Webpacker

Webpacker makes it easy to use the JavaScript pre-processor and bundler webpack 3.x.x+ to manage application-like JavaScript in Rails. It coexists with the asset pipeline, as the primary purpose for webpack is app-like JavaScript, not images, CSS, or even JavaScript Sprinkles (that all continues to live in app/assets).

However, it is possible to use Webpacker for CSS, images and fonts assets as well, in which case you may not even need the asset pipeline. This is mostly relevant when exclusively using component-based JavaScript frameworks.

Table of Contents

• Prerequisites
• Features
• Installation
  • Usage
  • Development
  • Webpack Configuration
  • Custom Rails environments
  • Upgrading
  • Yarn Integrity
• Integrations
  • React
  • Angular with TypeScript
  • Vue
  • Elm
  • Stimulus
  • Coffeescript
  • Erb
• Paths
  • Resolved
  • Watched
• Deployment
• Docs
• License

Prerequisites

• Ruby 2.2+
• Rails 4.2+
• Node.js 6.0.0+
• Yarn 0.25.2+

Features

• webpack 3.x.x
• ES6 with babel
• Automatic code splitting using multiple entry points
• Stylesheets - Sass and CSS
• Images and fonts
• PostCSS - Auto-Prefixer
• Asset compression, source-maps, and minification
• CDN support
• React, Angular, Elm and Vue support out-of-the-box
• Rails view helpers
• Extensible and configurable

Installation

You can either add Webpacker during setup of a new Rails 5.1+ application using new --webpack option:

# Available Rails 5.1+
rails new myapp --webpack

Or add it to your Gemfile:

# Gemfile
gem 'webpacker', '~> 3.5'

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

Finally, run following to install Webpacker:

bundle
bundle exec rails webpacker:install

# OR (on rails version < 5.0)
bundle exec rake webpacker:install

Usage

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

app/javascript:
  ├── packs:
  │   # only webpack entry files here
  │   └── application.js
  └── src:
  │   └── application.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' %>

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

<link rel="prefetch" href="<%= asset_pack_path 'application.css' %>" />
<img src="<%= asset_pack_path 'images/logo.svg' %>" />

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.

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.

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 app/javascript/packs/*.js files and automatically reload the browser to match.

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

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

# standalone build
./bin/webpack

Once you start this development server, Webpacker will automatically start proxying all webpack asset requests to this server. When you stop the server, it'll revert back to on-demand compilation.

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:

  policy.connect_src :self, :https, 'http://localhost:3035', 'ws://localhost:3035' if Rails.env.development?

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

Webpack Configuration

See docs/webpack for modifying webpack configuration and loaders.

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

or, Webpacker will use production environment as a fallback environment for loading configurations. Please note, NODE_ENV can either be set to production or development. 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
./bin/webpack
./bin/webpack-dev-server

# compiles in production mode by default unless NODE_ENV is specified
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:

bundle update webpacker
yarn upgrade @rails/webpacker --latest
yarn add webpack-dev-server@^2.11.1

Yarn Integrity

By default, in development, webpacker runs a yarn integrity check to ensure that all local JavaScript packages are up-to-date. This is similar to what bundler does currently in Rails, but for JavaScript packages. If your system is out of date, then Rails will not initialize. You will be asked to upgrade your local JavaScript packages by running yarn install.

To turn off this option, you will need to override the default by adding a new config option to your Rails development environment configuration file (config/environment/development.rb):

config.webpacker.check_yarn_integrity = false

You may also turn on this feature by adding the config option to any Rails environment configuration file:

config.webpacker.check_yarn_integrity = true

Integrations

Webpacker ships with basic out-of-the-box integration for React, Angular, Vue and Elm. You can see a list of available commands/tasks by running bundle exec rails webpacker:

React

To use Webpacker with React, create a new Rails 5.1+ app using --webpack=react option:

# Rails 5.1+
rails new myapp --webpack=react

(or run bundle exec rails webpacker:install:react in a existing Rails app already setup with Webpacker).

The installer will add all relevant dependencies using Yarn, changes to the configuration files, and an example React component to your project in app/javascript/packs so that you can experiment with React right away.

Angular with TypeScript

To use Webpacker with Angular, create a new Rails 5.1+ app using --webpack=angular option:

# Rails 5.1+
rails new myapp --webpack=angular

(or run bundle exec rails webpacker:install:angular on a Rails app already setup with Webpacker).

The installer will add the TypeScript and Angular core libraries using Yarn alongside a few changes to the configuration files. An example component written in TypeScript will also be added to your project in app/javascript so that you can experiment with Angular right away.

By default, Angular uses a JIT compiler for development environment. This compiler is not compatible with restrictive CSP (Content Security Policy) environments like Rails 5.2+. You can use Angular AOT compiler in development with the @ngtools/webpack plugin.

Alternatively if you're using Rails 5.2+ you can enable unsafe-eval rule for your development environment. This can be done in the config/initializers/content_security_policy.rb with the following code:

  if Rails.env.development?
    policy.script_src :self, :https, :unsafe_eval
  else
    policy.script_src :self, :https
  end

Vue

To use Webpacker with Vue, create a new Rails 5.1+ app using --webpack=vue option:

# Rails 5.1+
rails new myapp --webpack=vue

(or run bundle exec rails webpacker:install:vue on a Rails app already setup with Webpacker).

The installer will add Vue and its required libraries using Yarn alongside automatically applying changes needed to the configuration files. An example component will be added to your project in app/javascript so that you can experiment with Vue right away.

If you're using Rails 5.2+ you'll need to enable unsafe-eval rule for your development environment. This can be done in the config/initializers/content_security_policy.rb with the following configuration:

  if Rails.env.development?
    policy.script_src :self, :https, :unsafe_eval
  else
    policy.script_src :self, :https
  end

You can read more about this in the Vue docs.

Elm

To use Webpacker with Elm, create a new Rails 5.1+ app using --webpack=elm option:

# Rails 5.1+
rails new myapp --webpack=elm

(or run bundle exec rails webpacker:install:elm on a Rails app already setup with Webpacker).

The Elm library and its core packages will be added via Yarn and Elm. An example Main.elm app will also be added to your project in app/javascript so that you can experiment with Elm right away.

Stimulus

To use Webpacker with Stimulus, create a new Rails 5.1+ app using --webpack=stimulus option:

# Rails 5.1+
rails new myapp --webpack=stimulus

(or run bundle exec rails webpacker:install:stimulus on a Rails app already setup with Webpacker).

Please read The Stimulus Handbook or learn more about its source code at https://github.com/stimulusjs/stimulus

Coffeescript

To add Coffeescript support, run bundle exec rails webpacker:install:coffee on a Rails app already setup with Webpacker.

An example hello_coffee.coffee file will also be added to your project in app/javascript/packs so that you can experiment with Coffeescript right away.

Erb

To add Erb support in your JS templates, run bundle exec rails webpacker:install:erb on a Rails app already setup with Webpacker.

An example hello_erb.js.erb file will also be added to your project in app/javascript/packs so that you can experiment with Erb-flavoured javascript right away.

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/javascript/packs/*(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/javascript.

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

# config/webpacker.yml
source_path: frontend
source_entry_path: 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.

Resolved

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 resolved_paths option available in config/webpacker.yml. This lets you add additional paths that webpack should lookup when resolving modules:

resolved_paths: ['app/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

Watched

By default, the lazy compilation is cached until a file is changed under your tracked paths. You can configure which paths are tracked by adding new paths to watched_paths array. This is much like Rails' autoload_paths:

# config/initializers/webpacker.rb
# or config/application.rb
Webpacker::Compiler.watched_paths << 'bower_components'

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).

Docs

You can find more detailed guides under docs.

License

Webpacker is released under the MIT License.