原生js提交ajax请求

 1 <script type="text/javascript">
 2         window.onload = function(){
 3             var btn = document.getElementById("btn");
 4             var pcontent = document.getElementById("content");
 5             //获取XMLHttpRequest 兼容各种浏览器 包括IE6,IE5
 6             function getXmlHttp(){
 7                 if(window.XMLHttpRequest){
 8                     return  new XMLHttpRequest();
 9                 }else if( window.ActiveXObject){
10                     var version = [
11                         "MSXML2.XMLHttp.6.0",
12                         "MSXML2.XMLHttp.3.0",
13                         "MSXML2.XMLHttp"
14                     ];
15                     for(var i=0;i<version.length;i++){
16                         try { return  new ActiveXObject(version[i]);}catch (e) {}
17                     }
18                 }else{
19                     alert("您的浏览器不支持XMLHttp");
20                 }
21             }
22             btn.onclick = function(){
23                 var xmlHttp = getXmlHttp();
24                 xmlHttp.onreadystatechange = function(){
25                     if(xmlHttp.readyState == 4  ){
26                         if(xmlHttp.status == 200){
27                             pcontent.innerHTML =  xmlHttp.responseText;
28                         }else{
29                             alert("错误信息:"+ xmlHttp.statusText);
30                         }
31                     }
32                 }
33                 xmlHttp.open("GET","data.txt",true);
34                 xmlHttp.send(null);
35             }
36
37         }