关闭窗口的操作 xmlhttp 的post取不到值, get取得到值,该如何解决

关闭窗口的操作 xmlhttp 的post取不到值, get取得到值
POST方式：   取不到值

<script   language= "javascript ">
window.onbeforeunload   =   function()
{
    var   n   =   window.event.screenX   -   window.screenLeft;
    var   b   =   n   >   document.documentElement.scrollWidth-20;
    if(b   &&   window.event.clientY   <   0   ||   window.event.altKey)
    {
var   xmlhttp   =   new   ActiveXObject( "Microsoft.XMLHTTP ");
ListString   =   "action=dl&qty=2&dID_1=39&dt_1=2000&dht_1=0&dID_2=44&dt_2=1000&dht_2=0 "
var   Url   =   "tttt.asp "
        xmlhttp.open( "post ",   Url,   false);
xmlhttp.setRequestHeader( "Content-Length ",ListString.length);    
        xmlhttp.setRequestHeader( "Content-Type ", "application/x-www-form-urlencode ")
        xmlhttp.send(ListString);

alert(xmlhttp.responseText);
    }
}
</script>
------------------------

GET方式：   可以取到值

<script   language= "javascript ">
window.onbeforeunload   =   function()
{
    var   n   =   window.event.screenX   -   window.screenLeft;
    var   b   =   n   >   document.documentElement.scrollWidth-20;
    if(b   &&   window.event.clientY   <   0   ||   window.event.altKey)
    {
var   xmlhttp   =   new   ActiveXObject( "Microsoft.XMLHTTP ");
        xmlhttp.open( "get ",   "tttt.asp?action=dl&qty=2&dID_1=39&dt_1=2000&dht_1=0&dID_2=44&dt_2=1000&dht_2=0 ",   false);
        xmlhttp.send();
alert(xmlhttp.responseText);

    }
}
</script>

------------------------

tttt.asp

action=Replace(trim(Request( "action ")), " ' ", " ")
qty=Replace(trim(CLng(Request( "qty "))), " ' ", " ")
dID_1=Replace(trim(CLng(Request( "dID_1 "))), " ' ", " ")
dt_1=Replace(trim(CLng(Request( "dt_1 "))), " ' ", " ")
dht_1=Replace(trim(CLng(Request( "dht_1 "))), " ' ", " ")
dID_2=Replace(trim(CLng(Request( "dID_2 "))), " ' ", " ")
dt_2=Replace(trim(CLng(Request( "dt_2 "))), " ' ", " ")
dht_2=Replace(trim(CLng(Request( "dht_2 "))), " ' ", " ")

Response.Write   action& "　 "&qty& "　 "&dID_1& "　 "&dt_1& "　 "&dht_1& "　 "&dID_2& "　 "&dt_2& "　 "&dht_2
Response.End
------------------------


把     Request改为   Request.Form   ，POST也一样取不到值

请问，是哪里出了问题？谢谢！！


------解决方案--------------------
open后这样吧.
xmlhttp.onreadystatechange=function() {
if (xmlhttp.readyState==4) {
alert(xmlhttp.responseText)
}