Serves as an alternative and also addition to postcss-loader. While webpack loaders are pretty efficient, they allow you to process just one file at time.

This plugin tries to solve this issue while taking great inspiration from postcss-pipeline-webpack-plugin. It allows you to run PostCSS plugins on generated (and newly emitted) assets, with support for webpack 5.x filesystem cache and ability to change content of existing assets, rather than a need to always generate new ones.

Installation

npm i -D postcss-webpack-plugin

Usage

// webpack.config.js
const { PostCSSWebpackPlugin } = require('postcss-webpack-plugin');

module.exports = {
  entry: 'base.css',
  plugins: [
    new MiniCssExtractPlugin({
      filename: '[name].css',
      chunkFilename: '[id].[name].css',
    }),
    ...(config?.plugins ?? []),
  ],
  module: {
    rules: [
      {
        test: /.css$/i,
        use: [MiniCssExtractPlugin.loader, 'css-loader'],
      },
    ],
  },
  plugins: [
    new PostCSSWebpackPlugin({
      plugins: [require('postcss-pxtorem'), require('cssnano')],
    }),
  ],
};

Chaining multiple instances together

Following example first runs css nano and pxtorem plugin son the base.css asset and then creates a new one with only mobile styles (using unmq plugin) in the second pass.

// webpack.config.js
const { PostCSSWebpackPlugin } = require('postcss-webpack-plugin');

module.exports = {
  // ...
  plugins: [
    new PostCSSWebpackPlugin({
      plugins: [require('postcss-pxtorem'), require('cssnano')],
    }),
    new PostCSSWebpackPlugin({
      plugins: [
        require('postcss-unmq')({
          type: 'screen',
          width: 540,
        }),
      ],
      filename: '[name].mobile[ext]',
    })
  ]
}

Plugin options

interface PostCSSWebpackPluginOptions {
  filename?: string | ((filename: string) => string);
  filter?: RegExp | ((filename: string) => boolean);
  implementation?: Postcss;
  additionalAssets?: true | undefined;
  stage?: number;
  plugins: any[];
}

filename

string | ((filename: string) => string)

Optional custom filename. If not provided the plugins are applied on the existing css assets without creating new ones. Can be either function or string with support for [base], [dir], [ext], [name], [root] template variables.

filter

RegExp | ((filename: string) => boolean)

Custom function or RegExp to filter assets to process (defaults to /\.css$/).

implementation

Postcss

Optional custom implementation for postcss. Can be usefull in some projects where the default require('postcss') resolves to wrong version.

additionalAssets

true | undefined

Set to true to run plugin for newly emitted assets. Should be used in combination with filter option in order to prevent cycles in compilation.

stage

number

Custom plugin processAssets hook stage (defaults to PROCESS_ASSETS_STAGE_OPTIMIZE).

plugins

any[]

Array of postcss plugins.

Supported versions

• node 14+
• postcss 8+
• webpack 5+