Webpacker

Webpacker makes it easy to use the JavaScript preprocessor and bundler Webpack 2.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). It is, however, possible to use Webpacker for CSS and images 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.

It's designed to work with Rails 5.1+ and makes use of the Yarn dependency management that's been made default from that version forward.

Prerequisites

• Ruby 2.2+
• Rails 4.2+
• Node.js 6.4.0+
• Yarn

Installation

Webpacker is currently compatible with Rails 4.2+, but there's no guarantee it will still be in the future.

You can either make use of Webpacker during setup of a new application with --webpack or you can add the gem and run ./bin/rails webpacker:install in an existing application.

As the rubygems version isn't promised to be kept up to date until the release of Rails 5.1, you may want to include the gem directly from GitHub:

gem 'webpacker', github: 'rails/webpacker'

You can also see a list of available commands by running ./bin/rails webpacker

Binstubs

Webpacker ships with three binstubs: ./bin/webpack, ./bin/webpack-watcher and ./bin/webpack-dev-server. They're thin wrappers around the standard webpack.js executable, just to ensure that the right configuration file is loaded.

A binstub is also created to install your npm dependencies, and can be called via ./bin/yarn.

In development, you'll need to run either ./bin/webpack-dev-server or ./bin/webpack-watcher in a separate terminal from ./bin/rails server to have your app/javascript/packs/*.js files compiled as you make changes. If you'd rather not have to run the two processes separately by hand, you can use Foreman. ./bin/webpack-dev-server launches the Webpack Dev Server, which serves your pack files on http://localhost:8080/, and provides advanced Webpack features, such as Hot Module Replacement.

If you would rather forego the advanced features and serve your javascript packs directly from the rails server, you may use ./bin/webpack-watcher instead, but make sure to disable the Dev Server in config/webpack/development.server.yml, otherwise script tags will keep pointing to localhost:8080 and won't load properly.

Configuration

Webpacker gives you a default set of configuration files for development and production. They all live together with the shared points in config/webpack/*.js. By default, you shouldn't have to make any changes for a basic setup out the box. But this is where you do go if you need something more advanced.

The configuration for what Webpack is supposed to compile by default rests on the convention that every file in app/javascript/packs/* should be turned into their own output files (or entry points, as Webpack calls it).

Let's say you're building a calendar. Your structure could look like this:

// app/javascript/packs/calendar.js
require('calendar')

app/javascript/calendar/index.js // gets loaded by require('calendar')
app/javascript/calendar/components/grid.jsx
app/javascript/calendar/styles/grid.sass
app/javascript/calendar/models/month.js

<%# app/views/layouts/application.html.erb %>
<%= javascript_pack_tag 'calendar' %>
<%= stylesheet_pack_tag 'calendar' %>

But it could also look a million other ways.

Note: You can also namespace your packs using directories, similar to a Rails app.

app/javascript/packs/admin/orders.js
app/javascript/packs/shop/orders.js

and reference them in your views like this:

<%# app/views/admin/orders/index.html.erb %>
<%= javascript_pack_tag 'admin/orders' %>

and

<%# app/views/shop/orders/index.html.erb %>
<%= javascript_pack_tag 'shop/orders' %>

Advanced Configuration

By default, webpacker offers simple conventions for where the webpack configs, javascript app files and compiled webpack bundles will go in your rails app, but all these options are configurable from config/webpack/paths.yml file.

# config/webpack/paths.yml
source: app/javascript
entry: packs
output: public
config: config/webpack
node_modules: node_modules

Note: Behind the scenes, webpacker will use same entry directory name inside output directory to emit bundles. For ex, public/packs

Similary, you can also control and configure webpack-dev-server settings from config/webpack/development.server.yml file

# config/webpack/development.server.yml
enabled: true
host: localhost
port: 8080

By default, webpack-dev-server uses output option specified in paths.yml as contentBase.

Note: Don't forget to disable webpack-dev-server in case you are using ./bin/webpack-watcher to serve assets in development mode otherwise you will get 404 for assets because the helper tag will use webpack-dev-server url to serve assets instead of public directory.

Linking to static assets

Static assets like images, fonts and stylesheets support is enabled out-of-box so, you can link them into your javascript app code and have them compiled automatically.

// React component example
// app/javascripts/packs/hello_react.jsx
import React from 'react'
import ReactDOM from 'react-dom'
import helloIcon from '../hello_react/images/icon.png'
import '../hello_react/styles/hello-react.sass'

const Hello = props => (
  <div className="hello-react">
    <img src={helloIcon} alt="hello-icon" />
    <p>Hello {props.name}!</p>
  </div>
)

under the hood webpack uses extract-text-webpack-plugin plugin to extract all the referenced styles and compile it into a separate [pack_name].css bundle so that within your view you can use the stylesheet_pack_tag helper,

<%= stylesheet_pack_tag 'hello_react' %>

Getting asset path

Webpacker provides asset_pack_path helper to get the path of any given asset that's been compiled by webpack.

For ex, if you want to create a <link rel="prefetch"> or <img /> for an asset used in your pack code you can reference them like this in your view,

<%= asset_pack_path 'hello_react.css' %>
<% # => "/packs/hello_react.css" %>
<img src="<%= asset_pack_path 'calendar.png' %>" />
<% # => <img src="/packs/calendar.png" /> %>

Deployment

Webpacker hooks up a new webpacker:compile task to assets:precompile, which gets run whenever you run assets:precompile. The javascript_pack_tag and stylesheet_pack_tag helper method will automatically insert the correct HTML tag for compiled pack. Just like the asset pipeline does it. By default the output will look like this in different environments,

  <!-- In development mode with webpack-dev-server -->
  <script src="http://localhost:8080/calendar.js"></script>
  <link rel="stylesheet" media="screen" href="http://localhost:8080/calendar.css">
  <!-- In development mode -->
  <script src="/packs/calendar.js"></script>
  <link rel="stylesheet" media="screen" href="/packs/calendar.css">
  <!-- In production mode -->
  <script src="/packs/calendar-0bd141f6d9360cf4a7f5.js"></script>
  <link rel="stylesheet" media="screen" href="/packs/calendar-dc02976b5f94b507e3b6.css">

Linking to sprockets assets

It's possible to link to assets that have been precompiled by sprockets. Add the .erb extension to your javascript file, then you can use Sprockets' asset helpers:

// app/javascript/my_pack/example.js.erb

<% helpers = ActionController::Base.helpers %>
var railsImagePath = "<%= helpers.image_path('rails.png') %>";

This is enabled by the rails-erb-loader loader rule in config/webpack/shared.js.

Ready for React

To use Webpacker with React, just create a new app with rails new myapp --webpack=react (or run rails webpacker:install:react on a Rails app already setup with webpacker), and all the relevant dependencies will be added via yarn and changes to the configuration files made. Now you can create JSX files and have them properly compiled automatically.

Ready for Angular with TypeScript

To use Webpacker with Angular, just create a new app with rails new myapp --webpack=angular (or run rails webpacker:install:angular on a Rails app already setup with webpacker). TypeScript support and the Angular core libraries will be added via yarn and changes to the configuration files made. An example component written in TypeScript is also added to your project in app/javascript so that you can experiment Angular right away.

Ready for Vue

To use Webpacker with Vue, just create a new app with rails new myapp --webpack=vue (or run rails webpacker:install:vue on a Rails app already setup with webpacker). Vue and its supported libraries will be added via yarn and changes to the configuration files made. An example component is also added to your project in app/javascript so that you can experiment Vue right away.

Troubleshooting

• If you get this error ENOENT: no such file or directory - node-sass on Heroku or elsewhere during assets:precompile or bundle exec rails webpacker:compile then you would need to rebuild node-sass. It's a bit weird error, basically, it can't find the node-sass binary. An easy solution is to create a postinstall hook - npm rebuild node-sass in package.json and that will ensure node-sass is rebuild whenever you install any new modules.

• If you get this error Can't find hello_react.js in manifest.json when loading a view in browser it's because Webpack is still compiling packs. Webpacker uses a manifest.json file to keep track of packs in all environments, however since this file is generated after packs are compiled by webpack. So, if you load a view in browser whilst webpack is compiling you will get this error. Therefore, make sure webpack (i.e ./bin/webpack-watcher or ./bin/webpack-dev-server) is running and has completed the compilation successfully before loading a view.

Wishlist

• Improve process for linking to assets compiled by sprockets - shouldn't need to specify <% helpers = ActionController::Base.helpers %> at the beginning of each file
• Consider chunking setup

License

Webpacker is released under the MIT License.