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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`

string [string] object function RegExp

Prevent bundling of certain imported packages and instead retrieve these external dependencies at runtime.

For example, to include jQuery from a CDN instead of bundling it:

index.html

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

webpack.config.js

module.exports = {
  //...
  externals: {
    jquery: 'jQuery'
  }
};

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

import $ from 'jquery';

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

The bundle with external dependencies can be used in various module contexts, such as CommonJS, AMD, global and ES2015 modules. The external library may be available in any of these forms:

root: The library should be available as a global variable (e.g. via a script tag).
commonjs: The library should be available as a CommonJS module.
commonjs2: Similar to the above but where the export is module.exports.default.
amd: Similar to commonjs but using AMD module system.

The following syntaxes are accepted...

string

See the example above. The property name jquery indicates that the module jquery in import $ from 'jquery' should be excluded. In order to replace this module, the value jQuery will be used to retrieve a global jQuery variable. In other words, when a string is provided it will be treated as root (defined above and below).

On the other hand, if you want to externalise a library that is available as a CommonJS module, you can provide the external library type together with the library name.

For example, if you want to exclude fs-extra from the output bundle and import it during the runtime instead, you can specify it as follows:

module.exports = {
  // ...
  externals: {
    'fs-extra': 'commonjs2 fs-extra',
  }
};

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

import fs from 'fs-extra';

will compile to something like:

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

[string]

module.exports = {
  //...
  externals: {
    subtract: ['./math', 'subtract']
  }
};

subtract: ['./math', 'subtract'] allows you select part of a commonjs module, where ./math is the module and your bundle only requires the subset under the subtract variable. This example would translate to require('./math').subtract;

object

An object with { root, amd, commonjs, ... } is only allowed for libraryTarget: 'umd'. It's not allowed for other library targets.

module.exports = {
  //...
  externals : {
    react: 'react'
  },

  // or

  externals : {
    lodash : {
      commonjs: 'lodash',
      amd: 'lodash',
      root: '_' // indicates global variable
    }
  },

  // or

  externals : {
    subtract : {
      root: ['math', 'subtract']
    }
  }
};

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

function (context, request, callback)

It might be useful to define your own function to control the behavior of what you want to externalize from webpack. webpack-node-externals, for example, excludes all modules from the node_modules directory and provides options to whitelist packages.

The function receives three arguments:

context (string): The directory of the file which contains the import.
request (string): The import path being requested.
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): Describes the external module. Can accept a string in the format ${type} ${path}, or one of the other standard external formats (string, [string], or object)
type (string): Optional parameter that indicates the module type (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:

webpack.config.js

module.exports = {
  //...
  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:

webpack.config.js

module.exports = {
  externals: [
    function(context, request, callback) {
      // The external is a `commonjs2` module located in `@scope/library`
      callback(null, '@scope/library', 'commonjs2');
    }
  ]
};

webpack.config.js

module.exports = {
  externals: [
    function(context, request, callback) {
      // The external is a global variable called `nameOfGlobal`.
      callback(null, 'nameOfGlobal');
    }
  ]
};

webpack.config.js

module.exports = {
  externals: [
    function(context, request, callback) {
      // The external is a named export in the `@scope/library` module.
      callback(null, ['@scope/library', 'namedexport'], 'commonjs');
    }
  ]
};

webpack.config.js

module.exports = {
  externals: [
    function(context, request, 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.

webpack.config.js

module.exports = {
  //...
  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:

webpack.config.js

module.exports = {
  //...
  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
  ]
};

Default type will be used if you specify externals without a type e.g. externals: { react: 'react' } instead of externals: { react: 'commonjs-module react' }.

For more information on how to use this configuration, please refer to the article on how to author a library.

`externalsType`

string = 'var'

Specifies the default type of externals. amd, umd, system and jsonp externals depend on the output.libraryTarget being set to the same value e.g. you can only consume amd externals within an amd library.

Supported types:

'var'
'module'
'assign'
'this'
'window'
'self'
'global'
'commonjs'
'commonjs-module'
'amd'
'amd-require'
'umd'
'umd2'
'jsonp'
'system'
'promise' - same as 'var' but awaits the result (async module)
'import' - uses import() to load a native EcmaScript module (async module)

webpack.config.js

module.exports = {
  //...
  externalsType: 'promise'
};

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