Apply postcss plugins to webpack css asset

This webpack plugin gets css extracted by MiniCssExtractPlugin and applies postcss plugins to it.

Why?

If you use postcss-loader, not all its plugins are effective in file-by-file processing. For instance, css structural optimizations or media query packaging better apply to one css production file that can be generated by MiniCssExtractPlugin.

Installation

npm install --save-dev webpack postcss postcss-assets-webpack-plugin

Options

• test - regular expression for matching files returned from MiniCssExtractPlugin.
• plugins - array of postcss plugins
• log - boolean if plugin can print info to the console, true by default

Usage

Simple example of webpack config that tranforms css-modules with less and postcss. Autoprefixer is used in development and production, mqpacker and csswring are used only for production build.

import webpack from 'webpack';
import csswring from 'csswring';
import mqpacker from 'mqpacker';
import autoprefixer from 'autoprefixer';
import MiniCssExtractPlugin from 'mini-css-extract-plugin';
import PostCSSAssetsPlugin from 'postcss-assets-webpack-plugin';

const devMode = process.env.NODE_ENV !== 'production'

webpackConfig = {
  <...>
  postcss() {
    return [autoprefixer({browser: 'last 2 version', cascade: false})]
  },

  module: {
    rules: [
      {
        test: /\.less$/,
        exclude: [/node_modules/],
        use: [
          devMode ? 'style-loader' : MiniCssExtractPlugin.loader,
          {
            loader: 'css-loader',
            options: {
              modules: true,
              sourceMap: true,
              importLoaders: 1,
              minimize: false, // We use PostcssAssetsPlugin instead to minimize result chunks as a whole
              localIdentName: '[name]_[local]_[sha512:hash:base64:3]',
            },
          },
          {
            loader: 'postcss-loader',
            options: {
              sourceMap: true,
            },
          },
          {
            loader: 'less-loader',
          },
        ],
      }
    ],
  },

  plugins: [
    new MiniCssExtractPlugin({
      filename: devMode ? '[name].css' : '[name].[hash].css',
      chunkFilename: devMode ? '[id].css' : '[id].[hash].css',
    })

    new PostCSSAssetsPlugin({
      test: /\.css$/,
      log: true,
      plugins: [
        // Pack same CSS media query rules into one media query rule
        mqpacker,
        // Minify CSS file with source maps. That’s only
        csswring({preservehacks: true, removeallcomments: true}),
      ],
    }),
  ],
};