webpack-babel-multi-target-plugin

This project, inspired by Phil Walton's article Deploying es2015 Code in Production Today, adds tooling to simplify the additional configuration with a Webpack plugin, BabelMultiTargetPlugin.

Setup and Configuration

Using the plugin requires making a few small changes to your existing webpack configuration:

• Replace any instances of 'babel-loader' with BabelMultiTargetPlugin.loader()

  • Do not use a Loader configuration object here - see Options Reference below for information on customizing options for 'babel-loader'

• Add a loader rule for .js files if there isn't one already:

{
  test: /\.js$/,
  use: [
    BabelMultiTargetPlugin.loader(),
  ],
},

Note: The above example intentionally does not exclude node_modules.

• Set resolve.mainFields to favor modern ES modules, which allows webpack to load the most modern source possible. There are several intersecting de-facto standards flying around, so this should cover as much as possible:

mainFields: [

  // rxjs and Angular Package Format
  // these are generally shipped as a higher ES language level than `module`
  'es2015',
  'esm2015',
  'fesm2015',

  // current leading de-facto standard - see https://github.com/rollup/rollup/wiki/pkg.module
  'module',

  // previous de-facto standard, superceded by `module`, but still in use by some packages
  'jsnext:main',

  // Angular Package Format - lower ES level
  'esm5',
  'fesm5',

  // standard package.json fields
  'browser',
  'main',
],

• Add an instance of BabelMultiTargetPlugin to the webpack configuration's plugins property

• BabelMultiTargetPlugin does not require any configuration - but can be customized (see Options Reference below)

• Remove any .babelrc - see Options Reference below for setting preset options

• Remove any references to babel-loader from your package.json - it is a direct dependency of webpack-babel-multi-target-plugin, and may cause unexpected issues if there are duplicate instances due to a version mismatch

• Remove any path or pattern matching node_modules from the exclude property of any rules using BabelMultiTargetPlugin.loader()

• TypeScript

  • Loader rules must use BabelMultiTargetPlugin.loader() after your compiler loader (remember, loaders are run bottom to top)
  • Set tsconfig to target es6 or higher

• Vue

  • Replace 'vue-loader' with BabelMultiTargetPlugin.loader('vue-loader')

• expose-loader

  • Rules using expose-loader must be defined before rules using BabelMultiTargetPlugin.loader()
  • Do not import/require libraries exposed with expose-loader - either reference them from the global scope, or do not use expose-loader. You may also need to use Webpack's ProvidePlugin.

Upgrading from v1.x

• Change usages of BabelMultiTargetPlugin.loader to BabelMultiTargetPlugin.loader()

Usage with ES6 Dynamic Imports

When using ES6's import(...) syntax, you may use Webpack's built-in chunk naming syntax to control the naming of the resulting chunk:

import(/* webpackChunkName: "my-dynamic-import" */'./some-other-module')

When working with imports that use an expression within the import syntax, BabelMultiTargetPlugin adds the [resource] tag to allow better control over the naming of the resulting chunk. The [resource] tag will be replaced by the relative path of the imported module, minus the file extension.

/*
 * ./src/
 *   - plugins
 *     - a
 *       plugin.js
*      - b
*        plugin.js
 *  
 */

// ./src/loader.js
import(/* webpackChunkName: "[resource]" */`./plugins/${plugin}/plugin.js`)

In the above example, the resulting chunks for the plugin files would be (depending on the target configuration):

• a-plugin.js (legacy bundle for ./src/plugins/a/plugin.js)
• a-plugin.modern.js (modern bundle for ./src/plugins/a/plugin.js)
• b-plugin.js (legacy bundle for ./src/plugins/b/plugin.js)
• b-plugin.modern.js (modern bundle for ./src/plugins/b/plugin.js)

// webpack.config.js

const BabelMultiTargetPlugin = require('webpack-babel-multi-target-plugin').BabelMultiTargetPlugin
const NamedLazyChunksPlugin =  require('webpack-babel-multi-target-plugin').NamedLazyChunksPlugin

module.exports = {
  ...
  
  plugins: [
    new BabelMultiTargetPlugin(),
    new NamedLazyChunksPlugin(),
  ],
}

NamedLazyChunkPlugin can also be used with plain ES6 Dynamic Imports as an alternative to Webpack's chunk naming syntax.

Configuration Defaults

BabelMultiTargetPlugin does not require any options to be set. The default behavior is:

• Generate "modern" and "legacy" bundles.

• The "modern" bundle assets will have their filenames appended with .modern, while the "legacy" bundle assets will remain the same. This enables these assets to be deployed without breaking anything since it will still have the required polyfills.

• "modern" browsers are the last 2 versions of each browser, excluding versions that don't support <script type="module">

Options Reference

• babel.plugins (string[]) - a list of Babel plugins to use. @babel/plugin-syntax-dynamic-import is included automatically.

• babel.presets (string[]) - a list of Babel presets to use. @babel/preset-env is included automatically.

• babel.presetOptions (BabelPresetOptions) - options passed to @babel/preset-env. See Babel's preset-env options documentation for more info.

  • Default: { modules: false, useBuiltIns: 'usage' }
  • IMPORTANT: modules is forced to false to avoid problems with transformed commonjs modules

• doNotTarget (RegExp[]) - an array of RegExp patterns for modules which will be excluded from targeting (see How It Works below)

• exclude (RegExp[]) - an array of RegExp patterns for modules which will be excluded from transpiling

• targets ({ [browserProfile: string]: BabelTargetOptions }) - a map of browser profiles to target definitions. This is used to control the transpilation for each browser target. See Configuration Defaults above for default values.

  • targets[browserProfile].key (string) - Used internally to identify the target, and is appended to the filename of an asset if tagAssetsWithKey is set to true. Defaults to browserProfile if not set.
  • targets[browserProfile].tagAssetsWithKey (boolean) - Determines whether the key is appended to the filename of the target's assets. Defaults to true for the "modern" target, and false for the "legacy" target. Only one target can have this property set to false.
  • targets[browserProfile].browsers Defines the browserslist used by @babel/preset-env for this target.
  • targets[browserProfile].esModule (boolean) - Determines whether this target can be referenced by a <script type="module"> tag. Only one target may have this property set to true.
  • targets[browserProfile].noModule (boolean) - Determines whether this target can be referenced by a <script nomodule> tag. Only one target may have this property set to true.
  • targets[browserProfile].additionalModules (string[]) - An optional array of modules that will be prepended to the entry module for the target.

• safari10NoModuleFix | safari10NoModuleFix.mode (boolean | 'external', 'inline' | 'inline-data' | 'inline-data-base64' ) - Embeds a polyfill/workaround to allow the nomodule attribute to function correctly in Safari 10.1. See #9 for more information.

  • false - disabled (default)
  • true | 'inline' - adds the nomodule fix in an inline script (HtmlWebpackPlugin only)
  • 'inline-data' - adds the nomodule fix using a script tag with a data url (HtmlWebpackPlugin only)
  • 'inline-data-base64' - adds the nomodule fix using a script tag with a base64-encoded data url (HtmlWebpackPlugin only)
  • 'external' - adds the nomodule fix as a separate file linked with a <script src> tag

• safari10NoModuleFix.inject ('head' | 'body') - element to inject the script tag into (HtmlWebpackPlugin only)

  • Default: 'head'
  • When using 'body' the tag will be inserted before other script tags.

• safari10NoModuleFix.minify (boolean) - minify the fix (uses terser with default settings)

  • Default: false (to maintain compatibility with older versions of the plugin without this option)

• normalizeModuleIds: (boolean) - EXPERIMENTAL. Removes the babel targeting query from module ids so they use what the module id would be without using BabelMultiTargetPlugin, and adds a check to webpack's bootstrapping code that stops bundle code from executing if it detects that webpack has already been bootstrapped elsewhere. This has the effect of preventing duplicate modules from loading in instances where the browser loads both bundles (e.g. Safari 10.1).

Configuration Examples

Basic Usage

// webpack.config.js

const BabelMultiTargetPlugin = require('webpack-babel-multi-target-plugin').BabelMultiTargetPlugin;

module.exports = {

    entry: 'src/main.js',

    resolve: {
        mainFields: [
            'es2015',
            'module',
            'main',
        ],
    },

    module: {
        rules: [
            {
                test: /\.js$/,
                use: [
                    BabelMultiTargetPlugin.loader(),
                ],
            },
        ],
    },

    plugins: [
        new BabelMultiTargetPlugin(),
    ],

};

TypeScript

// webpack.config.js

const BabelMultiTargetPlugin = require('webpack-babel-multi-target-plugin').BabelMultiTargetPlugin;

module.exports = {

    entry: 'src/main.ts',

    resolve: {
        mainFields: [
            'es2015',
            'module',
            'main',
        ],
    },

    module: {
        rules: [
            {
                test: /\.js$/,
                use: [
                    BabelMultiTargetPlugin.loader(),
                ],
            },
            {
                test: /\.ts$/,
                use: [
                    BabelMultiTargetPlugin.loader(),
                    'ts-loader'
                ],
                options: {
                    useCache: true,
                    cacheDirectory: 'node_modules/.cache/ts-loader',
                },
            },
        ],
    },

    plugins: [
        new BabelMultiTargetPlugin(),
    ],

};

With Options

// webpack.config.js

const BabelMultiTargetPlugin = require('webpack-babel-multi-target-plugin').BabelMultiTargetPlugin;

module.exports = {

    entry: 'src/main.js',

    resolve: {
        mainFields: [
            'es2015',
            'module',
            'main',
        ],
    },

    module: {
        rules: [
            {
                test: /\.js$/,
                use: [
                    BabelMultiTargetPlugin.loader(),
                ],
            },
        ],
    },

    plugins: [
        new BabelMultiTargetPlugin({

            babel: {
                // babel preset-env plugin options go here
            },

            // excludes the untargetable-library module from being targeted
            doNotTarget: [
                /node_modules\/untargetable-library/,
            ],

            // excludes the transpiling-trouble module from being transpiled
            exclude: [
                /node_modules\/transpiling-trouble/
            ],

            // swap which target gets the name appended
            targets: {

                // results in the "modern" bundle being output as main.js
                // the default is main.modern.js
                modern: {
                    tagAssetsWithKey: false,
                },

                // results in the "legacy" bundle being output as main.old-and-broke.js
                // the default is main.js
                legacy: {
                    key: 'old-and-broke',
                    tagAssetsWithKey: true,
                },
            },
        }),
    ],

};

Don't Transpile ES5-only Libraries

Some libraries may cause runtime errors if they are transpiled - often, they will already have been transpiled by Babel as part of the author's publishing process. These errors may look like:

Cannot assign to read only property 'exports' of object '\#\<Object\>'

or

__webpack_require__(...) is not a function

These libraries most likely need to be excluded from Babel's transpilation. While the plugin will automatically attempt to filter out CommonJs modules, you can also specify libraries to be excluded in the BabelMultiTargetPlugin constructor:

new BabelMultiTargetPlugin({
    exclude: [
        /node_modules\/some-es5-library/,
        /node_modules\/another-es5-library/,
    ],
});

Example Projects

Several simple use cases are provided to show how the plugin works.

Install Example Project Dependencies

# installs dependencies for all example projects; requires bash and yarn
yarn setup

Build the Example Projects

# builds all example projects
yarn examples

# build just the specified example projects
yarn es6-plain typescript-plain

Example Project Dev Server

# builds and serves all example projects
yarn start

# builds and serves just the specified example projects
yarn start es6-plain typescript-plain

Note that when running all example projects concurrently, you may need to increase Node's memory limit:

NODE_OPTIONS="--max-old-space-size=8192" yarn start

Examples will be available at http://HOST:PORT/examples/EXAMPLE_NAME.

How It Works

This plugin works by effectively duplicating each entry point, and giving it a target. Each target corresponds to a browser definition that is passed to Babel. As the compilation processes each entry point, the target filters down from the entry point through each of its dependencies. Once the compilation is complete, any CSS outputs are merged into a single module so they are not duplicated (since CSS will be the same regardless of ES supported level). If HtmlWebpackPlugin is being used, the script tags are updated to use the appropriate type="module" and nomodule attributes.

Transpiling node_modules

In order to have the greatest possible positive effect, the compilation must be able to start with the high possible ES level of source code. This is why the extra entries were added to the mainFields array, and why node_modules is not excluded from loader rules. This ensures that even dependencies can take advantage of being able to be bundled with ES6 features and syntax, and the more verbose syntax and polyfill-laden only included for legacy browsers.

Blind Targeting

In some circumstances, such as lazy-loaded routes and modules with Angular, Vue, and ES6 dynamic imports, it may not be possible to determine the entry point of a module. In these cases, the plugin will assign the module a target on its own. It does this by creating an array of the targets, and removing and assigning one target each time it encounters a given resource.

If you encounter a BlindTargetingError while attempting to use this plugin, please create an issue with a simple reproduction.

Benefits

• Automatically sets up your index HTML files with both "modern" and "legacy" bundles

• Uses ES2015 source when available, and attempts to automatically avoid re-transpiling ES5/CommonJs code

• Avoid using between 30-70 KB of polyfill code on browsers that don't need them (depends on project size and features used)

Caveats

• Increased build time - since the plugin duplicates entry points, everything has to be done twice. This can be helped with appropriate cache configurations where they are available (Babel, TypeScript, etc), but it may make sense to avoid using this plugin during development.

• May not play nice with hard-source-webpack-plugin

• Code Splitting - Since CommonJs dependencies can be shared between "modern" and "legacy" bundles, apps with multiple entries or lazy-loaded modules may end up with a large number of "vendor" chunks.

Testing

The output generated by this plugin is tested on the following browsers courtesy of BrowserStack:

• Chrome
• Firefox
• Edge
• Safari (including 10.1 on Mac OS and 10.3 on iOS)
• IE 11