webpack.config.js

const webpack = require("webpack");
const path = require("path");
const ExtractTextPlugin = require("extract-text-webpack-plugin");
const UglifyJsPlugin = require("uglifyjs-webpack-plugin");
const autoprefixer = require("autoprefixer");

const extractSass = new ExtractTextPlugin({
  filename: "css/[name].css",
});

module.exports = {
  entry: {
    application: "./assets/js/index.js",
    styles: "./assets/sass/application.sass"
  },
  resolve: {
    modules: [path.join(__dirname, "assets/js"), "node_modules"],
    extensions: [".js", ".jsx"],
    alias: {
      modernizr$: path.resolve(__dirname, ".modernizrrc.js")
    }
  },
  output: {
    path: path.resolve(
      __dirname,
      process.env.NODE_ENV === "development"
        ? "./src/assets"
        : "./build/assets"
    ),
    filename: "js/[name].js",
    publicPath: "/assets/"
  },
  optimization: {
    minimizer: [
      new UglifyJsPlugin({
        uglifyOptions: {
          warnings: false,
          compress: true,
          comments: false
        }
      })
    ],
  },
  module: {
    rules: [
      {
        loader: "webpack-modernizr-loader",
        test: /\.modernizrrc\.js$/
      },
      {
        test: /\.js$/,
        exclude: /(node_modules|bower_components)/,
        use: {
          loader: "babel-loader",
          options: {
            presets: ["@babel/preset-env"]
          }
        }
      },
      {
        enforce: "pre",
        test: /\.s?css/,
        use: "import-glob-loader"
      },
      {
        test: /\.s?[ac]ss$/,
        use: extractSass.extract({
          use: [
            { loader: "css-loader" },
            {
              loader: "postcss-loader",
              options: {
                plugins: () => [autoprefixer()]
              }
            },
            { loader: "sass-loader" }
          ],
          fallback: "style-loader"
        })
      },
      {
        test: /\.(png|jpg|gif)$/,
        use: ["file-loader"]
      },
      {
        test: /\.(woff|woff2|eot|ttf|otf|svg)$/,
        use: ["file-loader"]
      }
    ]
  },
  plugins: [
    extractSass,
    new webpack.DefinePlugin({
      "process.env": {
        NODE_ENV: JSON.stringify(process.env.NODE_ENV)
      }
    }),
    new webpack.ProvidePlugin({
      $: "jquery", // Used for Bootstrap JavaScript components
      jQuery: "jquery", // Used for Bootstrap JavaScript components
      Popper: ["popper.js", "default"] // Used for Bootstrap dropdown, popup and tooltip JavaScript components
    })
  ]
};