postcss-lightningcss

This PostCSS plugin uses lightningcss to compile and minify your CSS.

lightningcss is more than a minifier as it can replace quite a few PostCSS plugins such as autoprefixer. You can find the complete list of features in the package's documentation and the list of plugins it's able to replace below.

Install

yarn add -D postcss-lightningcss

Usage

const postcss = require("postcss");
const postcssLightningcss = require("postcss-lightningcss");

postcss([postcssLightningcss(/* pluginOptions */)]).process(
  YOUR_CSS /*, processOptions */
);

Options

const postcssLightningcss = require("postcss-lightningcss");

postcssLightningcss({
  // Use a browserslist query that will inform which browsers are supported
  // Will add or remove vendor prefixes that are needed or not anymore
  browsers: ">= .25%",
  // Auto set lightningcssOptions.cssModules, possible values:
  // - auto - enable CSS modules for all files matching `/\.module(s)?\.\w+$/i.test(filename)`
  // - RegExp - enable CSS modules for all files matching `/RegExp/i.test(filename)`
  // - boolean - true enable css modules for all files
  // Will be overwrite by the lightningcssOptions cssModules(boolean) option
  cssModules: /\.module\.css/,

  // Callback containing the transformed class names for cssModules
  // this runs only if cssModules is enabled
  cssModulesJSON(cssFileName: string, json: object, outputFileName: string): {},
  // Will pass all options to lightningcss
  // Check out their documentation for details:
  // https://www.npmjs.com/package/lightningcss#user-content-documentation
  lightningcssOptions: {
    // Enable minification (default: true)
    minify: true,

    // Enable source maps (default: true)
    sourceMap: true,

    // Compile as cssModules (default: undefined)
    cssModules: false,

    // For which browsers to compile (default: undefined)
    // Can be omitted if you set the `browsers` option
    targets: {
      safari: (13 << 16) | (2 << 8), // represents Safari 13.2.0
    },

    // Individually enable various drafts
    drafts: {
      // Enable css nesting (default: undefined)
      nesting: false,
    },
  },
});

The detailed list of lightningcssOptions can be found here

CSS Modules

When transforming CSS Modules, class names get changed, to get the mapping of the class names, you can specify a cssModulesJSON function like the following:

const path = require("path");
const fs = require("fs");

postcssLightningcss({
  cssModules: /\.module\.css/,
  cssModulesJSON(cssFileName, json, outputFileName) {
    const cssName = path.basename(cssFileName, ".css");
    const jsonFileName = path.resolve("./build/" + cssName + ".json");
    fs.writeFileSync(jsonFileName, JSON.stringify(json));
  },
});

You may also combine this with custom naming patterns:

postcssLightningcss({
  cssModulesJSON(cssFileName, json, outputFileName) {
    // Your export function here
  },
  lightningcssOptions: {
    cssModules: {
      pattern: "my-company-[name]-[hash]-[local]",
    },
  },
});

Note that using a custom pattern cannot be used at the same time as using a RegEx to conditionally enable cssModules because the cssModules option within lightningcssOptions takes precedence over the plugin's cssModules option

About source maps

Source maps will pass through lightningcss. But many mappings will be lost in translation; lightningcss creates only a source map for selectors. Mappings for properties cannot be re-created after this transformation.

PostCSS plugins that you can remove if you have lightningcss

This list is not exhaustive, if you have a doubt, have a look at the Lightning CSS Playground

The rows marked as "Depends on browser config" will convert your CSS only if:

1. You set the browsers or lightningcssOptions.targets options
2. one of the target browsers doesn't support the feature

PostCSS Plugin	lightningcss option
autoprefixer	Depends on browser config
postcss-clamp	Depends on browser config
postcss-color-hex-alpha	Depends on browser config
postcss-color-hsl	Depends on browser config
postcss-color-rgb	Depends on browser config
postcss-color-function	Depends on browser config
postcss-color-rebeccapurple	Depends on browser config
postcss-custom-media	lightningcssOptions.drafts.customMedia
postcss-double-position-gradients	Depends on browser config
postcss-hwb-function	Depends on browser config
postcss-lab-function	Depends on browser config
postcss-logical	Depends on browser config (1)
postcss-media-minmax	Depends on browser config
postcss-multi-value-display	Depends on browser config
postcss-nesting	lightningcssOptions.drafts.nesting
postcss-normalize-display-values	Depends on browser config
postcss-oklab-function	Depends on browser config
postcss-overflow-shorthand	Depends on browser config
postcss-place	Depends on browser config
postcss-progressive-custom-properties	Depends on browser config (2)

1. lightningcss doesn't support the logical shorthand keyword as its syntax is likely to change
2. Progressive custom properties works only if the properties don't contain properties themselves:

• lab(29.2345% 39.3825 20.0664) has a proper fallback
• oklch(40% 0.234 0.39 / var(--opacity-50)) will not have a fallback

License

MIT