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Description

Use Webpack to manage app-like JavaScript modules in Rails

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Webpacker

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node.js Gem

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 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 10.17.0+ || 12+ || 14+
  • Yarn 1.x+

Features

  • webpack 4.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', '~> 5.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

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:
  ├── packs:
  │   # only webpack entry files here
  │   └── application.js
  │   └── application.css
  └── src:
  │   └── my_component.js
  └── stylesheets:
  │   └── my_styles.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
:

If you want to link a static asset for

 or 
tag, you can use the
asset_pack_path
helper:

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.


Important: Pass all your pack names when using

javascript_packs_with_chunks_tag
helper otherwise you will get duplicated chunks on the page.

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_
. 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

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:
  <<: 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>

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

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
rails webpacker:install
yarn upgrade @rails/webpacker --latest
yarn upgrade webpack-dev-server --latest

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

yarn add @rails/[email protected]

Integrations

Webpacker ships with basic out-of-the-box integration. You can see a list of available commands/tasks by running

bundle exec rails webpacker
.

Included install integrations:

See Integrations for further details.

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

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.

Docs

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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