content: import express from 'express'
  import React from 'react'
  import ReactDOMServer from 'react-dom/server'
  import Counter from './components/Counter'
  
  // init express
  const app = express()
  
  // add static path
  app.use(express.static('public'))
  
  // add top page routing
  app.get('/', (req, res) => {
    res.send(
      ReactDOMServer.renderToString(
        <div>
          <div id="app">
            <Counter />
          </div>
          <script src="client.js" />
        </div>
      )
    )
  })
  
  // start listen
  app.listen(3000, () => {
    console.log('Example app listening on port 3000!');
  })
  