@wordpress/dependency-extraction-webpack-plugin

Dependency Extraction Webpack Plugin

This webpack plugin serves two purposes:

• Externalize dependencies that are available as script dependencies on modern WordPress sites.
• Add an asset file for each entry point that declares an object with the list of WordPress script dependencies for the entry point. The asset file also contains the current version calculated for the current source code.

This allows JavaScript bundles produced by webpack to leverage WordPress style dependency sharing without an error-prone process of manually maintaining a dependency list.

Consult the webpack website for additional information on webpack concepts.

Installation

Install the module

npm install @wordpress/dependency-extraction-webpack-plugin --save-dev

Usage

Webpack

Use this plugin as you would other webpack plugins:

// webpack.config.js
const DependencyExtractionWebpackPlugin = require( '@wordpress/dependency-extraction-webpack-plugin' );

module.exports = {
  // …snip
  plugins: [
    new DependencyExtractionWebpackPlugin(),
  ]
}

Note: Multiple instances of the plugin are not supported and may produced unexpected results. If you plan to extend the webpack configuration from @wordpress/scripts with your own DependencyExtractionWebpackPlugin, be sure to remove the default instance of the plugin:

const defaultConfig = require( '@wordpress/scripts/config/webpack.config' );
const config = {
  ...defaultConfig,
  plugins: [
    ...defaultConfig.plugins.filter(
      plugin => plugin.constructor.name !== 'DependencyExtractionWebpackPlugin',
    ),
    new DependencyExtractionWebpackPlugin( {
      injectPolyfill: true,
      requestToExternal(request) {
        /* My externals */
      },
    } ),
  ],
};

Each entry point in the webpack bundle will include an asset file that declares the WordPress script dependencies that should be enqueued. Such file also contains the unique version hash calculated based on the file content.

For example:

// Source file entrypoint.js
import { Component } from '@wordpress/element';

// Webpack will produce the output output/entrypoint.js
/* bundled JavaScript output */

// Webpack will also produce output/entrypoint.asset.php declaring script dependencies
<?php return array('dependencies' => array('wp-element'), 'version' => 'dd4c2dc50d046ed9d4c063a7ca95702f');

By default, the following module requests are handled:

Request	Global	Script handle
@babel/runtime/regenerator	regeneratorRuntime	wp-polyfill
@wordpress/*	wp['*']	wp-*
jquery	jQuery	jquery
lodash-es	lodash	lodash
lodash	lodash	lodash
moment	moment	moment
react-dom	ReactDOM	react-dom
react	React	react

Note: This plugin overlaps with the functionality provided by webpack externals. This plugin is intended to extract script handles from bundle compilation so that a list of script dependencies does not need to be manually maintained. If you don't need to extract a list of script dependencies, use the externals option directly.

This plugin is compatible with externals, but they may conflict. For example, adding { externals: { '@wordpress/blob': 'wp.blob' } } to webpack configuration will effectively hide the @wordpress/blob module from the plugin and it will not be included in dependency lists.

Options

An object can be passed to the constructor to customize the behavior, for example:

module.exports = {
  plugins: [
    new DependencyExtractionWebpackPlugin( { injectPolyfill: true } ),
  ]
}

outputFormat

• Type: string
• Default: php

The output format for the generated asset file. There are two options available: 'php' or 'json'.

combineAssets

• Type: boolean
• Default: false

By default, one asset file is created for each entry point. When this flag is set to true, all information about assets is combined into a single assets.(json|php) file generated in the output directory.

combinedOutputFile

• Type: string
• Default: null

This option is useful only when the combineAssets option is enabled. It allows providing a custom output file for the generated single assets file. It's possible to provide a path that is relative to the output directory.

useDefaults

• Type: boolean
• Default: true

Pass useDefaults: false to disable the default request handling.

injectPolyfill

• Type: boolean
• Default: false

Force wp-polyfill to be included in each entry point's dependency list. This would be the same as adding import '@wordpress/polyfill'; to each entry point.

requestToExternal

• Type: function

requestToExternal allows the module handling to be customized. The function should accept a module request string and may return a string representing the global variable to use. An array of strings may be used to access globals via an object path, e.g. wp.i18n may be represented as [ 'wp', 'i18n' ].

requestToExternal provided via configuration has precedence over default external handling. Unhandled requests will be handled by the default unless useDefaults is set to false.

/**
 * Externalize 'my-module'
 *
 * @param {string} request Requested module
 *
 * @return {(string|undefined)} Script global
 */
function requestToExternal( request ) {

  // Handle imports like `import myModule from 'my-module'`
  if ( request === 'my-module' ) {
    // Expect to find `my-module` as myModule in the global scope:
    return 'myModule';
  }
}

module.exports = {
  plugins: [
    new DependencyExtractionWebpackPlugin( { requestToExternal } ),
  ]
}

requestToHandle

• Type: function

All of the external modules handled by the plugin are expected to be WordPress script dependencies and will be added to the dependency list. requestToHandle allows the script handle included in the dependency list to be customized.

If no string is returned, the script handle is assumed to be the same as the request.

requestToHandle provided via configuration has precedence over the defaults. Unhandled requests will be handled by the default unless useDefaults is set to false.

/**
 * Map 'my-module' request to 'my-module-script-handle'
 *
 * @param {string} request Requested module
 *
 * @return {(string|undefined)} Script global
 */
function requestToHandle( request ) {

  // Handle imports like `import myModule from 'my-module'`
  if ( request === 'my-module' ) {
    // `my-module` depends on the script with the 'my-module-script-handle' handle.
    return 'my-module-script-handle';
  }
}

module.exports = {
  plugins: [
    new DependencyExtractionWebpackPlugin( { requestToExternal } ),
  ]
}

requestToExternal and requestToHandle

The functions requestToExternal and requestToHandle allow this module to handle arbitrary modules. requestToExternal is necessary to handle any module and maps a module request to a global name. requestToHandle maps the same module request to a script handle, the strings that will be included in the entrypoint.asset.php files.

WordPress

Enqueue your script as usual and read the script dependencies dynamically:

$script_path       = 'path/to/script.js';
$script_asset_path = 'path/to/script.asset.php';
$script_asset      = file_exists( $script_asset_path )
	? require( $script_asset_path )
	: array( 'dependencies' => array(), 'version' => filemtime( $script_path ) );
$script_url = plugins_url( $script_path, __FILE__ );
wp_enqueue_script( 'script', $script_url, $script_asset['dependencies'], $script_asset['version'] );