# Webpacker

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Webpacker makes it easy to use the JavaScript pre-processor and bundler
[Webpack v5](https://webpack.js.org/)
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](https://github.com/rails/webpacker/tree/5-x-stable) branch for 5.x documentation.

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## Table of Contents

- [Prerequisites](#prerequisites)
- [Features](#features)
- [Installation](#installation)
  - [Usage](#usage)
  - [Development](#development)
  - [Webpack Configuration](#webpack-configuration)
  - [Custom Rails environments](#custom-rails-environments)
  - [Upgrading](#upgrading)
- [Paths](#paths)
  - [Resolved](#resolved)
  - [Watched](#watched)
- [Deployment](#deployment)
- [Contributing](#contributing)
- [License](#license)

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## Prerequisites

- Ruby 2.4+
- Rails 5.2+
- Node.js 10.22.1+ || 12+ || 14+
- Yarn 1.x+ || 2.x+

## Features

- [Webpack v5](https://webpack.js.org/)
- ES6 with [babel](https://babeljs.io/)
- 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 either add Webpacker during setup of a new Rails 5.1+ application
using new `--webpack` option:

```bash
# Available Rails 5.1+
rails new myapp --webpack
```

Or add it to your `Gemfile`:

```ruby
# Gemfile
gem 'webpacker', '~> 6.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
```

Finally, run the following to install Webpacker:

```bash
bundle
bundle exec rails webpacker:install

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

Optional: To fix ["unmet peer dependency" warnings](https://github.com/rails/webpacker/issues/1078),

```bash
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:

```bash
yarn install
```

### Usage

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

```yml
app/packs:
  ├── entrypoints:
  │   # 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`:

```erb
<%= javascript_pack_tag 'application' %>
<%= stylesheet_pack_tag 'application' %>
```

If you want to link a static asset for `<img />` tag, you can use the `asset_pack_path` helper:
```erb
<img src="<%= asset_pack_path 'images/logo.svg' %>" />
```

Or use the dedicated helper:
```erb
<%= image_pack_tag 'application.png', size: '16x10', alt: 'Edit Entry' %>
<%= image_pack_tag 'picture.png', srcset: { 'picture-2x.png' => '2x' } %>
```

If you want to create a favicon:
```erb
<%= favicon_pack_tag 'mb-icon.png', rel: 'apple-touch-icon', type: 'image/png' %>
```

If you want to preload a static asset in your `<head>`, you can use the `preload_pack_asset` helper:
```erb
<%= preload_pack_asset 'fonts/fa-regular-400.woff2' %>
```

If you want to use images in your stylesheets:

```css
.foo {
  background-image: url('../images/logo.svg')
}
```

Note, if you are using server-side rendering of JavaScript with dynamic code-spliting,
as is often done with extensions to Webpacker, like [React on Rails](https://github.com/shakacode/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 `app/packs/entrypoints/*.js` files and automatically
reload the browser to match. This feature is also known as
[Hot Module Replacement](https://webpack.js.org/concepts/hot-module-replacement/).

HMR is only the first step to running "Fast Refresh" with React. For more information
on how to configure rails/webpacker for Fast Refresh with React, see article
[HMR and React Hot Reloading](https://github.com/shakacode/react_on_rails/blob/master/docs/rails-webpacker-react-integration-options.md#hmr-and-react-hot-reloading).

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

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

# standalone build
./bin/webpack
```

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](https://webpack.js.org/configuration/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.

```bash
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:

```bash
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:

```ruby
  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.

```js
// 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`:

```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:

```js
// 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))
```

### 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:

#### CoffeeScript

```bash
yarn add coffeescript coffee-loader
```

#### TypeScript

```bash
yarn add typescript @babel/preset-typescript
```

Add tsconfig.json

```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
}
```

Babel won’t perform any type-checking on TypeScript code. To optionally use type-checking run:

```bash
yarn add fork-ts-checker-webpack-plugin
```

Then modify the webpack config to use it as a plugin:

```js
// 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:

```bash
yarn add css-loader mini-css-extract-plugin css-minimizer-webpack-plugin
```

optionally, add the css extension to webpack config for easy resolution.

```js
// 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

```bash
yarn add postcss-loader
```

#### Sass

```bash
yarn add sass sass-loader
```

#### Less

```bash
yarn add less less-loader
```

#### Stylus

```bash
yarn add stylus stylus-loader
```

#### React

React is supported and you just need to add relevant packages,

```bash
yarn add react react-dom @babel/preset-react
```

if you are using typescript, update your `tsconfig.json`

```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
}
```

For more information on React props hydration and Server-Side Rendering (SSR), see the article
[Rails/Webpacker React Integration Options](https://github.com/shakacode/react_on_rails/blob/master/docs/rails-webpacker-react-integration-options.md)
in the [ShakaCode/react_on_rails](https://github.com/shakacode/react_on_rails) repo.

#### Other frameworks

Please follow webpack integration guide for relevant framework or library,

1. [Svelte](https://github.com/sveltejs/svelte-loader#install)
2. [Angular](https://v2.angular.io/docs/ts/latest/guide/webpack.html#!#configure-webpack)
3. [Vue](https://vue-loader.vuejs.org/guide/)

For example to add Vue support:
```js
// config/webpack/rules/vue.js
const VueLoaderPlugin = require('vue-loader/lib/plugin')

module.exports = {
  module: {
    rules: [
      {
        test: /\.vue$/,
        loader: 'vue-loader'
      }
    ]
  },
  plugins: [new VueLoaderPlugin()]
}
```

```js
// config/webpack/base.js
const { webpackConfig, merge } = require('@rails/webpacker')
const vueConfig = require('./rules/vue')

module.exports = merge(webpackConfig, vueConfig)
```

### 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,

```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:

```bash
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

```bash
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.

```bash
# 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:

```bash
# 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 upgrade @rails/webpacker --latest
yarn upgrade webpack-dev-server --latest

# Or to install the latest release (including pre-releases)
yarn add @rails/webpacker@next
```

Also, consult the [CHANGELOG](./CHANGELOG.md) 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:

```yml
# 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:

```yml
# 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:

```yml
additional_paths: ['app/assets', 'vendor/assets']
```

You can then import these items inside your modules like so:

```js
// 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.

If you are using a CDN setup, webpacker will use the configured [asset host](https://guides.rubyonrails.org/configuring.html#rails-general-configuration) 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](./docs/troubleshooting.md).

## Contributing

[![Code Helpers](https://www.codetriage.com/rails/webpacker/badges/users.svg)](https://www.codetriage.com/rails/webpacker)

We encourage you to contribute to Webpacker! See [CONTRIBUTING](CONTRIBUTING.md) for guidelines about how to proceed.

## License

Webpacker is released under the [MIT License](https://opensource.org/licenses/MIT).