webpack.config.js

const path = require('path');
const webpack = require('webpack');

module.exports = {
    entry:"./src/app.js",
    output: {
        path: path.join(__dirname,'public'),
        filename: 'bundle.js'
    },
    plugins:[
        new webpack.DefinePlugin({
            'process.env': {
                'NODE_ENV': JSON.stringify('production')
            }
        }),
        new webpack.optimize.UglifyJsPlugin({
            compress: {
                warnings: true
            }
        })
    ],
    module: {
        rules: [
            {
                loader: 'babel-loader',
                test: /\.js$/,
                exclude: /node_modules/
            },
            {
                test: /\.s?css$/,
                use: [
                    "style-loader",
                    "css-loader",
                    "sass-loader"
                ]
            }
        ]
    },
    devtool: 'cheap-module-eval-source-map',
    devServer: {
        contentBase: path.join(__dirname, 'public')
    }
};