jxl-in-css

v0.1.0

Published

3 years ago

PostCSS plugin to use JXL in CSS background

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jxl jpeg-xl background css image polyfill postcss postcss-plugin

JPEG XL in CSS

PostCSS plugin and tiny JS script (150B) to useJPEG XL in CSS background

With this PostCSS Plugin you can use JPEG XL image format in your CSS background in Supported Browsers, and fallback with the original image.

How works?

You add require('jxl-in-css') to your JS bundle and write CSS like:

.logo {
  width: 80px;
  height: 80px;
  background-image: url(logo.jpg);
}

The script will set jxl or no-jxl class on <body> and PostCSS plugin will generate:

.logo {
  width: 80px;
  height: 80px;
}
body.jxl .logo {
  background-image: url(logo.jxl);
}
body.no-jxl .logo {
  background-image: url(logo.jpg);
}

Usage

1. Convert to JXL

Convert you images to jxl format, you can use Squoosh

2. Install `jxl-in-css`

npm install --save-dev jxl-in-css

2.1 Load the polyfill

Add the JS script to your client-side JS bundle:

// CommonJS
+ require('jxl-in-css/polyfill.js')

// ES6
+ import 'jxl-in-css/polyfill.js'

Since JS script is very small (315B gzipped), the best way for landings is to inline it to HTML:

+   <script><%= readFile('node_modules/jxl-in-css') %></script>
  </head>

You can load the script via CDN:

+   <script src="https://unpkg.com/jxl-in-css/polyfill.js"></script>
  </head>

2.2 Load the PostCSS plugin

Check do you use PostCSS already in your bundler. You can check postcss.config.js in the project root, "postcss" section in package.json or postcss in bundle config.

If you don’t have it already, add PostCSS to your bundle:

For webpack see postcss-loader docs.
For Parcel create postcss.config.js file. It already has PostCSS support.

Add `jxl-in-css` to PostCSS plugins

module.exports = {
  plugins: [
+   require('jxl-in-css'),
    require('autoprefixer')
  ]
}

If you use CSS Modules in webpack add modules: true option:

module.exports = {
  plugins: [
-   require(jxl-in-css'),
+   require(jxl-in-css')({ modules: true }),
    require('autoprefixer')
  ]
}

PostCSS Options

module.exports = {
  plugins: [
    require('jxl-in-css')({ /* options */ }),
  ]
}

| Option | Description | Default Value | Type Value | | ------ | ----------- | ------------- | ---------- | | modules | Wrap classes to :global() to support CSS Modules. | false | Boolean | | jxlClass | Class name for browser with jxl support. | jxl | String | | noJxlClass | Class name for browser without jxl support. | no-jxl | String | | rename | Get a new file name from old name, like (oldName: string) => string, then url(./image.png) → url(./image.png.jxl). | | Function |

Supported browsers

Chrome Canary 92+ with Enabled JXL image format chrome://flags/#enable-jxl

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