兼容地获得XMLHttpRequest对象：

var xhr = null;
if(window.XMLHttpRequest){  //非IE浏览器
      xhr = window.XMLHttpRequest;
}else if(window.ActiveXObject){  //IE浏览器
      try{           //高版本，受msxml3.dll+支持
             xhr = new ActiveXObject("Msxml2.XMLHTTP");
      }catch(e){
             try{       // 低版本，msxml2.6以下版本使用
                    xhr = new ActiveXObject("Microsoft.XMLHTTP");
             }catch(e){ 
                    alert("IE浏览器无法创建ActiveXObject对象！");
             }
      }
}

xhr.open("POST",url,true);
xhr.setRequestHeader("Content-Type","application/x-www-form-urlencoded");
xhr.onreadystatechange=stateChangeHandler;
xhr.send();  //var name="clf";   xhr.send(name);
function stateChangeHandler(){
      if(xhr.readystate==4&&xhr.status==200){
            var obj = document.getElementById("targetDiv");
	    obj.innerHTML = xhr.responseText;
      }
}