webpack.config.js

const Webpack = require("webpack");
const Glob = require("glob");
const path = require("path");
const CopyWebpackPlugin = require("copy-webpack-plugin");
const MiniCssExtractPlugin = require("mini-css-extract-plugin");
const ManifestPlugin = require("webpack-manifest-plugin");
const CleanObsoleteChunks = require('webpack-clean-obsolete-chunks');
const UglifyJsPlugin = require("uglifyjs-webpack-plugin");
const LiveReloadPlugin = require('webpack-livereload-plugin');

const configurator = {
  entries: function () {
    var entries = {
      application: [
        './node_modules/jquery-ujs/src/rails.js',
        './assets/css/application.scss',
      ],
    }

    Glob.sync("./assets/*/*.*").forEach((entry) => {
      if (entry === './assets/css/application.scss') {
        return
      }

      let key = entry.replace(/(\.\/assets\/(js|css|go)\/)|\.(js|s[ac]ss|go)/g, '')
      if (key.startsWith("_") || (/(js|s[ac]ss|go)$/i).test(entry) == false) {
        return
      }

      if (entries[key] == null) {
        entries[key] = [entry]
        return
      }

      entries[key].push(entry)
    })

    return entries
  },

  plugins() {
    var plugins = [
      new CleanObsoleteChunks(),
      new Webpack.ProvidePlugin({ $: "jquery", jQuery: "jquery" }),
      new MiniCssExtractPlugin({ filename: "[name].[contenthash].css" }),
      new CopyWebpackPlugin([{ from: "./assets", to: "" }], { copyUnmodified: true, ignore: ["css/**", "js/**"] }),
      new Webpack.LoaderOptionsPlugin({ minimize: true, debug: false }),
      new ManifestPlugin({ fileName: "manifest.json" })
    ];

    return plugins
  },

  moduleOptions: function () {
    return {
      rules: [
        {
          test: /\.s[ac]ss$/,
          use: [
            MiniCssExtractPlugin.loader,
            { loader: "css-loader", options: { sourceMap: true } },
            { loader: "sass-loader", options: { sourceMap: true } }
          ]
        },
        { test: /\.jsx?$/, loader: "babel-loader", exclude: /node_modules/ },
        { test: /\.(woff|woff2|ttf|svg)(\?v=\d+\.\d+\.\d+)?$/, use: "url-loader" },
        { test: /\.eot(\?v=\d+\.\d+\.\d+)?$/, use: "file-loader" },
        { test: require.resolve("jquery"), use: "expose-loader?jQuery!expose-loader?$" },
        { test: /\.go$/, use: "gopherjs-loader" }
      ]
    }
  },

  buildConfig: function () {
    const env = process.env.NODE_ENV || "development";

    var config = {
      mode: env,
      entry: configurator.entries(),
      output: { filename: "[name].[hash].js", path: `${__dirname}/public/assets` },
      plugins: configurator.plugins(),
      module: configurator.moduleOptions()
    }

    if (env === "development") {
      config.plugins.push(new LiveReloadPlugin({ appendScriptTag: true }))
      return config
    }

    const uglifier = new UglifyJsPlugin({
      uglifyOptions: {
        beautify: false,
        mangle: { keep_fnames: true },
        output: { comments: false },
        compress: {}
      }
    })

    config.optimization = {
      minimizer: [uglifier]
    }

    return config
  }
}

module.exports = configurator.buildConfig()