JS彈出一個相對位置的浮動層

需求：點擊一個按鈕之後在按鈕下方顯示一個浮出層。

<style type="text/css">
#thelayer{
 width:300px;height:98px;border:#E4F5FD 1px solid;z-index:2;position:absolute;background:#FFFFFF;display:none;
}
</style>

<script>
function CPos(x, y)
{
    this.x = x;
    this.y = y;
}

function GetObjPos(ATarget)
{
    var target = ATarget;
    var pos = new CPos(target.offsetLeft, target.offsetTop);
   
    var target = target.offsetParent;
    while (target)
    {
        pos.x += target.offsetLeft;
        pos.y += target.offsetTop;
       
        target = target.offsetParent
    }
   
    return pos;
}
function showlayer(obj) {
 pos = GetObjPos(obj);
 l = document.getElementById("thelayer");
 l.style.left = pos.x + 40;
 l.style.top = pos.y + 40;
 l.style.display="block";
}
</script>

<div onclick="showlayer(this)">點我</div>

<div id="thelayer">浮我</div>