Webpacker makes it easy to use the JavaScript pre-processor 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).
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.
- Prerequisites
- Features
- Installation
- Integrations
- Binstubs
- Developing with Webpacker
- Configuration
- Linking Styles, Images and Fonts
- How-tos
- Extending
- Deployment
- Testing
- Troubleshooting
- Wishlist
- License
- Ruby 2.2+
- Rails 4.2+
- Node.js 6.4.0+
- Yarn 0.20.1+
- Webpack 2
- 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
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
, run bundle and ./bin/rails webpacker:install
or
bundle exec rake webpacker:install
(on rails version < 5.0):
# 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
Webpacker 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:
# Within rails app
./bin/rails webpacker
or in rails version < 5.0
# Within rails app
./bin/rake webpacker
To use Webpacker with React, create a
new Rails 5.1+ app using --webpack=react
option:
# 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.
To use Webpacker with Angular, create a
new Rails 5.1+ app using --webpack=angular
option:
# 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.
To use Webpacker with Vue, create a
new Rails 5.1+ app using --webpack=vue
option:
# 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.
Rails helpers cannot be used in .vue
files by default. To enable them, change
the extension to .vue.erb
and additionally amend the test
in
config/webpack/loaders/vue.js
to also include .vue.erb
files:
# config/webpack/loaders/vue.js
module.exports = {
test: /\.vue(\.erb)?$/,
...
}
To use Webpacker with Elm, 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.
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.
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. That means you don't have to run any separate process. Compilation errors are logged to the standard Rails log.
If you want to use live code reloading, you'll need to run ./bin/webpack-dev-server
in a separate terminal from ./bin/rails server
. This process will watch for changes
in the app/javascript/packs/*.js
files and automatically reload the browser to match.
Note: The dev server serves pack files from http://localhost:8080/
by default, which
is a different origin than your application server. Therefore it's not compatible with
things like Service Workers, that requires you to serve from the same origin.
If you'd rather not have to run the two processes separately by hand, you can use Foreman:
gem install foreman
# Procfile
web: bundle exec rails s
webpacker: ./bin/webpack-dev-server
foreman start
By default, webpack-dev-server
listens on 0.0.0.0
that means listening
on all IP addresses available on your system: LAN IP address, localhost, 127.0.0.1 etc.
However, we use localhost
as default hostname for serving assets in browser
and if you want to change that, for example on cloud9 you can do so
by changing host set in config/webpacker.yml
.
dev_server:
host: example.com
You can also pass CLI options supported by webpack-dev-server. Please note that inline options will always take precedence over the ones already set in the configuration file.
./bin/webpack-dev-server --host example.com --inline true --hot false
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.
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:
module.exports = {
test: /\.json$/,
use: 'json-loader'
}
Finally add .json
to the list of extensions in config/webpacker.yml
. Now if you import()
any .json
files inside your javascript
they will be processed using json-loader
. Voila!
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:
# 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:
# config/webpacker.yml
development:
dev_server:
host: 0.0.0.0
port: 8080
https: false
hot_reloading: false
If you have hot_reloading 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.
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 then you can use resolved_paths
option available in config/webpacker.yml
, which lets you
add additional paths webpack should lookup when resolving modules:
resolved_paths: ['app/assets']
You can then import them 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
Webpacker ships with babel - 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.
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 that includes a custom regenerator runtime and core-js.
Webpacker out-of-the-box provides CSS post-processing using
postcss-loader
and the installer sets up a standard .postcssrc.yml
file in your app root with standard plugins.
plugins:
postcss-smart-import: {}
postcss-cssnext: {}
Webpacker out-of-the-box provides CDN support using your Rails app config.action_controller.asset_host
setting. If you already have CDN added in your rails app
you don't need to do anything extra for webpacker, it just works.
If you're using the webpack-dev-server
in development, you can serve views over HTTPS
by setting 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.
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/
If you are using hot reloading, you should either set the dev_server/hot_reloading
key to TRUE or set the
ENV value WEBPACKER_HMR=TRUE
. That way, your stylesheet pack tag will do nothing because you
need your styles inlined in your JavaScript for hot reloading to work properly.
Live Reloading is having your assets for development provided by the webpack-dev-server.
You can override the the presence of the dev_server
setup by setting ENV value: WEBPACKER_DEV_SERVER=FALSE
.
You might do this if you are switching back and forth between statically compiling files during development and trying to get hot reloading to work.
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.
// app/javascript/hello_react/styles/hello-react.sass
.hello-react
padding: 20px
font-size: 12px
// 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'
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 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.
<%= 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 <link rel="prefetch">
or <img />
for an asset.
<%= asset_pack_path 'hello_react.css' %>
<%# => "/packs/hello_react.css" %>
<img src="<%= asset_pack_path 'calendar.png' %>" />
<% # => <img src="/packs/calendar.png" /> %>
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
:
// app/javascript/app-styles.sass
// ~ to tell webpack that this is not a relative import:
@import '~@material/animation/mdc-animation'
@import '~bootstrap/dist/css/bootstrap'
// Your main app pack
// app/javascript/packs/app.js
import '../app-styles'
<%# In your views %>
<%= javascript_pack_tag 'app' %>
<%= stylesheet_pack_tag 'app' %>
Let's say you're building a calendar app. Your JS app structure could look like this:
// 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
<%# app/views/layouts/application.html.erb %>
<%= javascript_pack_tag 'calendar' %>
<%= stylesheet_pack_tag 'calendar' %>
But it could also look a million other ways.
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' %>
If you need more advanced React-integration, like server rendering, redux, or react-router, see shakacode/react_on_rails, react-rails, and webpacker-react.
If you're not concerned with view helpers to pass props or server rendering, can do it yourself:
<%# views/layouts/application.html.erb %>
<%= content_tag :div,
id: "hello-react",
data: {
message: 'Hello!',
name: 'David'
}.to_json do %>
<% end %>
// app/javascript/packs/hello_react.js
const Hello = props => (
<div className='react-app-wrapper'>
<img src={clockIcon} alt="clock" />
<h5 className='hello-react'>
{props.message} {props.name}!
</h5>
</div>
)
// Render component with data
document.addEventListener('DOMContentLoaded', () => {
const node = document.getElementById('hello-react')
const data = JSON.parse(node.getAttribute('data'))
ReactDOM.render(<Hello {...data} />, node)
})
<%= content_tag :div,
id: "hello-vue",
data: {
message: "Hello!",
name: "David"
}.to_json do %>
<% end %>
<div id="hello-vue" data-name="David" data-message="Hello!"></div>
// Render component with props
document.addEventListener('DOMContentLoaded', () => {
const node = document.getElementById('hello-vue')
const props = JSON.parse(node.getAttribute('data'))
new Vue({
render: h => h(App, { props })
}).$mount('#hello-vue');
})
You can follow same steps for Angular too.
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:
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.
// 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
:
<%# Head %>
<%= javascript_pack_tag 'manifest' %>
<%= javascript_pack_tag 'vendor' %>
<%# If importing any styles from node_modules in your JS app %>
<%= stylesheet_pack_tag 'vendor' %>
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.
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
export const foo = () => console.log('hello world')
import { foo } from './foo'
To add any new JS module you can use yarn
:
yarn add bootstrap material-ui
You can use yarn to add bootstrap or any other modules available on npm:
yarn add bootstrap
Import Bootstrap and theme(optional) CSS in your app/javascript/packs/app.js file:
import 'bootstrap/dist/css/bootstrap'
import 'bootstrap/dist/css/bootstrap-theme'
Or in your app/javascript/app.sass file:
// ~ to tell that this is not a relative import
@import '~bootstrap/dist/css/bootstrap'
@import '~bootstrap/dist/css/bootstrap-theme'
- Setup react using webpacker react installer. Then add required depedencies for using typescript with React:
yarn add ts-loader typescript @types/react @types/react-dom
# You don't need this with typescript
yarn remove prop-types
- Add a
tsconfig.json
to project root:
{
"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
}
- Add a new loader
config/webpack/loaders/typescript.js
:
module.exports = {
test: /.(ts|tsx)$/,
loader: 'ts-loader'
}
- Finally add
.tsx
to the list of extensions inconfig/webpacker.yml
and rename your generatedhello_react.js
using react installer tohello_react.tsx
and make it valid typescript and now you can use typescript, JSX with React.
After you have installed angular using angular installer you would need to follow these steps to add HTML templates support:
- Use
yarn
to add html-loader
yarn add html-loader
- Add html-loader to
config/webpacker/loaders/html.js
module.exports = {
test: /\.html$/,
use: [{
loader: 'html-loader',
options: {
minimize: true,
removeAttributeQuotes: false,
caseSensitive: true,
customAttrSurround: [ [/#/, /(?:)/], [/\*/, /(?:)/], [/\[?\(?/, /(?:)/] ],
customAttrAssign: [ /\)?\]?=/ ]
}
}]
}
- Add
.html
toconfig/webpacker.yml
extensions:
- .elm
- .coffee
- .html
- Setup a custom
d.ts
definition
// app/javascript/hello_angular/html.d.ts
declare module "*.html" {
const content: string
export default content
}
- Add a template.html file relative to
app.component.ts
<h1>Hello {{name}}</h1>
- Import template into
app.component.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!
To enable CSS modules, you would need to update config/webpack/loaders/sass.js
file, particularly css-loader
:
// 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:
import React from 'react'
import styles from './styles'
const Hello = props => (
<div className={styles.wrapper}>
<img src={clockIcon} alt="clock" className={styles.img} />
<h5 className={styles.name}>
{props.message} {props.name}!
</h5>
</div>
)
css-next is supported out-of-box in Webpacker allowing the use of latest CSS features, today.
If you are using vim or emacs and want to ignore certain files you can add ignore-loader
:
yarn add ignore-loader
and create a new loader file inside config/webpack/loaders
:
// config/webpack/loaders/ignores.js
// ignores vue~ swap files
module.exports = {
test: /.vue~$/,
loader: 'ignore-loader'
}
And now all files with .vue~
will be ignored by the webpack compiler.
It's possible to link to assets that have been precompiled by sprockets. Add the .erb
extension to your javascript file, then you can use Sprockets' asset helpers:
<%# app/javascript/my_pack/example.js.erb %>
<% helpers = ActionController::Base.helpers %>
var railsImagePath = "<%= helpers.image_path('rails.png') %>"
This is enabled by the rails-erb-loader
loader rule in config/webpack/loaders/erb.js
.
You can also use babel-plugin-module-resolver to reference assets directly from app/assets/**
yarn add babel-plugin-module-resolver
Specify the plugin in your .babelrc
with the custom root or alias. Here's an example:
{
"plugins": [
["module-resolver", {
"root": ["./app"],
"alias": {
"assets": "./assets"
}
}]
]
}
And then within your javascript app code:
// Note: we don't have do any ../../ jazz
import FooImage from 'assets/images/foo-image.png'
import 'assets/stylesheets/bar'
Environment variables are supported out of the box in Webpacker. For example if you run the Webpack dev server like so:
FOO=hello BAR=world ./bin/webpack-dev-server
You can then reference these variables in your javascript app code with
process.env
:
console.log(process.env.FOO) // Compiles to console.log("hello")
You may want to store configuration in environment variables via .env
files,
similar to the dotenv Ruby gem.
In development, if you use Foreman or Invoker
to launch the Webpack server, both of these tools have basic support for a
.env
file (Invoker also supports .env.local
), so no further configuration
is needed.
However, if you run the Webpack server without Foreman/Invoker, or if you
want more control over what .env
files to load, you can use the
dotenv npm package. Here is what you could
do to support a "Ruby-like" dotenv:
yarn add dotenv
// config/webpack/shared.js
...
const dotenv = require('dotenv');
const dotenvFiles = [
`.env.${process.env.NODE_ENV}.local`,
'.env.local',
`.env.${process.env.NODE_ENV}`,
'.env'
];
dotenvFiles.forEach((dotenvFile) => {
dotenv.config({ path: dotenvFile, silent: true });
});
module.exports = {
...
Warning: using Foreman/Invoker and npm dotenv at the same time can result in confusing behavior, in that Foreman/Invoker variables take precedence over npm dotenv variables.
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:
module.exports = {
production: {
plugins: [
// ... Add plugins
]
},
development: {
output: {
// ... Custom output path
}
}
}
// config/webpack/production.js
const { plugins } = require('./app-config.js')
plugins: appConfig.plugins.concat([
// ...existing plugins
])
But this could be done million other ways.
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:
<!-- In development mode -->
<script src="/packs/calendar.js"></script>
<link rel="stylesheet" media="screen" href="/packs/calendar.css">
<!-- 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 production mode -->
<script src="/packs/calendar-0bd141f6d9360cf4a7f5.js"></script>
<link rel="stylesheet" media="screen" href="/packs/calendar-dc02976b5f94b507e3b6.css">
Heroku installs yarn and node by default if you deploy a rails app with Webpacker so all you would need to do:
heroku create shiny-webpacker-app
heroku addons:create heroku-postgresql:hobby-dev
git push heroku master
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:
// Example react component
import React from 'react'
import ReactDOM from 'react-dom'
import PropTypes from 'prop-types'
const Hello = props => (
<div>Hello David</div>
)
document.addEventListener('DOMContentLoaded', () => {
ReactDOM.render(
<Hello />,
document.body.appendChild(document.createElement('div')),
)
})
<%# views/pages/home.html.erb %>
<%= javascript_pack_tag "hello_react" %>
# 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
By default, the lazy compilation is cached until a file is changed under
tracked paths. You can configure the paths tracked
by adding new paths to watched_paths
array, much like rails autoload_paths
:
# config/initializers/webpacker.rb
# or config/application.rb
Webpacker::Compiler.watched_paths << 'bower_components'
Compiler stores a timestamp under tmp/webpacker/
directory to keep track of
changes and you can configure that by overriding compiler cache_dir
:
Webpacker::Compiler.cache_dir = "tmp/foo"
- If you get this error
ENOENT: no such file or directory - node-sass
on Heroku or elsewhere duringassets:precompile
orbundle exec rails webpacker:compile
then you would need to rebuild node-sass. It's a bit of a weird error; basically, it can't find thenode-sass
binary. An easy solution is to create a postinstall hook -npm rebuild node-sass
inpackage.json
and that will ensurenode-sass
is rebuilt 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 amanifest.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.
- Do you have any process running on port 8080? Since only one process can occupy each port, you can change the port number of webpack-dev-server at
config/webpacker.yml
under dev_server's port. Alternatively, you can stop the process from occupying port 8080. To do so, simply find the process id (PID) usinglsof -i :8080
and kill the process with its PID usingkill -9 PID
.
- If you get this error while trying to use Elm, try rebuilding Elm. You can do
so with a postinstall hook in your
package.json
:
"scripts": {
"postinstall": "npm rebuild elm"
}
-
This could happen if
webpacker:install
step is skipped. Please runbundle exec rails webpacker:install
to fix the issue. -
If you encounter the above error on heroku after upgrading from Rails 4.x to 5.1.x, then the problem might be related to missing
yarn
binstub. Please run following commands to update/add binstubs:
bundle config --delete bin
./bin/rails app:update:bin # or rails app:update:bin
If you are running Webpack on Windows, your command shell may not be able to interpret the preferred interpreter
for the scripts generated in bin/webpack
and bin/webpack-dev-server
. Instead you'll want to run the scripts
manually with Ruby:
C:\path>ruby bin\webpack
C:\path>ruby bin\webpack-dev-server
Webpacker is released under the MIT License.