原生ajax异步请求问题--3次握手

来源：互联网发布：时间都去哪儿了知乎编辑：程序博客网时间：2024/06/16 00:28

1 前端代码

<script> var xmlHttpReq = null;  //IE浏览器使用ActiveX  if (window.ActiveXObject) {  xmlHttpReq = new ActiveXObject("Microsoft.XMLHTTP");  }  //其它浏览器使用window的子对象XMLHttpRequest  else if (window.XMLHttpRequest) {  xmlHttpReq = new XMLHttpRequest();  }var xmlHttpReq = new XMLHttpRequest();  xmlHttpReq.onreadystatechange = function () {if (xmlHttpReq.readyState == 4 && xmlHttpReq.status == 200) { console.log(xmlHttpReq.responseText)   //console出"ccccc"}else {console.log("fail")            ////console出fail  3次    }  } xmlHttpReq.open("get", "http://127.0.0.1:8888?cod=aa"); xmlHttpReq.send();   </script> </body>

2 后端代码

var http=require('http');var app=http.createServer(function(req,res){res.writeHead(200,{"content-type":"text/plain","Access-Control-Allow-Origin":"*"});res.end("ccccc")})app.listen(8888,function(){console.log("server is running")})

结果是：前端先console出3个fail在console出"ccccc"
应为前端要3次握手之后才有数据返回

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