webpack.config.js

const path = require("path")
const webpack = require("webpack")
const NodePolyfillPlugin = require("node-polyfill-webpack-plugin")
const mode = process.env.NODE_ENV === 'development' ? 'development' : 'production';
// Extracts CSS into .css file
const MiniCssExtractPlugin = require('mini-css-extract-plugin');
// Removes exported JavaScript files from CSS-only entries
// in this example, entry.custom will create a corresponding empty custom.js file
const RemoveEmptyScriptsPlugin = require('webpack-remove-empty-scripts');

module.exports = {
  mode,
  entry: {
    bundle: "./app/javascript/bundle.js",
    rails_admin: "./app/javascript/rails_admin.js"
  },
  output: {
    filename: "[name].js",
    sourceMapFilename: "[file].map",
    path: path.resolve(__dirname, "app/assets/builds"),
  },
  module: {
    rules: [
      // Add CSS/SASS/SCSS rule with loaders
      {
        test: /\.(?:sa|sc|c)ss$/i,
        use: [
          MiniCssExtractPlugin.loader,
          'css-loader',
          {
            loader: 'sass-loader',
            options: {
              implementation: require('sass'),
            },
          },
        ],
      },
    ],
  },
  resolve: {
    // Add additional file types
    extensions: ['.js', '.jsx', '.scss', '.css'],
    alias: {
      jquery: "jquery/src/jquery"
    }
  },
  plugins: [
    new webpack.optimize.LimitChunkCountPlugin({
      maxChunks: 1
    }),
    new RemoveEmptyScriptsPlugin(),
    new MiniCssExtractPlugin(),
    new NodePolyfillPlugin()
  ],
  optimization: {
    moduleIds: 'deterministic',
  }
}