webpack.config.js

const path = require("path");
const MiniCssExtractPlugin = require("mini-css-extract-plugin");
const webpack = require('webpack');

process.env.NODE_ENV = process.env.NODE_ENV || 'development';
if(process.env.NODE_ENV === 'test'){
  require('dotenv').config({path : '.env.test'});
}else if(process.env.NODE_ENV === 'development'){
  require('dotenv').config({path : '.env.development'});
}

module.exports = (env) => {
  const isProduction = env === "production";

  return {
    entry: ['babel-polyfill',"./src/app.js"],
    output: {
      path: path.join(__dirname, "public", "/dist"),
      filename: "bundle.js",
    },
    module: {
      rules: [
        {
          loader: "babel-loader",
          test: /\.js$/,
          exclude: /node_modules/,
        },
        {
          test: /\.s?css$/,
          use: [
            MiniCssExtractPlugin.loader,
            {
              loader: "css-loader",
              options: {
                sourceMap: true,
                url : false
              },
            },
            {
              loader: "sass-loader",
              options: {
                sourceMap: true,
              },
            },
          ],
        },
      ],
    },
    plugins: [
      new MiniCssExtractPlugin({
        filename: "styles.css",
      }),
      new webpack.DefinePlugin({
        'process.env.FIREBASE_API_KEY' : JSON.stringify(process.env.FIREBASE_API_KEY),
        'process.env.FIREBASE_DATABASE_URL' : JSON.stringify(process.env.FIREBASE_DATABASE_URL),
        'process.env.FIREBASE_AUTH_DOMAIN' : JSON.stringify(process.env.FIREBASE_AUTH_DOMAIN),
        'process.env.FIREBASE_PROJECT_ID' : JSON.stringify(process.env.FIREBASE_PROJECT_ID ),
        'process.env.FIREBASE_STORAGE_BUCKET' : JSON.stringify(process.env.FIREBASE_STORAGE_BUCKET),
        'process.env.FIREBASE_MESSAGING_SENDER_ID' : JSON.stringify(process.env.FIREBASE_MESSAGING_SENDER_ID),
        'process.env.FIREBASE_APP_ID' : JSON.stringify(process.env.FIREBASE_APP_ID),
        'process.env.FIREBASE_MEASUREMENT_ID' : JSON.stringify(process.env.FIREBASE_MEASUREMENT_ID),
      })
    ],
    devtool: isProduction ? "source-map" : "inline-source-map",
    devServer: {
      contentBase: path.join(__dirname, "public"),
      historyApiFallback: true,
      publicPath: "/dist/",
    },
  };
};