React production build with webpack

webpack.config.babel.js

import webpack from 'webpack';

export default {
  context: __dirname,
  entry: './index.js',
  output: {
    path: `${__dirname}/__build__`,
    filename: 'bundle.js',
  },
  module: {
    loaders: [
      { test: /\.jsx?$/, exclude: /node_modules/, loader: 'babel' },
    ],
  },
  resolve: {
    extensions: ['', '.js', '.jsx'],
  },
  plugins: (() => {
    // overload -p flag in $ webpack -p
    // for more info on $ webpack -p see: https://webpack.github.io/docs/cli.html#production-shortcut-p
    if (process.argv.indexOf('-p') !== -1) {
      return [
        new webpack.DefinePlugin({
          'process.env': {
            NODE_ENV: JSON.stringify('production'),
          },
        }),
        
        // note that webpack's -p shortcut runs the UglifyJsPlugin (https://github.com/webpack/docs/wiki/optimization)
        // but for some reason leaves in one multiline comment while removing the rest,
        // so have to set comments: false here to remove all the comments
        new webpack.optimize.UglifyJsPlugin({
          output: {
            comments: false,
          },
        }),
      ];
    }
    return [];
  })(),
};

For a basic react and react-router app this creates about a 200kB bundle.js file.