webpack.server.js

// webpack.server.js
const path = require('path');
const nodeExternals = require('webpack-node-externals');

module.exports = {
  target: 'node',
  mode: 'development',
  externals: [nodeExternals()],
  entry: './server/index.js',
  output: {
    filename: 'server.js',
    path: path.resolve(__dirname, 'prod'),
  },
  module: {
    rules: [
      {
        test: /\.(js|jsx)$/,
        exclude: /node_modules/,
        use: {
          loader: 'babel-loader',
          options: {
            presets: [
              '@babel/preset-env',
              '@babel/preset-react',
            ],
          },
        },
      },
      {
        test: /\.css$/,
        use: [
          'style-loader',
          'css-loader',
        ]
      },
      {
        test: /\.s[ac]ss$/i,
        use: [
          'style-loader',
          'css-loader',
          'sass-loader'
        ]
      }
    ],
  },
  resolve: {
    extensions: ['.js', '.jsx'],
  },
};