# Webpacker
[](https://nodejs.org/en/)
[](https://github.com/rails/webpacker)
Webpacker makes it easy to use the JavaScript pre-processor and bundler
[Webpack 2.x.x+](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.
## Table of Contents
- [Prerequisites](#prerequisites)
- [Features](#features)
- [Installation](#installation)
- [Integrations](#integrations)
- [React](#react)
- [Angular with TypeScript](#angular-with-typescript)
- [Vue](#vue)
- [Elm](#elm)
- [Binstubs](#binstubs)
- [Webpack dev server](#webpack-dev-server)
- [Webpack](#webpack)
- [Configuration](#configuration)
- [Webpack](#webpack-1)
- [Loaders](#loaders)
- [Paths](#paths)
- [Babel](#babel)
- [Post-Processing CSS](#post-processing-css)
- [CDN](#cdn)
- [HTTPS in development](#https-in-development)
- [Hot module replacement](#hot-module-replacement)
- [Linking Styles, Images and Fonts](#linking-styles-images-and-fonts)
- [Within your JS app](#within-your-js-app)
- [Inside views](#inside-views)
- [From node modules folder](#from-node-modules-folder)
- [How-tos](#how-tos)
- [App structure](#app-structure)
- [Namespacing](#namespacing)
- [Pass data from view](#pass-data-from-view)
- [React](#react-1)
- [Vue](#vue-1)
- [Add common chunks](#add-common-chunks)
- [Module import() vs require()](#module-import-vs-require)
- [Add a new npm module](#add-a-new-npm-module)
- [Add bootstrap](#add-bootstrap)
- [Use Typescript with React](#use-typescript-with-react)
- [Use HTML templates with Typescript and Angular](#use-html-templates-with-typescript-and-angular)
- [CSS modules](#css-modules)
- [CSS-Next](#css-next)
- [Ignoring swap files](#ignoring-swap-files)
- [Link sprocket assets](#link-sprocket-assets)
- [Using helpers](#using-helpers)
- [Using babel module resolver](#using-babel-module-resolver)
- [Extending](#extending)
- [Deployment](#deployment)
- [Heroku](#heroku)
- [Testing](#testing)
- [Troubleshooting](#troubleshooting)
- [Wishlist](#wishlist)
- [License](#license)
## Prerequisites
* Ruby 2.2+
* Rails 4.2+
* Node.js 6.4.0+
* Yarn 0.20.1+
## Features
* [Webpack 2](https://webpack.js.org/)
* ES6 with [babel](https://babeljs.io/)
* 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:
```bash
# Available Rails 5.1+
rails new myapp --webpack
```
Or add it to your `Gemfile`, run bundle and `./bin/rails webpacker:install` or `bundle exec rake webpacker:install` (on rails version < 5.0):
```ruby
# Gemfile
gem 'webpacker', '~> 2.0'
# OR if you prefer to use master
gem 'webpacker', git: 'https://github.com/rails/webpacker.git'
```
**Note:** Use `rake` instead of `rails` if you are using webpacker
with rails version < 5.0
## Integrations
Webpacker by default 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:
```bash
# Within rails app
./bin/rails webpacker
```
or in rails version < 5.0
```bash
# Within rails app
./bin/rake webpacker
```
### React
To use Webpacker with [React](https://facebook.github.io/react/), create a
new Rails 5.1+ app using `--webpack=react` option:
```bash
# Rails 5.1+
rails new myapp --webpack=react
```
(or run `./bin/rails webpacker:install:react` in a existing Rails app already
setup with webpacker).
The installer will add all relevant dependencies using yarn, any 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.
### Angular with TypeScript
To use Webpacker with [Angular](https://angularjs.org/), create a
new Rails 5.1+ app using `--webpack=angular` option:
```bash
# Rails 5.1+
rails new myapp --webpack=angular
```
(or run `./bin/rails webpacker:install:angular` on a Rails app already
setup with webpacker).
The installer will add TypeScript and Angular core libraries using yarn plus
any changes to the configuration files. An example component is written in
TypeScript will also be added to your project in `app/javascript` so that
you can experiment with Angular right away.
### Vue
To use Webpacker with [Vue](https://vuejs.org/), create a
new Rails 5.1+ app using `--webpack=vue` option:
```bash
# Rails 5.1+
rails new myapp --webpack=vue
```
(or run `./bin/rails webpacker:install:vue` on a Rails app already setup with webpacker).
The installer will add Vue and required libraries using yarn plus
any changes to the configuration files. An example component will
also be added to your project in `app/javascript` so that you can
experiment Vue right away.
### Elm
To use Webpacker with [Elm](http://elm-lang.org), create a
new Rails 5.1+ app using `--webpack=elm` option:
```
# Rails 5.1+
rails new myapp --webpack=elm
```
(or run `./bin/rails webpacker:install:elm` on a Rails app already setup with webpacker).
The Elm library and core packages will be added via Yarn and Elm itself.
An example `Main.elm` app will also be added to your project in `app/javascript`
so that you can experiment with Elm right away.
## Binstubs
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`
executable to ensure that the right configuration file and environment variables
are loaded depending on your environment.
### Webpack dev server
In development, you'll need to run `./bin/webpack-dev-server` in a separate terminal
from `./bin/rails server` to have your `app/javascript/packs/*.js` files compiled
as you make changes.
`./bin/webpack-dev-server` launches the [Webpack Dev Server](https://webpack.js.org/configuration/dev-server/), which serves your pack files
on `http://localhost:8080/` by default and supports live code reloading in the development environment. You will need to install additional plugins for Webpack if you want
features like [Hot Module Replacement](https://webpack.js.org/guides/hmr-react/).
If you'd rather not have to run the two processes separately by hand, you can use [Foreman](https://ddollar.github.io/foreman):
```bash
gem install foreman
```
```yml
# Procfile
web: bundle exec rails s
webpacker: ./bin/webpack-dev-server
```
```bash
foreman start
```
You can also pass CLI options supported by [webpack-dev-server](https://webpack.js.org/configuration/dev-server/). Please note that inline options will always take
precedence over the ones already set in the configuration file.
```bash
./bin/webpack-dev-server --host 0.0.0.0 --inline true --hot false
```
### Webpack
We recommend using `webpack-dev-server` during development for a better experience,
however, if you don't want that for some reason you can always use `webpack` binstub with
watch option, which uses webpack Command Line Interface (CLI). This will use `public_output_path` from `config/webpacker.yml`
directory to serve your packs using configured rails server.
You can pass cli options available with [Webpack](https://webpack.js.org/api/cli/):
```bash
./bin/webpack --watch --progress --colors
```
## Configuration
### Webpack
Webpacker gives you a default set of configuration files for test, development and
production environments. They all live together with the shared
points in `config/webpack/*.js`.
By default, you shouldn't have 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.
### Loaders
Webpack enables the use of loaders to preprocess files. This allows you to
bundle any static resource way beyond JavaScript. All base loaders
that ships with webpacker are located inside `config/webpack/loaders`.
If you want to add a new loader, for example, to process `json` files via webpack:
```
yarn add json-loader
```
And create a `json.js` file inside `loaders` directory:
```js
module.exports = {
test: /\.json$/,
use: 'json-loader'
}
```
Now if you `import()` any `.json` files inside your javascript
they will be processed using `json-loader`. Voila!
### Paths
By default, webpacker ships with simple conventions for where the javascript
app files and compiled webpack bundles will go in your rails app,
but 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).
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:
```yml
# config/webpacker.yml
source_path: frontend
source_entry_path: packs
public_output_path: assets/packs # outputs to => public/assets/packs
```
Similary you can also control and configure `webpack-dev-server` settings from `config/webpacker.yml` file:
```yml
# config/webpacker.yml
development:
dev_server:
host: 0.0.0.0
port: 8080
https: false
```
### Babel
Webpacker ships with [babel](https://babeljs.io/) - a JavaScript compiler so
you can use next generation JavaScript, today. The Webpacker installer sets up a
standard `.babelrc` file in your app root, which will work great in most cases
because of [babel-env-preset](https://github.com/babel/babel-preset-env).
Following ES6/7 features are supported out of the box:
* Async/await.
* Object Rest/Spread Properties.
* Exponentiation Operator.
* Dynamic import() - useful for route level code-splitting
* Class Fields and Static Properties.
We have also included [babel polyfill](https://babeljs.io/docs/usage/polyfill/)
that includes a custom regenerator runtime and core-js.
### Post-Processing CSS
Webpacker out-of-the-box provides CSS post-processing using
[postcss-loader](https://github.com/postcss/postcss-loader)
and the installer sets up a standard `.postcssrc.yml`
file in your app root with standard plugins.
```yml
plugins:
postcss-smart-import: {}
postcss-cssnext: {}
```
### CDN
Webpacker out-of-the-box provides CDN support using your Rails app `config.action_controller.asset_host` setting. If you already have [CDN](http://guides.rubyonrails.org/asset_pipeline.html#cdns) added in your rails app
you don't need to do anything extra for webpacker, it just works.
### HTTPS in development
You may require the `webpack-dev-server` to serve views over HTTPS in development.
To do this, set the `https` option for `webpack-dev-server`
to `true` in `config/webpacker.yml`, then start the dev server as usual
with `./bin/webpack-dev-server`.
Please note that the `webpack-dev-server` will use a self-signed certificate,
so your web browser will display a warning upon accessing the page.
### Hot module replacement
Webpacker out-of-the-box doesn't ship with HMR just yet. You will need to
install additional plugins for Webpack if you want to add HMR support.
You can checkout these links on this subject:
- https://webpack.js.org/configuration/dev-server/#devserver-hot
- https://webpack.js.org/guides/hmr-react/
## Linking Styles, Images and Fonts
Static assets like images, fonts and stylesheets support is enabled out-of-box
and you can link them into your javascript app code and have them
compiled automatically.
### Within your JS app
```sass
// app/javascript/hello_react/styles/hello-react.sass
.hello-react
padding: 20px
font-size: 12px
```
```js
// React component example
// app/javascripts/packs/hello_react.jsx
import React from 'react'
import helloIcon from '../hello_react/images/icon.png'
import '../hello_react/styles/hello-react.sass'
const Hello = props => (
Hello {props.name}!
)
```
### Inside views
Under the hood webpack uses
[extract-text-webpack-plugin](https://github.com/webpack-contrib/extract-text-webpack-plugin) plugin to extract all the referenced styles within your app and compile it into
a separate `[pack_name].css` bundle so that in your view you can use the
`stylesheet_pack_tag` helper.
```erb
<%= stylesheet_pack_tag 'hello_react' %>
```
You can also link js/images/styles used within your js app in views using
`asset_pack_path` helper. This helper is useful in cases where you just want to
create a `` or `` for an asset.
```erb
<%= asset_pack_path 'hello_react.css' %>
<%# => "/packs/hello_react.css" %>
<% # => %>
```
### From node modules folder
You can also import styles from `node_modules` using the following syntax.
Please note that your styles will always be extracted into `[pack_name].css`:
```sass
// app/javascript/app-styles.sass
// ~ to tell webpack that this is not a relative import:
@import '~@material/animation/mdc-animation.scss'
@import '~boostrap/dist/bootstrap.css'
```
```js
// Your main app pack
// app/javascript/packs/app.js
import '../app-styles'
```
```erb
<%# In your views %>
<%= javascript_pack_tag 'app' %>
<%= stylesheet_pack_tag 'app' %>
```
## How-tos
### App structure
Let's say you're building a calendar app. Your JS app structure could look like this:
```js
// app/javascript/packs/calendar.js
import 'calendar'
```
```
app/javascript/calendar/index.js // gets loaded by import 'calendar'
app/javascript/calendar/components/grid.jsx
app/javascript/calendar/styles/grid.sass
app/javascript/calendar/models/month.js
```
```erb
<%# app/views/layouts/application.html.erb %>
<%= javascript_pack_tag 'calendar' %>
<%= stylesheet_pack_tag 'calendar' %>
```
But it could also look a million other ways.
#### Namespacing
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:
```erb
<%# app/views/admin/orders/index.html.erb %>
<%= javascript_pack_tag 'admin/orders' %>
```
and
```erb
<%# app/views/shop/orders/index.html.erb %>
<%= javascript_pack_tag 'shop/orders' %>
```
### Pass data from view
#### React
You may consider using [react-rails](https://github.com/reactjs/react-rails) or
[webpacker-react](https://github.com/renchap/webpacker-react) for more advanced react integration. However here is how you can do it yourself:
```erb
<%# views/layouts/application.html.erb %>
<%= content_tag :div,
id: "hello-react",
data: {
message: 'Hello!',
name: 'David'
}.to_json do %>
<% end %>
```
```js
// app/javascript/packs/hello_react.js
const Hello = props => (
{props.message} {props.name}!
)
// Render component with data
document.addEventListener('DOMContentLoaded', () => {
const node = document.getElementById('hello-react')
const data = JSON.parse(node.getAttribute('data'))
ReactDOM.render(, node)
})
```
#### Vue
```erb
<%= content_tag :div,
id: "hello-vue",
data: {
message: "Hello!",
name: "David"
} do %>
<% end %>
```
```html
```
```js
// Render component with data
document.addEventListener('DOMContentLoaded', () => {
const node = document.getElementById('hello-vue')
const data = JSON.parse(node.getAttribute('data'))
const app = new Vue({
data: data,
el: '#vue-app',
template: '',
components: { App }
})
console.log(app)
})
```
You can follow same steps for Angular too.
### Add common chunks
The CommonsChunkPlugin is an opt-in feature that creates a separate file (known as a chunk), consisting of common modules shared between multiple entry points. By separating common modules from bundles, the resulting chunked file can be loaded once initially, and stored in the cache for later use. This results in page speed optimizations as the browser can quickly serve the shared code from the cache, rather than being forced to load a larger bundle whenever a new page is visited.
Create a `app-config.js` file inside `config/webpack` and in that file add:
```js
module.exports = {
plugins: [
// Creates a common vendor.js with all shared modules
new webpack.optimize.CommonsChunkPlugin({
name: 'vendor',
minChunks: (module) => {
// this assumes your vendor imports exist in the node_modules directory
return module.context && module.context.indexOf('node_modules') !== -1;
}
}),
// Webpack code chunk - manifest.js
new webpack.optimize.CommonsChunkPlugin({
name: 'manifest',
minChunks: Infinity
})
]
}
```
You can add this in `shared.js` too but we are doing this to ensure smoother upgrades.
```js
// config/webpack/shared.js
// .... rest of the config
const appConfig = require('./app-config.js')
plugins: appConfig.plugins.concat([
// ...existing plugins
])
```
Now, add these files to your `layouts/application.html.erb`:
```erb
<%# Head %>
<%= javascript_pack_tag 'manifest' %>
<%= javascript_pack_tag 'vendor' %>
<%# If importing any styles from node_modules in your JS app %>
<%= stylesheet_pack_tag 'vendor' %>
```
### Module import() vs require()
While you are free to use `require()` and `module.exports`, we encourage you
to use `import` and `export` instead since it reads and looks much better.
```js
import Button from 'react-bootstrap/lib/Button'
// or
import { Button } from 'react-bootstrap'
class Foo {
// code...
}
export default Foo
import Foo from './foo'
```
You can also use named export and import
```js
export const foo = () => console.log('hello world')
import { foo } from './foo'
```
### Add a new npm module
To add any new JS module you can use `yarn`:
```bash
yarn add bootstrap material-ui
```
### Add bootstrap
You can use yarn to add bootstrap or any other modules available on npm:
```bash
yarn add bootstrap
```
Import Bootstrap and theme(optional) CSS in your app/javascript/packs/app.js file:
```js
import 'bootstrap/dist/css/bootstrap.css'
import 'bootstrap/dist/css/bootstrap-theme.css'
```
Or in your app/javascript/app.sass file:
```sass
// ~ to tell that this is not a relative import
@import '~bootstrap/dist/css/bootstrap.css'
@import '~bootstrap/dist/css/bootstrap-theme.css'
```
### Use Typescript with React
1. Setup react using webpacker [react installer](#react). Then add required depedencies
for using typescript with React:
```bash
yarn add ts-loader typescript @types/react @types/react-dom
# You don't need this with typescript
yarn remove prop-types
```
2. Add a `tsconfig.json` to project root:
``` json
{
"compilerOptions": {
"declaration": false,
"emitDecoratorMetadata": true,
"experimentalDecorators": true,
"lib": ["es6", "dom"],
"module": "es6",
"moduleResolution": "node",
"sourceMap": true,
"jsx": "react",
"target": "es5"
},
"exclude": [
"**/*.spec.ts",
"node_modules",
"public"
],
"compileOnSave": false
}
```
3. Add a new loader `config/webpack/loaders/typescript.js`:
``` js
module.exports = {
test: /.(ts|tsx)$/,
loader: 'ts-loader'
}
```
4. Finally add `.tsx` to the list of extensions in `config/webpacker.yml`
and rename your generated `hello_react.js` using react installer
to `hello_react.tsx` and make it valid typescript and now you can use
typescript, JSX with React.
### Use HTML templates with Typescript and Angular
After you have installed angular using [angular installer](#angular-with-typescript)
you would need to follow these steps to add HTML templates support:
1. Use `yarn` to add html-loader
```bash
yarn add html-loader
```
2. Add html-loader to `config/webpacker/loaders/html.js`
```js
module.exports = {
test: /\.html$/,
use: [{
loader: 'html-loader',
options: {
minimize: true,
removeAttributeQuotes: false,
caseSensitive: true,
customAttrSurround: [ [/#/, /(?:)/], [/\*/, /(?:)/], [/\[?\(?/, /(?:)/] ],
customAttrAssign: [ /\)?\]?=/ ]
}
}]
}
```
3. Add `.html` to `config/webpacker.yml`
```yml
extensions:
- .elm
- .coffee
- .html
```
4. Setup a custom `d.ts` definition
```ts
// app/javascript/hello_angular/html.d.ts
declare module "*.html" {
const content: string
export default content
}
```
5. Add a template.html file relative to `app.component.ts`
```html
Hello {{name}}
```
6. Import template into `app.component.ts`
```ts
import { Component } from '@angular/core'
import templateString from './template.html'
@Component({
selector: 'hello-angular',
template: templateString
})
export class AppComponent {
name = 'Angular!'
}
```
That's all. Voila!
### CSS modules
To enable CSS modules, you would need to update `config/webpack/loaders/sass.js`
file, particularly `css-loader`:
```js
// Add css-modules
{
loader: 'css-loader',
options: {
minimize: env.NODE_ENV === 'production',
modules: true,
localIdentName: '[path][name]__[local]--[hash:base64:5]'
}
}
```
That's all. Now, you can use CSS modules within your JS app:
```js
import React from 'react'
import styles from './styles.css'
const Hello = props => (
{props.message} {props.name}!
)
```
### CSS-Next
[css-next](http://cssnext.io/) is supported out-of-box in Webpacker allowing the use of
latest CSS features, today.
### Ignoring swap files
If you are using vim or emacs and want to ignore certain files you can add `ignore-loader`:
```
yard add ignore-loader
```
and create a new loader file inside `config/webpack/loaders`:
```js
// config/webpack/loaders/ignores.js
// ignores vue~ swap files
module.exports = {
test: /.vue~$/,
loader: 'ignore-loader'
}
```
And now all files with `.vue~` will be ignored by the webpack compiler.
### Link sprocket assets
#### Using helpers
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:
```erb
<%# 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/loaders/erb.js`.
#### Using babel module resolver
You can also use [babel-plugin-module-resolver](https://github.com/tleunen/babel-plugin-module-resolver) to reference assets directly from `app/assets/**`
```bash
yarn add babel-plugin-module-resolver
```
Specify the plugin in your `.babelrc` with the custom root or alias. Here's an example:
```json
{
"plugins": [
["module-resolver", {
"root": ["./app"],
"alias": {
"assets": "./assets"
}
}]
]
}
```
And then within your javascript app code:
```js
// Note: we don't have do any ../../ jazz
import FooImage from 'assets/images/foo-image.png'
import 'assets/stylesheets/bar.sass'
```
## Extending
We suggest you don't directly overwrite the provided configuration files
and extend instead for smoother upgrades. Here is one way to do it:
Create a `app-config.js` file inside `config/webpack`, and in that add:
```js
module.exports = {
production: {
plugins: [
// ... Add plugins
]
},
development: {
output: {
// ... Custom output path
}
}
}
```
```js
// config/webpack/production.js
const { plugins } = require('./app-config.js')
plugins: appConfig.plugins.concat([
// ...existing plugins
])
```
But this could be done million other ways.
## 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 you
can manually trigger `bundle exec rails webpacker:compile` during your app deploy.
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:
```html
```
### Heroku
Heroku installs yarn and node by default if you deploy a rails app with
Webpacker so all you would need to do:
```bash
heroku create shiny-webpacker-app
heroku addons:create heroku-postgresql:hobby-dev
git push heroku master
```
## Testing
Webpacker lazily compiles assets in test env so you can write your tests without any extra
setup and everything will just work out of the box.
Here is a sample system test case with hello_react example component:
```js
// Example react component
import React from 'react'
import ReactDOM from 'react-dom'
import PropTypes from 'prop-types'
const Hello = props => (
Hello David
)
document.addEventListener('DOMContentLoaded', () => {
ReactDOM.render(
,
document.body.appendChild(document.createElement('div')),
)
})
```
```erb
<%# views/pages/home.html.erb %>
<%= javascript_pack_tag "hello_react" %>
```
```rb
# Tests example react component
require "application_system_test_case"
class HomesTest < ApplicationSystemTestCase
test "can see the hello message" do
visit root_url
assert_selector "h5", text: "Hello! David"
end
end
```
## 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 the 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-dev-server`) is running and has
completed the compilation successfully before loading a view.
## Wishlist
- HMR - [#188](https://github.com/rails/webpacker/issues/188)
- Support rails engines - [#348](https://github.com/rails/webpacker/issues/348)
## License
Webpacker is released under the [MIT License](https://opensource.org/licenses/MIT).
<% # => 
%>
```
### From node modules folder
You can also import styles from `node_modules` using the following syntax.
Please note that your styles will always be extracted into `[pack_name].css`:
```sass
// app/javascript/app-styles.sass
// ~ to tell webpack that this is not a relative import:
@import '~@material/animation/mdc-animation.scss'
@import '~boostrap/dist/bootstrap.css'
```
```js
// Your main app pack
// app/javascript/packs/app.js
import '../app-styles'
```
```erb
<%# In your views %>
<%= javascript_pack_tag 'app' %>
<%= stylesheet_pack_tag 'app' %>
```
## How-tos
### App structure
Let's say you're building a calendar app. Your JS app structure could look like this:
```js
// app/javascript/packs/calendar.js
import 'calendar'
```
```
app/javascript/calendar/index.js // gets loaded by import 'calendar'
app/javascript/calendar/components/grid.jsx
app/javascript/calendar/styles/grid.sass
app/javascript/calendar/models/month.js
```
```erb
<%# app/views/layouts/application.html.erb %>
<%= javascript_pack_tag 'calendar' %>
<%= stylesheet_pack_tag 'calendar' %>
```
But it could also look a million other ways.
#### Namespacing
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:
```erb
<%# app/views/admin/orders/index.html.erb %>
<%= javascript_pack_tag 'admin/orders' %>
```
and
```erb
<%# app/views/shop/orders/index.html.erb %>
<%= javascript_pack_tag 'shop/orders' %>
```
### Pass data from view
#### React
You may consider using [react-rails](https://github.com/reactjs/react-rails) or
[webpacker-react](https://github.com/renchap/webpacker-react) for more advanced react integration. However here is how you can do it yourself:
```erb
<%# views/layouts/application.html.erb %>
<%= content_tag :div,
id: "hello-react",
data: {
message: 'Hello!',
name: 'David'
}.to_json do %>
<% end %>
```
```js
// app/javascript/packs/hello_react.js
const Hello = props => (