webpack.config.js

const path = require('path')
const CopyWebpackPlugin = require('copy-webpack-plugin')

module.exports = {
    entry: './app/scripts/index.js',
    mode: 'production',
    output: {
        path: path.resolve(__dirname, 'build'),
        filename: 'app.js'
    },
    plugins: [
        // Copy our app's index.html to the build folder.
        new CopyWebpackPlugin([
            {from: './app/index.html', to: 'index.html'}
        ])
    ],
    devtool: 'source-map',
    module: {
        rules: [
            {
                test: /\.(scss)$/,
                use: [{
                        loader: 'style-loader', // inject CSS to page
                    }, {
                        loader: 'css-loader', // translates CSS into CommonJS modules
                    }, {
                        loader: 'postcss-loader', // Run post css actions
                        options: {
                            plugins: function () { // post css plugins, can be exported to postcss.config.js
                                return [
                                    require('precss'),
                                    require('autoprefixer')
                                ];
                            }
                        }
                    }, {
                        loader: 'sass-loader' // compiles Sass to CSS
                    }]
            },
            {
                test: /\.js$/,
                exclude: /(node_modules|bower_components)/,
                loader: 'babel-loader',
                query: {
                    presets: ['env'],
                    plugins: ['transform-react-jsx', 'transform-object-rest-spread', 'transform-runtime']
                }
            }
        ]
    }
}