webpack.server.js

const path = require('path');
const nodeExternals = require('webpack-node-externals');
const webpack = require('webpack');

module.exports = {
    entry: './server/index.js',

    target: 'node',

    externals: [nodeExternals()],

    output: {
        path: path.resolve('server-build'),
        filename: 'index.js'
    },

    module: {
        rules: [
            {
                test: /\.js$/,
                exclude: /(node_modules)/,
                use: 'babel-loader'
            },
            {
                test: /\.css$/,
                exclude: /(node_modules)/,
                use: 'css-loader'
            }
        ]
    }, 
    plugins: [
        new webpack.HotModuleReplacementPlugin()
    ],
    devServer: {
        hot: true,
        historyApiFallback: true
    }
};