@rails/webpacker
Advanced tools
@rails/webpacker is a gem that integrates Webpack with Ruby on Rails, allowing you to use modern JavaScript tooling and libraries in your Rails application. It provides a standard way to manage JavaScript, CSS, and other assets in a Rails project.
JavaScript Bundling
Webpacker allows you to bundle JavaScript files. The configuration specifies the entry point and the output location for the bundled file.
module.exports = {
entry: './app/javascript/packs/application.js',
output: {
filename: 'bundle.js',
path: __dirname + '/public/packs'
}
};CSS and Asset Management
You can manage CSS and other assets like images and fonts. This example shows how to import a custom stylesheet and a Bootstrap CSS file.
import '../stylesheets/application';
import 'bootstrap/dist/css/bootstrap';Hot Module Replacement
Webpacker supports Hot Module Replacement (HMR) for a better development experience. This configuration enables HMR and sets the content base directory.
module.exports = {
devServer: {
hot: true,
contentBase: './public/packs'
}
};Integration with Rails
Webpacker integrates seamlessly with Rails views. You can use helper methods to include JavaScript and CSS packs in your Rails templates.
<%= javascript_pack_tag 'application' %>
<%= stylesheet_pack_tag 'application' %>Webpack is a module bundler for JavaScript applications. It is highly configurable and can be used independently of any framework. Unlike @rails/webpacker, it does not provide Rails-specific integrations out of the box.
Parcel is a web application bundler that requires zero configuration. It is simpler to set up compared to Webpack and @rails/webpacker, but it may not offer the same level of customization and Rails-specific features.
Vite is a build tool that aims to provide a faster and leaner development experience for modern web projects. It offers a similar feature set to Webpack but focuses on speed and simplicity. Vite can be integrated with Rails, but it requires additional configuration.
Webpacker makes it easy to use the JavaScript pre-processor and bundler webpack 4.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.
NOTE: The master branch now hosts the code for v4.x.x. Please refer to 3-x-stable branch for 3.x documentation. See the v4-upgrade guide for an overview of the changes.
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', '~> 4.x'
# OR if you prefer to use master
gem 'webpacker', git: 'https://github.com/rails/webpacker.git'
yarn add https://github.com/rails/webpacker.git
yarn add core-js regenerator-runtime
Finally, run the following to install Webpacker:
bundle
bundle exec rails webpacker:install
# OR (on rails version < 5.0)
bundle exec rake webpacker:install
Optional: To fix "unmet peer dependency" warnings,
yarn upgrade
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
In /packs/application.js, include this at the top of the file:
import "core-js/stable";
import "regenerator-runtime/runtime";
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' %>" />
If you are using new webpack 4 split chunks API, then consider using javascript_packs_with_chunks_tag helper, which creates html
tags for a pack and all the dependent chunks.
<%= javascript_packs_with_chunks_tag 'calendar', 'map', 'data-turbolinks-track': 'reload' %>
<script src="/packs/vendor-16838bab065ae1e314.js" data-turbolinks-track="reload"></script>
<script src="/packs/calendar~runtime-16838bab065ae1e314.js" data-turbolinks-track="reload"></script>
<script src="/packs/calendar-1016838bab065ae1e314.js" data-turbolinks-track="reload"></script>
<script src="/packs/map~runtime-16838bab065ae1e314.js" data-turbolinks-track="reload"></script>
<script src="/packs/map-16838bab065ae1e314.js" data-turbolinks-track="reload"></script>
Important: Pass all your pack names when using javascript_packs_with_chunks_tag
helper otherwise you will get duplicated chunks on the page.
<%# DO %>
<%= javascript_packs_with_chunks_tag 'calendar', 'map' %>
<%# DON'T %>
<%= javascript_packs_with_chunks_tag 'calendar' %>
<%= javascript_packs_with_chunks_tag 'map' %>
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.
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:
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
See docs/webpack for modifying webpack configuration and loaders.
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, 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
./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
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
rails webpacker:binstubs
yarn upgrade @rails/webpacker --latest
yarn upgrade webpack-dev-server --latest
# Or to install the latest release (including pre-releases)
yarn add @rails/webpacker@next
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 change the default setting in config/webpacker.yml:
# config/webpacker.yml
development:
...
# Verifies that correct packages and versions are installed by inspecting package.json, yarn.lock, and node_modules
check_yarn_integrity: false
You may also turn on this feature by adding the config option for any Rails environment in config/webpacker.yml:
check_yarn_integrity: true
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:
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 an 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.
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:
Rails.application.config.content_security_policy do |policy|
if Rails.env.development?
policy.script_src :self, :https, :unsafe_eval
else
policy.script_src :self, :https
end
end
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:
Rails.application.config.content_security_policy do |policy|
if Rails.env.development?
policy.script_src :self, :https, :unsafe_eval
else
policy.script_src :self, :https
end
end
You can read more about this in the Vue docs.
See docs/es6 to know more about Webpack and Webpacker configuration.
For instance, you can lazy load Vue JS components:
Before:
import Vue from 'vue'
import { VCard } from 'vuetify/lib'
Vue.component('VCard', VCard)
After:
import Vue from 'vue'
// With destructuring assignment
Vue.component('VCard', import('vuetify/lib').then(({ VCard }) => VCard)
// Or without destructuring assignment
Vue.component('OtherComponent', () => import('./OtherComponent'))
You can use it in a Single File Component as well:
<template>
...
</template>
<script>
export default {
components: {
OtherComponent: () => import('./OtherComponent')
}
}
</script>
By wrapping the import function into an arrow function, Vue will execute it only when it gets requested, loading the module in that moment.
/**
* The following block of code may be used to automatically register your
* Vue components. It will recursively scan this directory for the Vue
* components and automatically register them with their "basename".
*
* Eg. ./components/OtherComponent.vue -> <other-component></other-component>
* Eg. ./UI/ButtonComponent.vue -> <button-component></button-component>
*/
const files = require.context('./', true, /\.vue$/i)
files.keys().map(key => {
const component = key.split('/').pop().split('.')[0]
// With Lazy Loading
Vue.component(component, () => import(`${key}`))
// Or without Lazy Loading
Vue.component(component, files(key).default)
})
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.
To use Webpacker with Svelte, create a
new Rails 5.1+ app using --webpack=svelte option:
# Rails 5.1+
rails new myapp --webpack=svelte
(or run bundle exec rails webpacker:install:svelte on a Rails app already setup with Webpacker).
Please play with the Svelte Tutorial or learn more about its API at https://svelte.dev/docs
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
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.
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.
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.
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
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'
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).
We encourage you to contribute to Webpacker! See CONTRIBUTING for guidelines about how to proceed.
Webpacker is released under the MIT License.
[4.1.0] - 2019-11-12
FAQs
Use webpack to manage app-like JavaScript modules in Rails
The npm package @rails/webpacker receives a total of 299,069 weekly downloads. As such, @rails/webpacker popularity was classified as popular.
We found that @rails/webpacker demonstrated a not healthy version release cadence and project activity because the last version was released a year ago. It has 8 open source maintainers collaborating on the project.
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