200KB exploration

src-slash-index.js

import ReactDOM from 'react-dom';

webpack.config.js

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

module.exports = {
  entry: path.resolve('src/index.js'),
  output: {
    filename: 'index.js',
    path: path.resolve('dist'),
  },
  plugins: [
    new webpack.optimize.UglifyJsPlugin({}),
    new webpack.DefinePlugin({
      'process.env.NODE_ENV': JSON.stringify('production'),
    })
  ]
}

1. DefinePlugin should be before the Uglify plugin.
2. The production literal should be in quotes. Otherwise you’re replacing it with an undefined variable called production. This code will just crash at runtime.

The correct way to do it is in the docs

https://reactjs.org/docs/optimizing-performance.html#webpack

I wouldn't expect DefinePlugin order to matter, I imagine they operate on different hooks. Tested order locally and it didn't affect size.

Updating w/ JSON.stringify got us down to ~100KB