HereIsJade/db

## db
100

## index.html
<!DOCTYPE html>
<html>
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width">
  <title>JSONP demo</title>
</head>
<body>
  <p>Your current balance is $<span id="amount">$$$amount$$$</span></p>
  <button id="payBtn">Pay $1</button>
  <script>

    payBtn.addEventListener('click',()=>{
    	let script = document.createElement('script')
      let functionName = `my${parseInt(Math.random()*10000000 ,10)}`
      window[functionName] = (res)=>{
    		console.log(res)
    		if(res.success){
			    amount.innerText = res.amount
        }
      }
      console.log(window[functionName])
      script.src = `http://jack.com:8002/pay?callback=${functionName}`

      document.body.appendChild(script)
      script.onload = (e)=>{
    		e.currentTarget.remove()
	      delete window[functionName]
    	}
      script.onerror = (e)=>{
    		alert('fail')
	      e.currentTarget.remove()
	      delete window[functionName]
    	}

    })
  </script>
</body>
</html>

## server.js
let http = require('http')
let fs = require('fs')
let url = require('url')
let port = process.argv[2]

if(!port){
	console.log('Please specify a port number\nExample: node server.js 8888')
	process.exit(1)
}

let server = http.createServer(function(request, response){
  let parsedUrl = url.parse(request.url, true)
  let pathWithQuery = request.url
  let queryString = ''
  if(pathWithQuery.indexOf('?') >= 0){ queryString = pathWithQuery.substring(pathWithQuery.indexOf('?')) }
  let path = parsedUrl.pathname
  let query = parsedUrl.query
  let method = request.method

  console.log('HTTP path is\n' + pathWithQuery)

  if(path === '/'){
    let HTMLstring = fs.readFileSync('./index.html', 'utf-8')
    let amount = fs.readFileSync('./db', 'utf-8') // read from db

    HTMLstring = HTMLstring.replace('$$$amount$$$', amount)
    response.statusCode = 200
    response.setHeader('Content-Type', 'text/html;charset=utf-8')
    response.write(HTMLstring)
    response.end()
  }
  else if(path === '/pay'){
	  let amount = fs.readFileSync('./db', 'utf-8') // read from db
    let newBalance = amount - 1
    fs.writeFileSync('./db', newBalance)
    response.setHeader('Content-Type', 'application/javascript')
    response.statusCode = 200

    response.write(`
      ${query.callback}({
        'success': true,
        'amount': ${newBalance}
      })
    `)
    response.end()
  }
  else{
    response.statusCode = 404
    response.setHeader('Content-Type', 'text/html;charset=utf-8')
    response.write('404 not found')
    response.end()
  }

})

server.listen(port)
console.log('Listening on ' + port + ' success\nPlease visit http://localhost:' + port)
	<!DOCTYPE html>
	<html>
	<head>
	<meta charset="utf-8">
	<meta name="viewport" content="width=device-width">
	<title>JSONP demo</title>
	</head>
	<body>
	<p>Your current balance is $<span id="amount">$$$amount$$$</span></p>
	<button id="payBtn">Pay $1</button>
	<script>

	payBtn.addEventListener('click',()=>{
	let script = document.createElement('script')
	let functionName = `my${parseInt(Math.random()*10000000 ,10)}`
	window[functionName] = (res)=>{
	console.log(res)
	if(res.success){
	amount.innerText = res.amount
	}
	}
	console.log(window[functionName])
	script.src = `http://jack.com:8002/pay?callback=${functionName}`

	document.body.appendChild(script)
	script.onload = (e)=>{
	e.currentTarget.remove()
	delete window[functionName]
	}
	script.onerror = (e)=>{
	alert('fail')
	e.currentTarget.remove()
	delete window[functionName]
	}

	})
	</script>
	</body>
	</html>
	let http = require('http')
	let fs = require('fs')
	let url = require('url')
	let port = process.argv[2]

	if(!port){
	console.log('Please specify a port number\nExample: node server.js 8888')
	process.exit(1)
	}

	let server = http.createServer(function(request, response){
	let parsedUrl = url.parse(request.url, true)
	let pathWithQuery = request.url
	let queryString = ''
	if(pathWithQuery.indexOf('?') >= 0){ queryString = pathWithQuery.substring(pathWithQuery.indexOf('?')) }
	let path = parsedUrl.pathname
	let query = parsedUrl.query
	let method = request.method

	console.log('HTTP path is\n' + pathWithQuery)

	if(path === '/'){
	let HTMLstring = fs.readFileSync('./index.html', 'utf-8')
	let amount = fs.readFileSync('./db', 'utf-8') // read from db

	HTMLstring = HTMLstring.replace('$$$amount$$$', amount)
	response.statusCode = 200
	response.setHeader('Content-Type', 'text/html;charset=utf-8')
	response.write(HTMLstring)
	response.end()
	}
	else if(path === '/pay'){
	let amount = fs.readFileSync('./db', 'utf-8') // read from db
	let newBalance = amount - 1
	fs.writeFileSync('./db', newBalance)
	response.setHeader('Content-Type', 'application/javascript')
	response.statusCode = 200

	response.write(`
	${query.callback}({
	'success': true,
	'amount': ${newBalance}
	})
	`)
	response.end()
	}
	else{
	response.statusCode = 404
	response.setHeader('Content-Type', 'text/html;charset=utf-8')
	response.write('404 not found')
	response.end()
	}

	})

	server.listen(port)
	console.log('Listening on ' + port + ' success\nPlease visit http://localhost:' + port)