css.md

CSS, Sass and SCSS

Webpacker supports importing CSS, Sass and SCSS files directly into your JavaScript files.

Importing and loading styles is a two step process:

1. You need to tell webpack which file(s) it has to compile and know how to load

   When you do import '../scss/application.scss', you're telling webpack to include application.scss in the build. This does not mean it's going to be compiled into your javascript, only that webpack now compiles and knows how to load this file. (How that file compilation is handled is depending on how your loaders (css-loader, sass-loader, file-loader, etc.) are configured.)

2. You need to load those files in your views

   In order to have styles load in production, you need to include stylesheet_pack_tag with the same name as the javascript file that imports the styles.

   When you do <%= stylesheet_pack_tag 'application' %>, that's a run-time inclusion from Rails, where Rails gets the correct "asset path" to that file from webpack.

Import global styles into your JS app

// app/javascript/hello_react/styles/hello-react.sass

.hello-react
  padding: 20px
  font-size: 12px

// React component example
// app/javascript/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>
)

Import scoped styles into your JS app

Stylesheets that end with .module.* are treated as CSS Modules.

// app/javascript/hello_react/styles/hello-react.module.sass

.helloReact
  padding: 20px
  font-size: 12px

// React component example
// app/javascript/packs/hello_react.jsx

import React from 'react'
import helloIcon from '../hello_react/images/icon.png'
import styles from '../hello_react/styles/hello-react'

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

Note: Declared class is referenced as object property in JavaScript.

Import scoped styles into your TypeScript app

Using CSS modules with a TypeScript application requires a few differences from a JavaScript app. The CSS / Sass files are the same:

// app/javascript/hello_react/styles/hello-react.module.sass

.helloReact
  padding: 20px
  font-size: 12px

There must also be a type definition file for these styles:

export const helloReact: string;

You can then import the styles like this:

// React component example
// app/javascripts/packs/hello_react.tsx

import React from 'react'
import helloIcon from '../hello_react/images/icon.png'
import * as styles from '../hello_react/styles/hello-react.module.sass'

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

You can automatically generate type definitions for the styles by installing the typed-scss-modules as a development dependency:

yarn add typed-scss-modules --dev

Then by adding these lines to your package.json:

"scripts": {
  "gen-typings": "yarn run tsm app/javascript/**/*.sass",
  "watch-typings": "yarn run tsm app/javascript/**/*.sass -w"
},

You can generate the typings for the stylesheet by running the command yarn gen-typings when you've finished writing CSS, or run yarn watch-typings to have it automatically generate them as you go.

Link styles from your Rails views

Under the hood webpack uses mini-css-extract-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' %>

Webpacker emits css files only if extract_css is set to true in webpacker.yml otherwise stylesheet_pack_tag returns nil.

Add bootstrap

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'

Post-Processing CSS

Webpacker out-of-the-box provides CSS post-processing using postcss-loader and the installer sets up a standard postcss.config.js file in your app root with standard plugins.

module.exports = {
  plugins: [
    require('postcss-import'),
    require('postcss-flexbugs-fixes'),
    require('postcss-preset-env')({
      autoprefixer: {
        flexbox: 'no-2009'
      },
      stage: 3
    })
  ]
}

Using CSS with vue-loader

Vue templates require loading the stylesheet in your application in order for CSS to work. This is in addition to loading the JavaScript file for the entry point. Loading the stylesheet will also load the CSS for any nested components.

<%= stylesheet_pack_tag 'hello_vue' %>
<%= javascript_pack_tag 'hello_vue' %>

Resolve url loader

Since Sass/libsass does not provide url rewriting, all linked assets must be relative to the output. Add the missing url rewriting using the resolve-url-loader. Place it directly after the sass-loader in the loader chain.

yarn add resolve-url-loader

// webpack/environment.js
const { environment } = require('@rails/webpacker')

// resolve-url-loader must be used before sass-loader
environment.loaders.get('sass').use.splice(-1, 0, {
  loader: 'resolve-url-loader'
});

module.exports = environment

Working with TypeScript

In order to get CSS to work with typescript you have two options. You can either use require to bypass typescript special import.

const styles = require('../hello_react/styles/hello-react');

You may also use the package typings-for-css-modules-loader instead of css-loader to automatically generate typescript .d.ts files in order to help resolve any css/scss styles. To do that:

// app/javascript/packs/hello_react.jsx
import * as styles from '../hello_react.styles/hello-react.module.scss';

yarn add --dev typings-for-css-modules-loader

// webpack/environment.js
const { environment } = require('@rails/webpacker')

// replace css-loader with typings-for-css-modules-loader
environment.loaders.get('moduleSass').use = environment.loaders.get('moduleSass').use.map((u) => {
  if(u.loader == 'css-loader') {
    return { ...u, loader: 'typings-for-css-modules-loader' };
  } else {
    return u;
  }
});