Webpack 4 compression optimizations

Common.webpack.jk

const devMode = process.env.NODE_ENV !== "production" || process.env.NODE_ENV !== "development_prod";
const path = require("path");
const glob = require("glob-all");
const MiniCssExtractPlugin = require("mini-css-extract-plugin");
const HtmlWebpackPlugin = require("html-webpack-plugin");
const UglifyJsPlugin = require("uglifyjs-webpack-plugin");
const CompressionPlugin = require("compression-webpack-plugin");
const PurgecssPlugin = require("purgecss-webpack-plugin");
const OptimizeCssAssetsPlugin = require("optimize-css-assets-webpack-plugin");
// const OfflinePlugin = require('offline-plugin');

const PATHS = {
  src: path.join(__dirname, "client")
};

module.exports = {
  entry: "./client/index.js",
  module: {
    rules: [
      {
        test: /\.js$/,
        exclude: /node_modules/,
        use: {
          loader: "babel-loader"
        }
      },
      {
        test: /\.scss$/,
        exclude: /node_modules/,
        use: [devMode ? "style-loader" : MiniCssExtractPlugin.loader, "css-loader", "sass-loader"]
      },
      {
        test: /\.css$/,
        use: [
          {
            loader: MiniCssExtractPlugin.loader
          },
          "css-loader"
        ]
      },
      {
        test: /\.(graphql|gql)$/,
        exclude: /node_modules/,
        use: {
          loader: "graphql-tag/loader"
        }
      }
    ]
  },
  plugins: [
    new HtmlWebpackPlugin({
      template: "client/index.html"
    }),
    new MiniCssExtractPlugin({
      filename: devMode ? "[name].css" : "[name].[hash].css",
      chunkFilename: devMode ? "[id].css" : "[id].[hash].css"
    }),
    new OptimizeCssAssetsPlugin({
      // assetNameRegExp: /\.optimize\.css$/g,
      assetNameRegExp: /\.css$/,
      cssProcessor: require("cssnano"),
      cssProcessorOptions: { safe: true, discardComments: { removeAll: true } },
      canPrint: true
    }),
    // new PurgecssPlugin({
    //   paths: glob.sync(`${PATHS.src}/**/*`,  { nodir: true })
    // }),
    new CompressionPlugin({
      test: /\.js$|\.css$|\.html$/
    })
  ],
  optimization: {
    minimizer: [new UglifyJsPlugin({ sourceMap: true, cache: true })],
    splitChunks: {
      chunks: "all",
      cacheGroups: {
        styles: {
          name: "styles",
          test: /\.css$/,
          chunks: "all",
          enforce: true
        }
      }
    }
  }
};