Ajax按需读取数据生成下级菜单

<script language="javascript"> 
var http_request=false; 
function send_request(url){//初始化,指定处理函数，发送请求的函数 
http_request=false; 
//开始初始化XMLHttpRequest对象 
if(window.XMLHttpRequest){//Mozilla浏览器 
http_request=new XMLHttpRequest(); 
if(http_request.overrideMimeType){//设置MIME类型 
http_request.overrideMimeType("text/html"); 
} 
} 
else if(window.ActiveXObject){//IE浏览器 
try{ 
http_request=new ActiveXObject("Xsxml2.XMLHTTP"); 
http_request.setRequestHeader("Content-Type","text/xml"); 
http_request.setRequestHeader("Content-Type","gb2312"); 
} 
catch(e){ 
try{ 
http_request=new ActiveXObject("Microsoft.XMLHTTP"); 
http_request.setRequestHeader("Content-Type","text/xml"); 
http_request.setRequestHeader("Content-Type","gb2312"); 
} 
catch(e){ 
} 
} 
} 
if(!http_request){//异常，创建对象实例失败 
window.alert("不能创建XMLHttpRequest对象实例"); 
return false; 
} 
http_request.onreadystatechange=processRequest; 
//确定发送请求的方式和URL以及是否同步执行下段代码 
http_request.open("GET",url,true); 
http_request.send(null); 
} 
//处理返回信息的函数 
function processRequest(){ 
if(http_request.readyState==4){//判断对象状态 
if(http_request.status==200){//信息已经成功返回，开始处理信息 
document.getElementById(currentPos).innerHTML=http_request.responseText; 
} 
else{//页面不正常 
alert("您所请求的页面有异常"); 
} 
} 
} 
function showRoles(obj){ 
document.getElementById(obj).parentNode.style.display=""; 
document.getElementById(obj).innerHTML="正在读取数据..." 
currentPos=obj; 
send_request("jilian_data.asp?playPos="+obj); 
} 
</script> 

<table width="200" border="0" cellspacing="0" cellpadding="0"> 
<tr> 
<td height="20"> 
<a href="javascript:void(0)" onclick="showRoles('pos_1')">经理室 
</a> 
</td> 
</tr> 
<tr style="display:none"> 
<td height="20" id="pos_1"> </td> 
</tr> 
<tr> 
<td height="20"> 
<a href="javascript:void(0)" onclick="showRoles('pos_2')">开发部</a> 
</td> 
</tr> 
<tr style="display:none"> 
<td id="pos_2" height="20"> </td> 
</tr> 
</td> 
</table>

<%@LANGUAGE="VBSCRIPT" CODEPAGE="936"%> 
<% 
playPos=request("playPos") 
if playPos="pos_1" then 
Response.Write("  jingli<br>  副总经理") 
end if 
if playPos="pos_2" then 
Response.Write("  总工程师<br>  软件工程师") 
end if 
%>