AJAX相关问题提问
ajax.js

// JavaScript Document 
function createxmlhttp() 
{ 
xmlhttpobj = false; 
try{ 
xmlhttpobj = new XMLHttpRequest; 
}catch(e){ 
try{ 
xmlhttpobj=new ActiveXObject("MSXML2.XMLHTTP"); 
}catch(e2){ 
try{ 
xmlhttpobj=new ActiveXObject("Microsoft.XMLHTTP"); 
}catch(e3){ 
xmlhttpobj = false; 
} 
} 
} 
return xmlhttpobj; 
} 

function getsubcategory(bigclassid){ 
if(bigclassid==0){ 
document.getElementById("subclass").innerHTML="<select name='smallclassid'><option value='0' selected>选择二级分类</option></select>"; 
return; 
}; 
var xmlhttpobj = createxmlhttp(); 
if(xmlhttpobj){//如果创建对象xmlhttpobj成功 
xmlhttpobj.onreadystatechange=handle; 
xmlhttpobj.open('get',"../getsubcategory.asp?unit="+bigclassid+"&name="+Math.random(),true);//get方法 加个随机数。
xmlhttpobj.send(null); 
} 
} 

function handle(){//客户端监控函数 
//if(xmlhttpobj.readystate==4){//服务器处理请求完成 
if(xmlhttpobj.status==200){ 
//alert('ok'); 
var html = xmlhttpobj.responseText;//获得返回值 
document.getElementById("subclass").innerHTML=html; 
}else{ 
document.getElementById("subclass").innerHTML="对不起，您请求的页面有问题..."; 
} 
//} 
//else{ 
//document.getElementById("subclass").innerHTML=xmlhttpobj.readystate;//服务器处理中 
//} 
//} 

} 

getsubcategory.asp

<%@language="vbscript" codepage="936"%> 
<!--#include file="../conn.asp"--> 
<% 
response.charset="gb2312" 
unit=request.querystring("unit")
name_id=request.QueryString("name")
if unit<>"" then 
set re=new regexp 
re.ignorecase=true 
re.global=false 
re.pattern = "^[0-9]{1,3}$" 
if not re.test(unit) then 
response.write "非法参数" 
response.end 
end if%> 

<%on error resume next
sql="select * from wy_user where unit="&unit
set p = user_conn.execute(sql)
if err then 
err.clear 
response.write "查询出错" 
response.end 
end if 
if not p.eof then 
html = "<select name='select2'>"&vbnewline 
do while not p.eof 
html = html&"<option value="&p("E_N")&">"&p("user_name")&"</option>"&vbnewline 
p.movenext 
loop 
html = html&"</select>" 
else 
html = "<option value='0' selected>暂无小类</option>" 
end if 
p.close 
set p = nothing 
conn.close 
set conn = nothing 
response.write html 
end if 
%> 

用户访问的页面（段）

<script language="javascript" type="text/javascript" src="js/ajax.js"></script>
<table>
  <tr>
  <td height="30" align="right" class="left_txt2">单&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;位：</td>
  <td>&nbsp;</td>
  <td height="30">