css-custom-globals-loader

Exposes CSS globals like custom properties, custom media queries and custom selectors.

Recommended with postcss-preset-env, instructions below.

Usage

yarn add css-custom-globals-loader

Basic

Make sure to include it before css-loader:

// webpack.config.js
module.exports = {
  // ...
  module: {
    rules: [
      {
        test: /\.css$/,
        use: [
          'style-loader',
          'css-custom-globals-loader',
          'css-loader',
        ],
      },
    ],
  },
}

Write CSS containing globals:

/* style.css */
:root {
  --primary-color: lightblue;
}
 
@custom-media --narrow-window (max-width: 30em);
 
@custom-selector :--title h1;

Import them into JavaScript:

// index.js
import { customProperties, customMedia, customSelectors } from './style.css'
 
console.log(customProperties['--primary-color']) // 'lightblue'
console.log(customMedia['--narrow-window']) // '(max-width: 30em)'
console.log(customSelectors['--title']) // 'h1'

With CSS Modules

When using CSS Modules, CSS globals will be exported along with class names in the same object.

// webpack.config.js
module.exports = {
  // ...
  module: {
    rules: [
      {
        test: /\.css$/,
        use: [
          'style-loader',
          'css-custom-globals-loader',
          'css-loader?modules',
        ],
      },
    ],
  },
}

/* style.css */
:root {
  --primary-color: lightblue;
}
 
.link {
  color: var(--primary-color);
}

// index.js
import styles from './style.css'
 
console.log(styles.customProperties['--primary-color']) // 'lightblue'
console.log(styles.link) // '_23_aKvs-b8bW2Vg3fwHozO'

With CSS Modules and postcss-preset-env

yarn add postcss-loader postcss-preset-env

// webpack.config.js
module.exports = {
  // ...
  module: {
    rules: [
      {
        test: /\.css$/,
        use: [
          'style-loader',
          'css-custom-globals-loader',
          'css-loader?modules&importLoaders=1',
          'postcss-loader',
        ]
      },
    ],
  },
}

Configure postcss-preset-env to use globals when compiling CSS files:

// postcss.config.js
module.exports = {
  plugins: {
    'postcss-preset-env': {
      // contents of this file will be available in every CSS file
      importFrom: 'globals.css',
      // enable all features, the default stage 2
      // doesn't include features like custom media queries
      stage: 0,
      // don't strip off experimental features like custom media queries,
      // otherwise css-custom-globals-loader won't be able to expose them
      preserve: true,
    },
  },
}

/* globals.css */
@custom-media --narrow-window (min-width: 30em);
 
:root {
  --image-width: 300px;
  --image-width-narrow: 200px;
}

Now this custom media query and custom properties will be available in all CSS files:

/* style.css */
.image {
  width: var(--image-width);
}
 
@media (--narrow-window) {
  .image {
    width: var(--image-width-narrow);
  }
}

// index.js
import React from 'react'
import { customMedia, customProperties } from './globals.css'
import styles from './style.css'
 
const Image = () => (
  <img
    className={styles.image}
    alt="a kitten"
    src="kitten-200.jpg"
    srcSet="kitten-200.jpg 200w,
            kitten-300.jpg 300w"
    sizes={`
      ${customMedia['--narrow-window']} ${customProperties['--image-width-narrow']},
      ${customProperties['--image-width']}
    `}
  />
)

Always import your globals. Even if you're not sharing CSS globals with JavaScript, import globals.css at least once in your app in order to ensure that its contents end up in your CSS. It's true that postcss-preset-env provides fallbacks for browsers that don't support custom properties, but those that do will try to use them and fail if they don't exist.

Despite its name, importFrom doesn't actually import that file, postcss-preset-env only uses it to provide fallbacks. This is why you need to import it as a module yourself.

Caveats

Exposing globals and class names in the same object is not ideal because if we were to use the class name .customProperties, it would get overwritten with the customProperties object and we would be unable to access it.