Ajax动态显示

<SCRIPT type=text/javascript>
var xmlhttp;

function send(){
if(window.XMLHttpRequest){
 xmlhttp=new XMLHttpRequest();
 if(xmlhttp.overrideMimeType){
   xmlhttp.overrideMimeType("text/xml");
 }else if(window.ActiveXObject){
  var activexName = ["MSXML2.XMLHTTP","Microsoft.XMLHTTP"];
        for (var i = 0; i < activexName.length; i++) {
            try{
                //取出一个控件名进行创建，如果创建成功就终止循环
                //如果创建失败，回抛出异常，然后可以继续循环，继续尝试创建
                xmlhttp = new ActiveXObject(activexName[i]);
                break;
            } catch(e){     
        }
}
}
if (!xmlhttp) {
        alert("XMLHttpRequest对象创建失败!!");
        return;
    } else {
       
    }
    xmlhttp.onreadystatechange=callback;
    xmlhttp.open("post","news.do?method=QuerySomeNews",true);
    xmlhttp.setRequestHeader("Content-Type","application/x-www-form-urlencoded"); 
    xmlhttp.send(null);
    }

    
 
   
  function callback(){
   if(xmlhttp.readyState==4){
    if(xmlhttp.status==200){
   
     var responseXML=xmlhttp.responseXML;
     var yan=responseXML.getElementsByTagName("response");
      var ta="<table class=STYLE2 width:100% border:0 id=ta>";
       
       for(var i=0;i<yan.length;i++){
       var y=yan[i];
       var title=y.childNodes[0].firstChild.data;
       var time=y.childNodes[1].firstChild.data;
       var nid=y.childNodes[2].firstChild.data;
       ta+="<tr id='aa'><TD align=middle width:14><IMG height:10 src='images/main_icon01.gif' width:10></TD>";
       ta+="<td width=263 align=left><a href='news.do?method=queryById&nid="+nid+"' cursor=hand>"+title+"</a></td>";
       ta+="<td align=right width=88> <DIV align=right><DIV align=right>"+time+"</DIV></DIV></td></tr>";  
       }
     ta+="</table>";
     document.getElementById("res").innerHTML=ta;
     setTimeout("send()",6000);
    
     if(responseXML==null){
      alert("数据没有传过来");
     }else{
     
     } 
    }
   
   }
  }
  }
</SCRIPT>