怎么判断鼠标是否在div的滚动条上？（现在没分，但我一定会追加）帮忙

<html>
<head>
<style type="text/css">
#divTest{ width:120px; height:250px;border:1px solid #CC6600; background-color:#FFFFCC; overflow:auto;}
body{margin:0px;padding:0px}
</style>
<script language="JavaScript">
<!--
var $ = document.getElementById;
function addContent(){
    $("divTest").innerHTML += "asdfasdfasdfasdfasdfasdf<BR>";
}
function isOnScrollBar(){
    
}
 function getPosition(obj) {
    var top=0;
    var left=0;
    var width=obj.clientWidth;
    var height=obj.clientHeight;
while (obj.offsetParent) {
    top += obj.offsetTop;
    left += obj.offsetLeft;
    obj = obj.offsetParent;
    }
    return {"top":top,"left":left,"width":width,"height":height};
 }window.onload = function(){  
    var d = $("divTest");
    var o = getPosition(d);
    var left= o.left+parseInt(d.currentStyle.borderLeftWidth)+parseInt(d.currentStyle.paddingLeft);
    var top =o.top+parseInt(d.currentStyle.borderTopWidth)+ parseInt(d.currentStyle.paddingTop );
    $("divTest").onmousemove = function(){
            var cw = this.clientWidth;
            var ch = this.clientHeight;
            var e = window.event;
            var x = e.x;
            var y = e.y;            if(left+cw < x){ 
                out("x=",x," y=",y," clientWidth:",cw," clientHeight:",ch,"在竖滚动条上");
                return;}
            if(top+ch<y){
                out("x=",x," y=",y," clientWidth:",cw," clientHeight:",ch,"在横滚动条上");
                return;}
            out("x=",x," y=",y," clientWidth:",cw," clientHeight:",ch,"不在滚动条上");
        };
    $("divSt").innerHTML = "left:" + left + " top:" + top + " width:"+o.width+" height:"+o.height;
    $("divSt").innerHTML += " scrollWidth:"+d.scrollWidth+ " scrollHeight:" + d.scrollHeight;
    $("btnAdd").onclick = addContent;
};
function out(){
var ar = [];
    for(var i=0;i<arguments.length;i++)
        ar.push(arguments[i]);
    ar.push("<BR>");
    var div = $("divOut");
    div.innerHTML =  ar.join("") + div.innerHTML;
    //$("divOut").scrollTop=888888;
}
//-->
</script></head>
<body>
<div id="divTest"></div>
<input type="button" value="Add" id="btnAdd">
<div id="divSt" style="width:100%;"></div>
<div id="divOut" style="width:100%;"></div>
</body>
</html>目前的结果有一个像素的偏差,但我不知道在哪里.在IE下基本可以找到位置了