# Source: https://rspack.dev/config/externals.md

CC 4.0 License> The content of this section is derived from the content of the following links and is subject to the CC BY 4.0 license.
> 
> - [https://webpack.js.org/configuration/externals/](https://webpack.js.org/configuration/externals/)
> 
> The following contents can be assumed to be the result of modifications and deletions based on the original contents if not specifically stated.
> 
> 


# Externals

The `externals` configuration option provides a way of excluding dependencies from the output bundles. Instead, the created bundle relies on that dependency to be present in the consumer's (any end-user application) environment. This feature is typically most useful to **library developers**, however there are a variety of applications for it.

## externals

- **Type:** `string | object | function | RegExp | Array<string | object | function | RegExp>`

**Prevent bundling** of certain `import`ed packages and instead retrieve these _external dependencies_ at runtime.

For example, to include [jQuery](https://jquery.com/) from a CDN instead of bundling it:

```html title="index.html"
<script
  src="https://code.jquery.com/jquery-3.1.0.js"
  integrity="sha256-slogkvB1K3VOkzAI8QITxV3VzpOnkeNVsKvtkYLMjfk="
  crossorigin="anonymous"
></script>
```

```js title="rspack.config.mjs"
export default {
  //...
  externals: {
    jquery: 'jquery',
  },
};
```

This leaves any dependent modules unchanged, i.e. the code shown below will still work:

```js
import $ from 'jquery';

$('.my-element').animate(/* ... */);
```

The property name `jquery` specified under `externals` in the above Rspack configuration indicates that the module `jquery` in `import $ from 'jquery'` should be excluded from bundling. In order to replace this module, the value `jQuery` will be used to retrieve a global `jQuery` variable, as the default external library type is `var`, see [externalsType](#externalstype).

While we showed an example consuming external global variable above, the external can actually be available in any of these forms: global variable, CommonJS, AMD, ES2015 Module, see more in [externalsType](#externalstype).

### string

Depending on the [externalsType](#externalstype), this could be the name of the global variable (see [`'global'`](#externalstypeglobal), [`'this'`](#externalstypethis), [`'var'`](#externalstypevar), [`'window'`](#externalstypewindow)) or the name of the module (see `amd`, [`commonjs`](#externalstypecommonjs), [`module`](#externalstypemodule), `umd`).

You can also use the shortcut syntax if you're defining only 1 external:

```js title="rspack.config.mjs"
export default {
  //...
  externals: 'jquery',
};
```

equals to

```js title="rspack.config.mjs"
export default {
  //...
  externals: {
    jquery: 'jquery',
  },
};
```

You can specify the [external library type](#externalstype) to the external with the `${externalsType} ${libraryName}` syntax. It will override the default external library type specified in the [externalsType](#externalstype) option.

For example, if the external library is a [CommonJS module](#externalstypecommonjs), you can specify

```js title="rspack.config.mjs"
export default {
  //...
  externals: {
    jquery: 'commonjs jquery',
  },
};
```

### string\[]\{#string-array}

```js title="rspack.config.mjs"
export default {
  //...
  externals: {
    subtract: ['./math', 'subtract'],
  },
};
```

`subtract: ['./math', 'subtract']` allows you select part of a module, where `./math` is the module and your bundle only requires the subset under the `subtract` variable.

When the `externalsType` is `commonjs`, this example would translate to `require('./math').subtract;` while when the `externalsType` is `window`, this example would translate to `window["./math"]["subtract"];`

Similar to the [string syntax](#string), you can specify the external library type with the `${externalsType} ${libraryName}` syntax, in the first item of the array, for example:

```js title="rspack.config.mjs"
export default {
  //...
  externals: {
    subtract: ['commonjs ./math', 'subtract'],
  },
};
```

### object

:::warning
An object with `{ root, commonjs, commonjs2, amd, ... }` is only allowed for [`library.type: 'umd'`](/config/output.md#outputlibrarytarget) and [`externalsType: 'umd'`](#externalstype). It's not allowed for other library targets.
:::

```js title="rspack.config.mjs"
export default {
  externals: {
    // When `library.type: 'umd'` and `externalsType: 'umd'`, the following format must be strictly followed:
    lodash: {
      root: '_', // indicates global variable
      commonjs: 'lodash',
      commonjs2: 'lodash',
      amd: 'lodash',
    },
  },
};
```

This syntax is used to describe all the possible ways that an external library can be made available. `lodash` here is available as `lodash` under AMD and CommonJS module systems but available as `_` in a global variable form. `subtract` here is available via the property `subtract` under the global `math` object (e.g. `window['math']['subtract']`).

### function

- **Type:**
  - `function ({ context, request, contextInfo, getResolve }, callback)`
  - `function ({ context, request, contextInfo, getResolve }) => promise`

It might be useful to define your own function to control the behavior of what you want to externalize from Rspack. [webpack-node-externals](https://www.npmjs.com/package/webpack-node-externals), for example, excludes all modules from the `node_modules` directory and provides options to allowlist packages.

Here're arguments the function can receive:

- `ctx` (`object`): Object containing details of the file.
  - `ctx.context` (`string`): The directory of the file which contains the import.
  - `ctx.request` (`string`): The import path being requested.
  - `ctx.contextInfo` (`object`): Contains information about the issuer (e.g. the layer and compiler)
  - `ctx.getResolve`: Get a resolve function with the current resolver options.
- `callback` (`function (err, result, type)`): Callback function used to indicate how the module should be externalized.

The callback function takes three arguments:

- `err` (`Error`): Used to indicate if there has been an error while externalizing the import. If there is an error, this should be the only parameter used.
- `result` (`string | string[] | object | boolean`): Describes the external module.
  - `string | string[] | object`: Describes the external module with the other external formats ([`string`](#string), [`string[]`](#string-array), or [`object`](#object)).
  - `boolean`: Passing `true` externalizes the dependency using the original request path as the external module name. Passing `false` tells Rspack to skip the remaining external configuration and bundle the dependency instead.
- `type` (`string`): Optional parameter that indicates the module [external type](#externalstype) (if it has not already been indicated in the `result` parameter).

As an example, to externalize all imports where the import path matches a regular expression you could do the following:

```js title="rspack.config.mjs"
export default {
  //...
  externals: [
    function ({ context, request }, callback) {
      if (/^yourregex$/.test(request)) {
        // Externalize to a commonjs module using the request path
        return callback(null, 'commonjs ' + request);
      }

      // Continue without externalizing the import
      callback();
    },
  ],
};
```

Other examples using different module formats:

```js title="rspack.config.mjs"
export default {
  externals: [
    function (ctx, callback) {
      // The external is a `commonjs2` module located in `@scope/library`
      callback(null, '@scope/library', 'commonjs2');
    },
  ],
};
```

```js title="rspack.config.mjs"
export default {
  externals: [
    function (ctx, callback) {
      // The external is a global variable called `nameOfGlobal`.
      callback(null, 'nameOfGlobal');
    },
  ],
};
```

```js title="rspack.config.mjs"
export default {
  externals: [
    function (ctx, callback) {
      // The external is a named export in the `@scope/library` module.
      callback(null, ['@scope/library', 'namedexport'], 'commonjs');
    },
  ],
};
```

```js title="rspack.config.mjs"
export default {
  externals: [
    function (ctx, callback) {
      // The external is a UMD module
      callback(null, {
        root: 'componentsGlobal',
        commonjs: '@scope/components',
        commonjs2: '@scope/components',
        amd: 'components',
      });
    },
  ],
};
```

### RegExp

Every dependency that matches the given regular expression will be excluded from the output bundles.

```js title="rspack.config.mjs"
export default {
  //...
  externals: /^(jquery|\$)$/i,
};
```

In this case, any dependency named `jQuery`, capitalized or not, or `$` would be externalized.

### Combining syntaxes

Sometimes you may want to use a combination of the above syntaxes. This can be done in the following manner:

```js title="rspack.config.mjs"
export default {
  //...
  externals: [
    {
      // String
      react: 'react',
      // Object
      lodash: {
        commonjs: 'lodash',
        amd: 'lodash',
        root: '_', // indicates global variable
      },
      // [string]
      subtract: ['./math', 'subtract'],
    },
    // Function
    function ({ context, request }, callback) {
      if (/^yourregex$/.test(request)) {
        return callback(null, 'commonjs ' + request);
      }
      callback();
    },
    // Regex
    /^(jquery|\$)$/i,
  ],
};
```

:::warning
[Default type](#externalstype) will be used if you specify `externals` without a type e.g. `externals: { react: 'react' }` instead of `externals: { react: 'commonjs-module react' }`.
:::

## externalsType

- **Type:** `string`
- **Default:** `'var'`

Specify the default type of externals. `amd`, `umd`, `system` and `jsonp` externals **depend on the [`output.library.type`](/config/output.md#outputlibrarytype)** being set to the same value e.g. you can only consume `amd` externals within an `amd` library.

Supported types:

- `'amd'`
- `'amd-require'`
- `'assign'` - same as `'var'`
- [`'commonjs'`](#externalstypecommonjs)
- `'commonjs-module'`
- [`'global'`](#externalstypeglobal)
- [`'module'`](#externalstypemodule)
- [`'import'`](#externalstypeimport) - uses `import()` to load a native ECMAScript module (async module)
- [`'module-import'`](#externalstypemodule-import)
- [`'commonjs-import'`](#externalstypecommonjs-import)
- `'jsonp'`
- [`'node-commonjs'`](#externalstypenode-commonjs)
- [`'promise'`](#externalstypepromise) - same as `'var'` but awaits the result (async module)
- [`'self'`](#externalstypeself)
- `'system'`
- [`'script'`](#externalstypescript)
- [`'this'`](#externalstypethis)
- `'umd'`
- `'umd2'`
- [`'var'`](#externalstypevar)
- [`'window'`](#externalstypewindow)

```js title="rspack.config.mjs"
export default {
  //...
  externalsType: 'promise',
};
```

### externalsType.commonjs

Specify the default type of externals as `'commonjs'`. Rspack will generate code like `const X = require('...')` for externals used in a module.

**Example**

```js
import fs from 'fs-extra';
```

```js title="rspack.config.mjs"
export default {
  externalsType: 'commonjs',
  externals: {
    'fs-extra': 'fs-extra',
  },
};
```

Will generate into something like:

```js
const fs = require('fs-extra');
```

Note that there will be a `require()` in the output bundle.

### externalsType.global

Specify the default type of externals as `'global'`. Rspack will read the external as a global variable on the [`globalObject`](/config/output.md#outputglobalobject).

**Example**

```js
import jq from 'jquery';
jq('.my-element').animate(/* ... */);
```

```js title="rspack.config.mjs"
export default {
  externalsType: 'global',
  externals: {
    jquery: '$',
  },
  output: {
    globalObject: 'global',
  },
};
```

Will generate into something like

```js
const jq = global['$'];
jq('.my-element').animate(/* ... */);
```

### externalsType.module

Specify the default type of externals as `'module'`. Rspack will generate code like `import * as X from '...'` for externals used in a module.

Make sure to enable [`experiments.outputModule`](/config/experiments.md#experimentsoutputmodule) first, otherwise Rspack will throw errors.

**Example**

```js
import jq from 'jquery';
jq('.my-element').animate(/* ... */);
```

```js title="rspack.config.mjs"
export default {
  experiments: {
    outputModule: true,
  },
  externalsType: 'module',
  externals: {
    jquery: 'jquery',
  },
};
```

Will generate into something like

```js
import * as __rspack_external_jquery from 'jquery';

const jq = __rspack_external_jquery['default'];
jq('.my-element').animate(/* ... */);
```

Note that there will be an `import` statement in the output bundle.

### externalsType.import

Specify the default type of externals as `'import'`. Rspack will generate code like `import('...')` for externals used in a module.

**Example**

```js
async function foo() {
  const jq = await import('jquery');
  jq('.my-element').animate(/* ... */);
}
```

```js title="rspack.config.mjs"
export default {
  externalsType: 'import',
  externals: {
    jquery: 'jquery',
  },
};
```

Will generate into something like

```js
var __webpack_modules__ = {
  jquery: (module) => {
    module.exports = import('jquery');
  },
};

// webpack runtime...

async function foo() {
  const jq = await Promise.resolve(/* import() */).then(
    __webpack_require__.bind(__webpack_require__, 'jquery'),
  );
  jq('.my-element').animate(/* ... */);
}
```

Note that there will be an `import()` statement in the output bundle.

### externalsType\['module-import']

Specify the default type of externals as `'module-import'`. This combines [`'module'`](#externalstypemodule) and [`'import'`](#externalstypeimport). Rspack will automatically detect the type of import syntax, setting it to `'module'` for static imports and `'import'` for dynamic imports.

Make sure to enable [`experiments.outputModule`](/config/index.md#experimentsoutputmodule) first if static imports exist, otherwise Rspack will throw errors.

**Example**

```js
import { attempt } from 'lodash';

async function foo() {
  const jq = await import('jquery');
  attempt(() => jq('.my-element').animate(/* ... */));
}
```

```js title="rspack.config.mjs"
export default {
  externalsType: 'module-import',
  externals: {
    lodash: 'lodash',
    jquery: 'jquery',
  },
};
```

Will generate into something like

```js
import * as __rspack_external_lodash from 'lodash';
const lodash = __rspack_external_jquery;

var __webpack_modules__ = {
  jquery: (module) => {
    module.exports = import('jquery');
  },
};

// webpack runtime...

async function foo() {
  const jq = await Promise.resolve(/* import() */).then(
    __webpack_require__.bind(__webpack_require__, 'jquery'),
  );
  (0, lodash.attempt)(() => jq('.my-element').animate(/* ... */));
}
```

Note that there will be an `import` or `import()` statement in the output bundle.

When a module is not imported via `import` or `import()`, Rspack will use `"module"` externals type as fallback. If you want to use a different type of externals as fallback, you can specify it with a function in the `externals` option. For example:

```js title="rspack.config.mjs"
export default {
  externalsType: "module-import",
  externals: [
    function (
      { request, dependencyType },
      callback
    ) {
      if (dependencyType === "commonjs") {
        return callback(null, `node-commonjs ${request}`);
      }
      callback();
    },
  ]
```

### externalsType\['commonjs-import']

Specify the default type of externals as `'commonjs-import'`. This combines [`'commonjs'`](#externalstypecommonjs) and [`'import'`](#externalstypeimport). Rspack will automatically detect the type of import syntax, setting dynamic import to `'import'` and leaving others to `'commonjs'`.

This is useful when building a Node.js application that target Node.js version higher than `13.2.0`, which supports both [`import()` expressions](https://nodejs.org/api/esm.html#import-expressions) and `require()`.

:::note
`commonjs-import` type is only available of Rspack, and not applicable for webpack.
:::

**Example**

```js
import { attempt } from 'lodash';

async function foo() {
  const jq = await import('jquery');
  attempt(() => jq('.my-element').animate(/* ... */));
}
```

```js title="rspack.config.mjs"
export default {
  externalsType: 'commonjs-import',
  externals: {
    lodash: 'lodash',
    jquery: 'jquery',
  },
};
```

Will generate into something like

```js
var __webpack_modules__ = {
  lodash: function (module) {
    module.exports = require('lodash');
  },
  jquery: function (module) {
    module.exports = import('jquery');
  },
};

// Rspack runtime...

async function foo() {
  const jq = await Promise.resolve(/* import() */).then(
    __webpack_require__.bind(__webpack_require__, 'jquery'),
  );
  (0, lodash__rspack_import_0__.attempt)(() =>
    jq('.my-element').animate(/* ... */),
  );
}
```

Note that there will be an `import()` statement in the output bundle.

### externalsType\['node-commonjs']

Specify the default type of externals as `'node-commonjs'`. Rspack will import [`createRequire`](https://nodejs.org/api/module.html#module_module_createrequire_filename) from `'module'` to construct a require function for loading externals used in a module.

**Example**

```js
import jq from 'jquery';
jq('.my-element').animate(/* ... */);
```

```js title="rspack.config.mjs"
export default {
  experiments: {
    outputModule: true,
  },
  externalsType: 'node-commonjs',
  externals: {
    jquery: 'jquery',
  },
};
```

Will generate into something like

```js
import { createRequire } from 'module';

const jq = createRequire(import.meta.url)('jquery');
jq('.my-element').animate(/* ... */);
```

Note that there will be an `import` statement in the output bundle.

### externalsType.promise

Specify the default type of externals as `'promise'`. Rspack will read the external as a global variable (similar to [`'var'`](#externalstypepromise)) and `await` for it.

**Example**

```js
import jq from 'jquery';
jq('.my-element').animate(/* ... */);
```

```js title="rspack.config.mjs"
export default {
  externalsType: 'promise',
  externals: {
    jquery: '$',
  },
};
```

Will generate into something like

```js
const jq = await $;
jq('.my-element').animate(/* ... */);
```

### externalsType.self

Specify the default type of externals as `'self'`. Rspack will read the external as a global variable on the `self` object.

**Example**

```js
import jq from 'jquery';
jq('.my-element').animate(/* ... */);
```

```js title="rspack.config.mjs"
export default {
  externalsType: 'self',
  externals: {
    jquery: '$',
  },
};
```

Will generate into something like

```js
const jq = self['$'];
jq('.my-element').animate(/* ... */);
```

### externalsType.script

Specify the default type of externals as `'script'`. Rspack will load the external as a script exposing predefined global variables with HTML `<script>` element. The `<script>` tag would be removed after the script has been loaded.

**Syntax**

```js title="rspack.config.mjs"
export default {
  externalsType: 'script',
  externals: {
    packageName: [
      'http://example.com/script.js',
      'global',
      'property',
      'property',
    ], // properties are optional
  },
};
```

You can also use the shortcut syntax if you're not going to specify any properties:

```js title="rspack.config.mjs"
export default {
  externalsType: 'script',
  externals: {
    packageName: 'global@http://example.com/script.js', // no properties here
  },
};
```

Note that [`output.publicPath`](/config/output.md#outputpublicpath) won't be added to the provided URL.

**Example**

Let's load a `lodash` from CDN:

```js title="rspack.config.mjs"
export default {
  externalsType: 'script',
  externals: {
    lodash: ['https://cdn.jsdelivr.net/npm/lodash@4.17.19/lodash.min.js', '_'],
  },
};
```

Then use it in code:

```js
import _ from 'lodash';
console.log(_.head([1, 2, 3]));
```

Here's how we specify properties for the above example:

```js title="rspack.config.mjs"
export default {
  externalsType: 'script',
  externals: {
    lodash: [
      'https://cdn.jsdelivr.net/npm/lodash@4.17.19/lodash.min.js',
      '_',
      'head',
    ],
  },
};
```

Both local variable `head` and global `window._` will be exposed when you `import` `lodash`:

```js
import head from 'lodash';
console.log(head([1, 2, 3])); // logs 1 here
console.log(window._.head(['a', 'b'])); // logs a here
```

:::tip
When loading code with HTML `<script>` tags, the Rspack runtime will try to find an existing `<script>` tag that matches the `src` attribute or has a specific `data-rspack` attribute. For chunk loading `data-rspack` attribute would have value of `'[output.uniqueName]:chunk-[chunkId]'` while external script has value of `'[output.uniqueName]:[global]'`.

Options like `output.chunkLoadTimeout`, `output.crossOriginLoading` and `output.scriptType` will also have effect on the external scripts loaded this way.
:::

### externalsType.this

Specify the default type of externals as `'this'`. Rspack will read the external as a global variable on the `this` object.

**Example**

```js
import jq from 'jquery';
jq('.my-element').animate(/* ... */);
```

```js title="rspack.config.mjs"
export default {
  externalsType: 'this',
  externals: {
    jquery: '$',
  },
};
```

Will generate into something like

```js
const jq = this['$'];
jq('.my-element').animate(/* ... */);
```

### externalsType.var

Specify the default type of externals as `'var'`. Rspack will read the external as a global variable.

**Example**

```js
import jq from 'jquery';
jq('.my-element').animate(/* ... */);
```

```js title="rspack.config.mjs"
export default {
  externalsType: 'var',
  externals: {
    jquery: '$',
  },
};
```

Will generate into something like

```js
const jq = $;
jq('.my-element').animate(/* ... */);
```

### externalsType.window

Specify the default type of externals as `'window'`. Rspack will read the external as a global variable on the `window` object.

**Example**

```js
import jq from 'jquery';
jq('.my-element').animate(/* ... */);
```

```js title="rspack.config.mjs"
export default {
  externalsType: 'window',
  externals: {
    jquery: '$',
  },
};
```

Will generate into something like

```js
const jq = window['$'];
jq('.my-element').animate(/* ... */);
```

## externalsPresets

- **Type:** `object`

Enable presets of externals for specific targets.

### externalsPresets.electron

**Type:** `boolean`

Treat common electron built-in modules in main and preload context like `electron`, `ipc` or `shell` as external and load them via `require()` when used.

### externalsPresets.electronMain

**Type:** `boolean`

Treat electron built-in modules in the main context like `app`, `ipc-main` or `shell` as external and load them via `require()` when used.

### externalsPresets.electronPreload

**Type:** `boolean`

Treat electron built-in modules in the preload context like `web-frame`, `ipc-renderer` or `shell` as external and load them via require() when used.

### externalsPresets.electronRenderer

**Type:** `boolean`

Treat electron built-in modules in the renderer context like `web-frame`, `ipc-renderer` or `shell` as external and load them via `require()` when used.

### externalsPresets.node

**Type:** `boolean`

Treat node.js built-in modules like `fs`, `path` or `vm` as external and load them via `require()` when used.

### externalsPresets.nwjs

**Type:** `boolean`

Treat `NW.js` legacy `nw.gui` module as external and load it via `require()` when used.

### externalsPresets.web

**Type:** `boolean`

Treat references to `http(s)://...` and `std:...` as external and load them via `import` when used. **(Note that this changes execution order as externals are executed before any other code in the chunk)**.

### externalsPresets.webAsync

**Type:** `boolean`

Treat references to `http(s)://...` and `std:...` as external and load them via `async import()` when used **(Note that this external type is an `async` module, which has various effects on the execution)**.

Note that if you're going to output ES modules with those node.js-related presets, Rspack will set the default `externalsType` to [`node-commonjs`](#externalstypenode-commonjs) which would use `createRequire` to construct a require function instead of using `require()`.

**Example**

Using `node` preset will not bundle built-in modules and treats them as external and loads them via `require()` when used.

```js title="rspack.config.mjs"
export default {
  externalsPresets: {
    node: true,
  },
};
```