example

// start.js
import React from 'react'
import ReactDOM from 'react-dom'

import { hot } from 'react-hot-loader'

export default function start() {

  const App = () => <div>Hello World!! 4</div>
  const HotApp = hot(module)(App)

  ReactDOM.render(<HotApp />, document.getElementById('root'))

}

// main.js
import start from './start'

start()