webpack.config.demo.js

const HtmlWebpackPlugin = require('html-webpack-plugin');
const path = require('path');
const webpack = require('webpack');

module.exports = {
    devtool: 'source-map',
    entry: {
        demo: ['@babel/polyfill', './src/index']
    },
    output: {
        path: path.join(__dirname, 'build'),
        filename: 'static/[name].js'
    },
    plugins: [
        new HtmlWebpackPlugin({
            filename: 'index.html',
            inject: true,
            template: './public/index.html'
        }),
        new webpack.DefinePlugin({
            'process.env': {
                'NODE_ENV': JSON.stringify('production')
            }
        })
    ],
    module: {
        rules: [
            {
                test: /\.(js|jsx)$/,
                resolve: {extensions: [".js", ".jsx"]},
                use: ['babel-loader'],
                include: path.join(__dirname, 'src')
            },
            {
                test: /\.css$/,
                use: ['style-loader', 'css-loader']
            }
        ]
    }
}