Webpacker

Webpacker makes it easy to use the JavaScript pre-processor and bundlerWebpack v5to manage application-like JavaScript in Rails. It can coexist with the asset pipeline,leaving Webpack responsible solely for app-like JavaScript, or it can be used exclusively, making it also responsible for images, fonts, and CSS.

NOTE: The master branch now hosts the code for v6.x.x. Please refer to 5-x-stable branch for 5.x documentation.

Table of Contents

• Prerequisites
• Features
  • Optional support
• Installation
  • Usage
    • Server-Side Rendering (SSR)
  • Development
  • Webpack Configuration
  • Babel Configuration
  • Integrations
    • React
    • CoffeeScript
    • TypeScript
    • CSS
    • Postcss
    • Sass
    • Less
    • Stylus
    • Other frameworks
  • Custom Rails environments
  • Upgrading
• Paths
  • Additional paths
• Deployment
• Troubleshooting
• Contributing
• License

Prerequisites

• Ruby 2.4+
• Rails 5.2+
• Node.js 12.13.0+ || 14+
• Yarn

Features

• Webpack v5
• ES6 with babel
• Automatic code splitting using multiple entry points
• Asset compression, source-maps, and minification
• CDN support
• Rails view helpers
• Extensible and configurable

Optional support

requires extra packages to be installed

• Stylesheets - Sass, Less, Stylus and Css, PostCSS
• CoffeeScript
• TypeScript
• React

Installation

You can configure a new Rails application with Webpacker right from the start using the -j webpack option:

rails new myapp -j webpack

Or you can add it later by changing your Gemfile:

# Gemfile
gem 'webpacker', '~> 6.0'

# OR if you prefer to use master
gem 'webpacker', git: 'https://github.com/rails/webpacker.git'
yarn add https://github.com/rails/webpacker.git

Then running the following to install Webpacker:

./bin/bundle install
./bin/rails webpacker:install

When package.json and/or yarn.lock changes, such as when pulling down changes to your local environment in a team settings, be sure to keep your NPM packages up-to-date:

yarn install

Usage

Once installed, you can start writing modern ES6-flavored JavaScript apps right away:

app/javascript:
  # Only Webpack entry files here
  └── application.js
  └── application.css
  └── src:
  │   └── my_component.js
  └── stylesheets:
  │   └── my_styles.css
  └── images:
      └── logo.svg

You can then link the JavaScript pack in Rails views using the javascript_pack_tag helper. If you have styles imported in your pack file, you can link them by using stylesheet_pack_tag:

<%= javascript_pack_tag 'application' %>
<%= stylesheet_pack_tag 'application' %>

The javascript_pack_tag and stylesheet_pack_tag helpers will include all the transpiledpacks with the chunks in your view, which creates html tags for all the chunks.

The result looks like this:

<%= javascript_pack_tag 'calendar', 'map', 'data-turbolinks-track': 'reload' %>

<script src="/packs/vendor-16838bab065ae1e314.js" data-turbolinks-track="reload" defer></script>
<script src="/packs/calendar~runtime-16838bab065ae1e314.js" data-turbolinks-track="reload" defer></script>
<script src="/packs/calendar-1016838bab065ae1e314.js" data-turbolinks-track="reload" defer"></script>
<script src="/packs/map~runtime-16838bab065ae1e314.js" data-turbolinks-track="reload" defer></script>
<script src="/packs/map-16838bab065ae1e314.js" data-turbolinks-track="reload" defer></script>

Important: Pass all your pack names as multiple arguments, not multiple calls, when using javascript_pack_tag and the **stylesheet_pack_tag. Otherwise, you will get duplicated chunks on the page. Be especially careful if you might be calling these view helpers from your view, partials, and the layout for a page. You will need some logic to ensure you call the helpers only once with multiple arguments.

<%# DO %>
<%= javascript_pack_tag 'calendar', 'map' %>
<%= stylesheet_pack_tag 'calendar', 'map' %>

<%# DON'T %>
<%= javascript_pack_tag 'calendar' %>
<%= javascript_pack_tag 'map' %>
<%= stylesheet_pack_tag 'calendar' %>
<%= stylesheet_pack_tag 'map' %>

If you want to link a static asset for <img /> tag, you can use the asset_pack_path helper:

<img src="<%= asset_pack_path 'images/logo.svg' %>" />

Or use the dedicated helper:

<%= image_pack_tag 'application.png', size: '16x10', alt: 'Edit Entry' %>
<%= image_pack_tag 'picture.png', srcset: { 'picture-2x.png' => '2x' } %>

If you want to create a favicon:

<%= favicon_pack_tag 'mb-icon.png', rel: 'apple-touch-icon', type: 'image/png' %>

If you want to preload a static asset in your <head>, you can use the preload_pack_asset helper:

<%= preload_pack_asset 'fonts/fa-regular-400.woff2' %>

If you want to use images in your stylesheets:

.foo {
  background-image: url('../images/logo.svg')
}

Defer for javascript_pack_tag

Note, the default of "defer" for the javascript_pack_tag. You can override that to false. If you expose jquery globally with expose-loader, by using import $ from "expose-loader?exposes=$,jQuery!jquery" in your app/packs/entrypoints/application.js, pass the option defer: false to your javascript_pack_tag.

Server-Side Rendering (SSR)

Note, if you are using server-side rendering of JavaScript with dynamic code-splitting, as is often done with extensions to Webpacker, like React on Rails, your JavaScript should create the link prefetch HTML tags that you will use, so you won't need to use to asset_pack_path in those circumstances.

Note: In order for your styles or static assets files to be available in your view, you would need to link them in your "pack" or entry file. Otherwise, Webpack won't know to package up those files.

Development

Webpacker ships with two binstubs: ./bin/webpack and ./bin/webpack-dev-server. Both are thin wrappers around the standard webpack.js and webpack-dev-server.js executables to ensure that the right configuration files and environmental variables are loaded based on your environment.

In development, Webpacker compiles on demand rather than upfront by default. This happens when you refer to any of the pack assets using the Webpacker helper methods. This means that you don't have to run any separate processes. Compilation errors are logged to the standard Rails log. However, this auto-compilation happens when a web request is made that requires an updated webpack build, not when files change. Thus, that can be painfully slow for front-end development in this default way. Instead, you should either run the bin/webpack --watch or run ./bin/webpack-dev-server

If you want to use live code reloading, or you have enough JavaScript that on-demand compilation is too slow, you'll need to run ./bin/webpack-dev-server or ruby ./bin/webpack-dev-server. Windows users will need to run these commands in a terminal separate from bundle exec rails s. This process will watch for changes in the relevant files, defined by webpacker.yml configuration settings for source_path, source_entry_path, and additional_paths, and it will then automatically reload the browser to match. This feature is also known as Hot Module Replacement.

# webpack dev server
./bin/webpack-dev-server

# watcher
./bin/webpack --watch --progress

# standalone build
./bin/webpack --progress

# Help
./bin/webpack help

# Version
./bin/webpack version

# Info
./bin/webpack info

Once you start this webpack development server, Webpacker will automatically start proxying all webpack asset requests to this server. When you stop this server, Rails will detect that it's not running and Rails will revert back to on-demand compilation if you have the compile option set to true in your config/webpacker.yml

You can use environment variables as options supported by webpack-dev-server in the form WEBPACKER_DEV_SERVER_<OPTION>. Please note that these environmental variables will always take precedence over the ones already set in the configuration file, and that the same environmental variables must be available to the rails server process.

WEBPACKER_DEV_SERVER_HOST=example.com WEBPACKER_DEV_SERVER_INLINE=true WEBPACKER_DEV_SERVER_HOT=false ./bin/webpack-dev-server

By default, the webpack dev server listens on localhost in development for security purposes. However, if you want your app to be available over local LAN IP or a VM instance like vagrant, you can set the host when running ./bin/webpack-dev-server binstub:

WEBPACKER_DEV_SERVER_HOST=0.0.0.0 ./bin/webpack-dev-server

Note: You need to allow webpack-dev-server host as an allowed origin for connect-src if you are running your application in a restrict CSP environment (like Rails 5.2+). This can be done in Rails 5.2+ in the CSP initializer config/initializers/content_security_policy.rb with a snippet like this:

Rails.application.config.content_security_policy do |policy|
  policy.connect_src :self, :https, 'http://localhost:3035', 'ws://localhost:3035' if Rails.env.development?
end

Note: Don't forget to prefix ruby when running these binstubs on Windows

Webpack Configuration

Webpacker gives you a default set of configuration files for test, development and production environments in config/webpack/*.js. You can configure each individual environment in their respective files or configure them all in the baseconfig/webpack/base.js file.

By default, you don't need to make any changes to config/webpack/*.js files since it's all standard production-ready configuration. However, if you do need to customize or add a new loader, this is where you would go.

Here is how you can modify webpack configuration:

You might add separate files to keep your code more organized.

// config/webpack/custom.js
module.exports = {
  resolve: {
    alias: {
      jquery: 'jquery/src/jquery',
      vue: 'vue/dist/vue.js',
      React: 'react',
      ReactDOM: 'react-dom',
      vue_resource: 'vue-resource/dist/vue-resource'
    }
  }
}

Then require this file in your config/webpack/base.js:

// config/webpack/base.js
const { webpackConfig, merge } = require('@rails/webpacker')
const customConfig = require('./custom')

module.exports = merge(webpackConfig, customConfig)

If you need access to configs within Webpacker's configuration, you can import them like so:

// config/webpack/base.js
const { webpackConfig } = require('@rails/webpacker')

console.log(webpackConfig.output_path)
console.log(webpackConfig.source_path)

// Or to print out your whole webpack configuration
console.log(JSON.stringify(webpackConfig, undefined, 2))

Babel configuration

By default, you will find the Webpacker preset in your package.json.

"babel": {
  "presets": [
    "./node_modules/@rails/webpacker/package/babel/preset.js"
  ]
},

Optionally, you can change your Babel configuration by removing these lines in your package.json and add a Babel configuration file in your project.

Integrations

Webpacker out of the box supports JS and static assets (fonts, images etc.) compilation. To enable support for CoffeeScript or TypeScript install relevant packages:

React

yarn add react react-dom @babel/preset-react

...if you are using typescript, update your tsconfig.json

{
  "compilerOptions": {
    "declaration": false,
    "emitDecoratorMetadata": true,
    "experimentalDecorators": true,
    "lib": ["es6", "dom"],
    "module": "es6",
    "moduleResolution": "node",
    "sourceMap": true,
    "target": "es5",
    "jsx": "react",
    "noEmit": true
  },
  "exclude": ["**/*.spec.ts", "node_modules", "vendor", "public"],
  "compileOnSave": false
}

CoffeeScript

yarn add coffeescript coffee-loader

TypeScript

yarn add typescript @babel/preset-typescript

Babel won’t perform any type-checking on TypeScript code. To optionally use type-checking run:

yarn add fork-ts-checker-webpack-plugin

Add tsconfig.json

{
  "compilerOptions": {
    "declaration": false,
    "emitDecoratorMetadata": true,
    "experimentalDecorators": true,
    "lib": ["es6", "dom"],
    "module": "es6",
    "moduleResolution": "node",
    "baseUrl": ".",
    "paths": {
      "*": ["node_modules/*", "app/packs/*"]
    },
    "sourceMap": true,
    "target": "es5",
    "noEmit": true
  },
  "exclude": ["**/*.spec.ts", "node_modules", "vendor", "public"],
  "compileOnSave": false
}

Then modify the webpack config to use it as a plugin:

// config/webpack/base.js
const { webpackConfig, merge } = require("@rails/webpacker");
const ForkTSCheckerWebpackPlugin = require("fork-ts-checker-webpack-plugin");

module.exports = merge(webpackConfig, {
  plugins: [new ForkTSCheckerWebpackPlugin()],
});

CSS

To enable CSS support in your application, add following packages:

yarn add css-loader style-loader mini-css-extract-plugin css-minimizer-webpack-plugin

Optionally, add the CSS extension to webpack config for easy resolution.

// config/webpack/base.js
const { webpackConfig, merge } = require('@rails/webpacker')
const customConfig = {
  resolve: {
    extensions: ['.css']
  }
}

module.exports = merge(webpackConfig, customConfig)

To enable PostCSS, Sass or Less support, add CSS support first andthen add the relevant pre-processors:

Postcss

yarn add postcss postcss-loader

Optionally add these two plugins if they are required in your postcss.config.js:

yarn add postcss-preset-env postcss-flexbugs-fixes

Sass

yarn add sass sass-loader

Less

yarn add less less-loader

Stylus

yarn add stylus stylus-loader

Other frameworks

Please follow webpack integration guide for relevant framework or library,

1. Svelte
2. Angular
3. Vue

For example to add Vue support:

// config/webpack/rules/vue.js
const { VueLoaderPlugin } = require('vue-loader')

module.exports = {
  module: {
    rules: [
      {
        test: /\.vue$/,
        loader: 'vue-loader'
      }
    ]
  },
  plugins: [new VueLoaderPlugin()],
  resolve: {
    extensions: ['.vue']
  }
}

// config/webpack/base.js
const { webpackConfig, merge } = require('@rails/webpacker')
const vueConfig = require('./rules/vue')

module.exports = merge(vueConfig, webpackConfig)

Custom Rails environments

Out of the box Webpacker ships with - development, test and production environments in config/webpacker.yml however, in most production apps extra environments are needed as part of deployment workflow. Webpacker supports this out of the box from version 3.4.0+ onwards.

You can choose to define additional environment configurations in webpacker.yml,

staging:
  <<: *default

  # Production depends on precompilation of packs prior to booting for performance.
  compile: false

  # Cache manifest.json for performance
  cache_manifest: true

  # Compile staging packs to a separate directory
  public_output_path: packs-staging

Otherwise Webpacker will use production environment as a fallback environment for loading configurations. Please note, NODE_ENV can either be set to production, development or test. This means you don't need to create additional environment files inside config/webpacker/* and instead use webpacker.yml to load different configurations using RAILS_ENV.

For example, the below command will compile assets in production mode but will use staging configurations from config/webpacker.yml if available or use fallback production environment configuration:

RAILS_ENV=staging bundle exec rails assets:precompile

And, this will compile in development mode and load configuration for cucumber environment if defined in webpacker.yml or fallback to production configuration

RAILS_ENV=cucumber NODE_ENV=development bundle exec rails assets:precompile

Please note, binstubs compiles in development mode however rake tasks compiles in production mode.

# Compiles in development mode unless NODE_ENV is specified, per the binstub source
./bin/webpack
./bin/webpack-dev-server

# Compiles in production mode by default unless NODE_ENV is specified, per `lib/tasks/webpacker/compile.rake`
bundle exec rails assets:precompile
bundle exec rails webpacker:compile

Upgrading

You can run following commands to upgrade Webpacker to the latest stable version. This process involves upgrading the gem and related JavaScript packages:

# check your Gemfile for version restrictions
bundle update webpacker

# overwrite your changes to the default install files and revert any unwanted changes from the install
rails webpacker:install

# yarn 1 instructions
yarn upgrade @rails/webpacker --latest
yarn upgrade webpack-dev-server --latest

# yarn 2 instructions
yarn up @rails/webpacker@latest
yarn up webpack-dev-server@latest

# Or to install the latest release (including pre-releases)
yarn add @rails/webpacker@next

Also, consult the CHANGELOG for additional upgrade links.

Paths

By default, Webpacker ships with simple conventions for where the JavaScript app files and compiled webpack bundles will go in your Rails app. All these options are configurable from config/webpacker.yml file.

The configuration for what webpack is supposed to compile by default rests on the convention that every file in app/packs/entrypoints/*(default) or whatever path you set for source_entry_path in the webpacker.yml configuration is turned into their own output files (or entry points, as webpack calls it). Therefore you don't want to put anything inside packs directory that you do not want to be an entry file. As a rule of thumb, put all files you want to link in your views inside "packs" directory and keep everything else under app/packs.

Suppose you want to change the source directory from app/packs to frontend and output to assets/packs. This is how you would do it:

# config/webpacker.yml
source_path: frontend # packs are in frontend/packs
public_output_path: assets/packs # outputs to => public/assets/packs

Similarly you can also control and configure webpack-dev-server settings from config/webpacker.yml file:

# config/webpacker.yml
development:
  dev_server:
    host: localhost
    port: 3035

If you have hmr turned to true, then the stylesheet_pack_tag generates no output, as you will want to configure your styles to be inlined in your JavaScript for hot reloading. During production and testing, the stylesheet_pack_tag will create the appropriate HTML tags.

Additional paths

If you are adding Webpacker to an existing app that has most of the assets inside app/assets or inside an engine, and you want to share that with webpack modules, you can use the additional_paths option available in config/webpacker.yml. This lets youadd additional paths that webpack should look up when resolving modules:

additional_paths: ['app/assets', 'vendor/assets']

You can then import these items inside your modules like so:

// Note it's relative to parent directory i.e. app/assets
import 'stylesheets/main'
import 'images/rails.png'

Note: Please be careful when adding paths here otherwise it will make the compilation slow, consider adding specific paths instead of whole parent directory if you just need to reference one or two modules

Also note: While importing assets living outside your source_path defined in webpacker.yml (like, for instance, assets under app/assets) from within your packs using relative paths like import '../../assets/javascripts/file.js' will work in development, Webpacker won't recompile the bundle in production unless a file that lives in one of it's watched paths has changed (check out Webpacker::Compiler#watched_files_digest). That's why you'd need to add app/assets to the additional_paths as stated above and use import 'javascripts/file.js' instead.

Deployment

Webpacker hooks up a new webpacker:compile task to assets:precompile, which gets run whenever you run assets:precompile. If you are not using Sprockets, webpacker:compile is automatically aliased to assets:precompile. Similar to sprockets both rake tasks will compile packs in production mode but will use RAILS_ENV to load configuration from config/webpacker.yml (if available).

When compiling assets for production on a remote server, such as a continuous integration environment, it's recommended to use yarn install --frozen-lockfile to install NPM packages on the remote host to ensure that the installed packages match the yarn.lock file.

If you are using a CDN setup, webpacker will use the configured asset host value to prefix URLs for images or font icons which are included inside JS code or CSS. It is possible to override this value during asset compilation by setting the WEBPACKER_ASSET_HOST environment variable.

Troubleshooting

See the doc page for Troubleshooting.

Contributing

We encourage you to contribute to Webpacker! See CONTRIBUTING for guidelines about how to proceed.

License

Webpacker is released under the MIT License.