webpack.config.js

const HtmlWebpackPlugin = require("html-webpack-plugin");
const MiniCssExtractPlugin = require("mini-css-extract-plugin");

const devMode = process.env.NODE_ENV !== "production";

module.exports = {
    entry: [
        "@babel/polyfill",
        "./src/app/index.js"
    ],
    output: {
        path: __dirname + "/build",
        filename: "bundle.js"
    },
    mode: "development",
    module: {
        rules: [
            {
                test: /\.js$/,
                loader: "babel-loader"
            },
            {
                test: /\.css$/,
                use: [
                    devMode ? "style-loader": MiniCssExtractPlugin.loader,
                    "css-loader"
                ]
            }
        ]
    },
    plugins: [
        new HtmlWebpackPlugin({
            template: "./src/index.html"
        }),
        new MiniCssExtractPlugin({
            filename: "bundle.css"
        })
    ]
}