webpack.config.js

var path = require('path');
var MiniCssExtractPlugin = require("mini-css-extract-plugin");
var devMode = process.env.NODE_ENV !== 'production';
module.exports = {
    plugins: [
        new MiniCssExtractPlugin({
            filename: devMode ? '[name].css' : '[name].[hash].css',
            chunkFilename: devMode ? '[id].css' : '[id].[hash].css',
        })
    ],
    entry: './src/index.js',
    output: {
        path: path.resolve(__dirname, 'build'),
        filename: 'index.js',
        libraryTarget: 'commonjs2'
    },
    module: {
        rules: [
            {
                test: /\.(js|jsx)$/,
                exclude: /(node_modules|build)/,
                loader: 'babel-loader'
            },
            {
                test: /\.(sa|sc|c)ss$/,
                use: [
                    devMode ? 'style-loader' : MiniCssExtractPlugin.loader,
                    'css-loader'
                ],
            },
        ]
    },
    externals: {
        'react': 'commonjs react'
    }
};