React scoped CSS

CSS encapsulation solution for React

Why

In order to solve the problem of css encapsulation, there are two main approaches, css-modules and css-in-js. However, both of them have a very very big problem. The developer experience is not good, by which I mean you often have to write more code than you expect to achieve a simple style. With react-scoped-css, you can just write the normal css you know, while having the advantage of css encapsulation!

How does it work

Write your css in a file ends with .scoped.css (scss & sass are also supported)

/* Title.scoped.css */
.title {
  background: #999;
}

p {
  color: #ddd;
}

Import the css file

// Title.jsx
import React from 'react'
import './Title.scoped.css'

const Title = props => {
  return (
    <h1 className="title">
      <p>{props.children}</p>
    </h1>
  )
}

export default Title

Then, in the html, component with scoped css file imported has a unique data-v-<hash> attribute on the html element tag, and the css selector also has a corresponding hash like selector[data-v-<hash>]. So all the styles in Title.scoped.css are scoped to Title.jsx. The output will be something like the following.

<h1 class="title" data-v-15763057=""><p data-v-15763057="">React scoped CSS</p></h1>

.title[data-v-15763057] {
  background: #309dcf;
}
p[data-v-15763057] {
  color: #fff;
}

How to use

Use in an existing create-react-app project (which hasn't been ejected yet)

Since create-react-app doesn't allow you to change webpack and babel config. So in this scenario, you have to use craco to override webpack config. Luckily you don't have to do it manually, I created a craco plugin that can do it for you.

Setup craco following this guide

Then, install craco-plugin-scoped-css

yarn add craco-plugin-scoped-css

create a craco.config.js in your project root

module.exports = {
  plugins: [
    {
      plugin: require('craco-plugin-scoped-css'),
    },
  ],
}

Manual setup

You have to add one babel plugin and one webpack loader.

the babel plugin

yarn add babel-plugin-react-scoped-css --dev

and in your babelrc add

"plugins": ["babel-plugin-react-scoped-css"]

also note that you can define your own matching rule like this

"plugins": [
  [
    "babel-plugin-react-scoped-css",
    {
      "include": ".local.(sa|sc|c)ss$"
    }
  ]
]

If you have other plugins installed, just add it to the list, order doesn't matter.

Plugin options:

• include(optional, RegExp, defaults to /\.scoped\.(sa|sc|c)ss$/): config which css file to be identified as scoped
• hashSeed (optional, string): used to calculate attribute hash. (TODO: a better explanation)

the webpack loader

yarn add scoped-css-loader --dev

and in your webpack.config.js

{
  test: /\.(sc|c|sa)ss$/,
  use: [
    {
      loader: 'style-loader',
    },
    {
      loader: 'css-loader',
      options: {
        sourceMap: true,
        importLoaders: 2,
      },
    },
    // You have to put it after `css-loader` and before any `pre-precessing loader`
    { loader: 'scoped-css-loader' },
    {
      loader: 'sass-loader',
    },
  ],
},

That's it for the configuration.

About the deep selector

If you want to affect the child components, you can use the deep selector.

.parent /deep/ .child {
  ...
}

This will be converted to

.parent[data-v-15760357] .child {
  ...
}

This method might be useful when you want to override the styles of the external libraries.

However, in the recent implementation of sass (dart-sass), /deep/ is not supported. You can use ::v-deep instead. (related issue)

.parent::v-deep .child {
  ...
}

When you want to use that, make sure that the version of @vue/component-compiler-utils installed in your project's node_modules is >= 2.6.0.

Examples

• webpack example
• create react app example

Common errors

Fragment : Invalid prop data-v-xxxxxxxx supplied to React.Fragment

react-scoped-css won't add data-v attribute to <></> or <React.Fragment></React.Fragment>. But it won't know for sure that <Fragment> is a react fragment and assigned data-v- to it (related issue)

Invalid code

import React, { Fragment } from 'react'

export function MyComponent() {
  return (
    <Fragment>
      ...
    </Fragment>
  )
}

Valid code

import React from 'react'

export function MyComponent() {
  return (
    <>
      ...
    </>
  )
}

import React from 'react'

export function MyComponent() {
  return (
    <React.Fragment>
      ...
    </React.Fragment>
  )
}