XMLHttpRequest的使用方法

这里写个使用XMLHttpRequest调用页面，post数据的js。

 1 var xhr=false;
 2  if(window.XMLHttpRequest) {
 3   xhr=new XMLHttpRequest();//IE7+,Firefox,Opera,Chorme,Safari
 4             } else {
 5                 try {
 6                     xhr=new ActiveXObject("MSXML2.XMLHTTP");//IE6+
 7                 }catch(e){
 8                     try {
 9                         xhr=new ActiveXObject("Microsoft.XMLHTTP");//IE6也行
10   }catch(e){return null;}
11  }
12 }
13 
14 str = "Id=" + document.getElementById("Id").value; 
15 xhr.open("POST","http://XXX.XXX.XXX",false);
16 xhr.setRequestHeader("Content-Length",str.length); 
17 xhr.setRequestHeader("CONTENT-TYPE","application/x-www-form-urlencoded");
18 xhr.setRequestHeader("HeaderInfo",document.getElementById("HeaderInfo").value); 
19 xhr.send(str);
20 txt1.document.write(xhr.responseText);
21