nodejs 報錯 res未定義？

運行nodejs時報錯res未定義，幫忙看下為什么？

var http = require('http')
var path = require('path')
var fs = require('fs')
var url = require('url')
var server = http.createServer(function(req, res){
   var pathObj = url.parse(req.url, true)
  console.log(pathObj)
  console.log("我愛你中國~")
  console.log(req)

})
fs.readFile('./hello.html',function(err,fileContent){
    if(err){
        console.log(404)
        res.writeHead(404,'not found')
        res.end()
        }else{
             res.writeHead(200, 'OK')
             console.log('OK')
            res.write(fileContent)
            res.end()

        }

    
})

server.listen(8080)