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Description

Use Webpack to manage app-like JavaScript modules in Rails

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Webpacker

Ruby specs Jest specs Rubocop JS lint

node.js Gem

Webpacker makes it easy to use the JavaScript pre-processor and bundler Webpack v5 to 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

  • 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
:

The

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

The result looks like this:



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.




If you want to link a static asset for

tag, you can use the
asset_pack_path
helper:
erb

Or use the dedicated helper:

erb

'2x' } %>

If you want to create a favicon:

erb

If you want to preload a static asset in your

, you can use the 
preload_pack_asset
helper:
erb

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_
. 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 base
config/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 and then 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
:
bash
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: ```js // 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:
  <<: production depends on precompilation of packs prior to booting for performance. compile: false cache manifest.json performance cache_manifest: true compile staging 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/[email protected] yarn up [email protected]

Or to install the latest release (including pre-releases)

yarn add @rails/[email protected]

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 you add 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

Code Helpers

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

License

Webpacker is released under the MIT License.

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