隱藏select，顯示層

<script language="javascript">

// 隱藏被ID爲objID的對象（層）遮擋的所有select
function HideOverSels(objID)
{
    var sels = document.getElementsByTagName('select');
    for (var i = 0; i < sels.length; i++)
      if (Obj1OverObj2(document.all[objID], sels[i]))
        sels[i].style.visibility = 'hidden';         
}

//判斷obj1是否遮擋了obj2
function Obj1OverObj2(obj1, obj2)
{
  var pos1 = getPosition(obj1)
  var pos2 = getPosition(obj2)
  var result = true;
  var obj1Left = pos1.left - window.document.body.scrollLeft;
  var obj1Top = pos1.top - window.document.body.scrollTop;
  var obj1Right = obj1Left + obj1.offsetWidth;
  var obj1Bottom = obj1Top + obj1.offsetHeight;
  var obj2Left = pos2.left - window.document.body.scrollLeft;
  var obj2Top = pos2.top - window.document.body.scrollTop;
  var obj2Right = obj2Left + obj2.offsetWidth;
  var obj2Bottom = obj2Top + obj2.offsetHeight;
 
  if (obj1Right <= obj2Left || obj1Bottom <= obj2Top ||
      obj1Left >= obj2Right || obj1Top >= obj2Bottom)
    result = false;
  return result;
}

// 獲取對象的座標
function getPosition(Obj)
{
 for (var sumTop=0,sumLeft=0;Obj!=window.document.body;sumTop+=Obj.offsetTop,sumLeft+=Obj.offsetLeft, Obj=Obj.offsetParent);
 return {left:sumLeft,top:sumTop}
}
</script>

<script>
    window.onload = function(){HideOverSels("div1")}
</script>

<div style="position: absolute;left:10px;top:20px;width:200px;height:200px;border:1px solid red;" id="div1">
看看這個層下面的select是不是都隱藏了：）
</div>
<select name="">
 <option>test1</option>
 <option>test2</option>
 <option>test3</option>
</select>
<P />

<select name="">
 <option>test1</option>
 <option>test2</option>
 <option>test3</option>
</select>
<P />

<select name="">
 <option>test1</option>
 <option>test2</option>
 <option>test3</option>
</select>
<P />

<select name="">
 <option>test1</option>
 <option>test2</option>
 <option>test3</option>
</select>
<P />

<select name="">
 <option>test1</option>
 <option>test2</option>
 <option>test3</option>
</select>
<P />

<select name="">
 <option>test1</option>
 <option>test2</option>
 <option>test3</option>
</select>
<P />

<select name="">
 <option>test1</option>
 <option>test2</option>
 <option>test3</option>
</select>
<P />

<select name="">
 <option>test1</option>
 <option>test2</option>
 <option>test3</option>
</select>
<P />

<select name="">
 <option>test1</option>
 <option>test2</option>
 <option>test3</option>
</select>
<P />