: false for development mode, true for production mode

Rspack adds some metadata in CSS to parse CSS modules, and this configuration determines whether to compress these metadata.

For example

.local-a {
  color: blue;
}

head {
  --webpack-main: a: local-a/&\.\/ src\/index\.module\.css;
}

After compress 👇

.local-a {
  color: blue;
}

head {
  --webpack-main: &\.\/ srcăindexāmoduleācss;
}