webpack.prod.js

const { merge } = require('webpack-merge');
const TerserPlugin = require('terser-webpack-plugin');
const MiniCssExtractPlugin = require('mini-css-extract-plugin');
const CssMinimizerPlugin = require('css-minimizer-webpack-plugin');
const common = require('./webpack.common.js');

module.exports = merge(common, {
  mode: 'production',
  devtool: 'source-map',
  optimization: {
    minimizer: [
      new TerserPlugin({
        parallel: true
      }),
      new CssMinimizerPlugin()
    ]
  },
  plugins: [
    new MiniCssExtractPlugin({
      filename: '[name].[hash].css',
      chunkFilename: '[id].[hash].css'
    })
  ],
  module: {
    rules: [{
      test: /\.scss$/i,
      use: [{
        loader: MiniCssExtractPlugin.loader // extract css to separate file
      }, {
        loader: 'css-loader',
        options: {
          url: false
        }
      }, {
        loader: 'sass-loader'
      }]
    }]
  }  
});