Webpack

Configuration

Webpack configuration to help you get started building modern web applications. You write modern javascript using the latest browser features, webpack will optimize your code for production ensure it runs on all supported browsers.

The input for webpack is the same index.html you use for development. Any module scripts in your index are run through webpack and your index is updated with the output from rollup.

See 'config features' for all details. See the extending section for customization, such as supporting non-standard syntax or adding babel plugins.

Setup

New project

npm init @open-wc

Existing project

npm init @open-wc
# Upgrade > Building > Webpack

Manual setup

  1. Install the required dependencies:
npm i -D @open-wc/building-webpack webpack webpack-cli es-dev-server
  1. Create a file called webpack.config.js and pass in your app's js entry point and index.html. Pick the config you need below:
const path = require('path');
const createDefaultConfig = require('@open-wc/building-webpack/modern-config');

// if you need to support IE11 use "modern-and-legacy-config" instead.
// const createDefaultConfig = require('@open-wc/building-webpack/modern-and-legacy-config');

module.exports = createDefaultConfig({
  input: path.resolve(__dirname, './index.html'),
});
  1. Create an index.html:
<!doctype html>
<html>
  <head></head>
  <body>
    <your-app></your-app>

    <script type="module" src="./src/your-app.js"></script>
  </body>
</html>

We use webpack-index-html-plugin. Contrary to other webpack plugins, you do need to include your app's module entrypoint in your index.html. This allows you to use the same index during development and when building.

  1. Add the following commands to your package.json:
{
  "scripts": {
    "build": "webpack --mode production",
    "start:build": "es-dev-server --app-index dist/index.html --open",
  }
}
  • start runs your app for development, reloading on file changes
  • start:build runs your app after it has been built using the build command
  • build builds your app and outputs it in your dist directory

Browser support

modern-config.js creates a single build of your app for modern browsers (by default last 2 of major browsers). This is recommended if you only need to support modern browsers, otherwise you will need to ship compatibility code for browsers which don't need it.

modern-and-legacy-config.js creates two builds of your app. A modern build like the above, and a legacy build for IE11. Additional code is injected to load polyfills and the correct version of your app. This is recommended if you need to support IE11.

Config features

All configs:

  • resolve bare imports (import { html } from 'lit-html')
  • preserve import.meta.url value from before bundling
  • minify + treeshake js
  • minify html and css in template literals

modern-config.js:

  • single build output
  • compatible with any browser which supports Web Components

modern-and-legacy-config.js:

  • Two build outputs:
    • Modern:
      • compatible with modern browsers (default: last 2 chrome, firefox safari and edge)
      • does not penalize users with modern browser with compatibility code for IE11
    • Legacy:
      • compatible down to IE11
      • babel transform down to IE11 (es5)
      • core js babel polyfills (Array.from, String.prototype.includes etc.)
      • webcomponentsjs polyfills
      • URL polyfill
      • fetch polyfill

See below for more configuration options.

Customizing the babel config

You can define your own babel plugins by adding a .babelrc or babel.config.js to your project. See babeljs config for more information.

For example to add support for class properties:

{
  "plugins": [
    "@babel/plugin-proposal-class-properties"
  ]
}

Adjusting browser support for the modern build

The legacy build targets IE11, which is the earliest browser supported by the webcomponents polyfill. For the modern build we target the lates 2 versions of the major browsers (chrome, firefox, safari and edge).

You can adjust this by adding a browserslist configuration. For example by adding a .browserslistrc file to your project, or adding an entry to your package.json. See the browserslist documentation for more information.

Note: you should not add IE11 or other very early browsers as a target in your browserslist, as it would result in a broken modern build because it makes some assumptions around browser support. Use the --legacy flag for legacy builds.

Extending the webpack config

A webpack config is an object. To extend it, we recommend using webpack-merge to ensure plugins are merged correctly. For example to adjust the output folder:

const merge = require('webpack-merge');
const createDefaultConfig = require('@open-wc/building-webpack/modern-config');

const config = createDefaultConfig({
  input: path.resolve(__dirname, './index.html'),
});

module.exports = merge(config, {
  output: {
    path: 'build'
  },
});

If you use modern-and-legacy-config.js, it is actually an array of configs so that webpack outputs a modern and a legacy build. Simply map over the array to adjust both configs:

const merge = require('webpack-merge');
const createDefaultConfigs = require('@open-wc/building-webpack/modern-and-legacy-config');

const configs = createDefaultConfigs({
  input: path.resolve(__dirname, './index.html'),
});

module.exports = configs.map(config => merge(config, {
  output: {
    path: 'build'
  },
}));

Common extensions

Some extensions or plugins add non-native or experimental features to your code. This can be bad for the maintenance of your code in the long term, we therefore don't recommend it unless you know what you're doing.

Customizing index.html output

If you need to customize the output of your index.html you can pass extra options to webpack-index-html-plugin:

const merge = require('webpack-merge');
const createDefaultConfig = require('@open-wc/building-webpack/modern-config');

module.exports = createDefaultConfig({
  input: path.resolve(__dirname, './index.html'),
  webpackIndexHTMLPlugin: {
    polyfills: {
      fetch: false,
      intersectionObserver: true,
    },
  },
});

See the documentation for all options.

non index.html entrypoint

By default we look for an index.html as entrypoint. If want to use regular entrypoints you will need to provide your index.html for output manually:

const merge = require('webpack-merge');
const createDefaultConfig = require('@open-wc/building-webpack/modern-config');

module.exports = createDefaultConfig({
  input: path.resolve(__dirname, './my-app.js'),
  webpackIndexHTMLPlugin: {
    template: ({ assets, entries, legacyEntries, variation }) => `
      <html>
        <head></head>
        <body></body>
      </html>
    `,
  },
});

Adding or removing polyfills

By default we polyfill core-js, webcomponentsjs and fetch. It is possile to add or remove polyfills by passing webpack-index-html configuration like above:

const merge = require('webpack-merge');
const createDefaultConfig = require('@open-wc/building-webpack/modern-config');

module.exports = createDefaultConfig({
  input: path.resolve(__dirname, './index.html'),
  webpackIndexHTMLPlugin: {
    polyfills: {
      fetch: false,
      intersectionObserver: true,
      customPolyfills: [
        {
          name: 'my-feature',
          test: "'myFeature' in window",
          path: require.resolve('my-feature-polyfill/dist/bundled.js'),
        },
      ],
    },
  },
});

See the documentation for more information.

Copy assets

Web apps often include assets such as css files and images. These are not part of your regular dependency graph, so they need to be copied into the build directory.

copy-webpack-plugin is a popular plugin fo this.

const path = require('path');
const merge = require('webpack-merge');
const CopyWebpackPlugin = require('copy-webpack-plugin');
const createDefaultConfigs = require('@open-wc/building-webpack/modern-and-legacy-config');

const configs = createDefaultConfigs({
  input: path.resolve(__dirname, './index.html'),
});

// with modern-and-legacy-config, the config is actually an array of configs for a modern and
// a legacy build. We don't need to copy files twice, so we aadd the copy job only to the first
// config
module.exports = [
  // add plugin to the first config
  merge(configs[0], {
    plugins: [
      new CopyWebpackPlugin([
        'images/**/*.png',
      ]),
    ],
  }),

  // the second config left untouched
  configs[1],
];

Support typescript

Make sure to prevent any compilation done by the typescript compiler tsconfig.json, as babel and webpack do this for you:

{
  "compilerOptions": {
    "target": "ESNEXT",
    "module": "ESNext",
  }
}

Within webpack there are two options to add typescript support.

1. Babel

We recommend using the babel typescript plugin. Add this to your .babelrc:

{
  "presets": [
    "@babel/preset-typescript"
  ],
}

This the fastest method, as it strips away types during babel transformormation of your code. It will not perform any type checking though. We recommend setting up the type checking as part of your linting setup, so that you don't need to run the typechecker during development for faster builds.

Supporting decorators

Please note that decorators will add non standard syntax to your code.

Due to the way Babel handles decorators and class properties, you'll need to specify the plugins in a specific order with specific options. Here's what you'll need:

{
  "presets": ["@babel/preset-typescript"],
  "plugins": [
    ["@babel/plugin-proposal-decorators", { "decoratorsBeforeExport": true }],
    "@babel/plugin-proposal-class-properties"
  ]
}

2. Plugin

It is also possible to add the webpack typescript plugin, which does typechecking and compiling for you:

const path = require('path');
const merge = require('webpack-merge');
const createDefaultConfigs = require('@open-wc/building-webpack/modern-and-legacy-config');

const configs = createDefaultConfigs({
  input: path.resolve(__dirname, './index.html'),
});

module.exports = configs.map(config =>
  merge(config, {
    module: {
      rules: [{ test: /\.ts$/, loader: 'ts-loader' }],
    },
  }),
);
Last Updated: 1/26/2019, 8:57:17 PM