Ajax

var xhr = new XMLHttpRequest();//创建Ajax// readyState获取状态的值console.log(xhr.readyState);//=>0 初始化请求代理对象xhr.open("GET","test.php");//请求地址console.log(xhr.readyState);//=>1 open()被调用后,建立一个与服务端的连接xhr.send();//发送请求// onreadystatechange状态发生改变就执行该事件xhr.addEventListener("readystatechange",function(){ ???if(this.readyState == 2){ ???????// =>2 可以获取响应报文的响应头 ???????// getAllResponseHeaders()响应头 ???????console.log(this.getAllResponseHeaders()); ???????// date: Thu, 13 Sep 2018 01:04:51 GMT ???????// server: Apache/2.4.34 (Win64) OpenSSL/1.0.2o PHP/7.2.9 ???????// connection: Keep-Alive ???????// x-powered-by: PHP/7.2.9 ???????// content-length: 9 ???????// keep-alive: timeout=5, max=45 ???????// content-type: text/html; charset=UTF-8 ???????console.log(this.getResponseHeader("date"));//获取单个响应头 ???}else if(this.readyState == 3){ ???????// =>3 正在下载响应报文的响应体 ???}else if(this.readyState == 4){ ???????// =>4 已经接收到了响应报文的响应体 ???????// responseText 响应体 ???????console.log(this.responseText); ???}});

var xhr = new XMLHttpRequest();xhr.open("GET","test.php");xhr.send();xhr.onload = function(){//HTML5的事件.低版本不支持 ???console.log(this.readyState); ???console.log(this.responseText);}