js实现拖动层效果(亮点:面向对象的js)

<script language="javascript">
  function $(_sId){return document.getElementById(_sId);}
   function moveStart (event, _sId){
debugger;
  var oObj = $(_sId);
  oObj.onmousemove = mousemove;
  oObj.onmouseup = mouseup;
  oObj.setCapture ? oObj.setCapture() : function(){};
  oEvent = window.event ? window.event : event;
  var dragData = {x : oEvent.clientX, y : oEvent.clientY};
  var backData = {x : parseInt(oObj.style.top), y : parseInt(oObj.style.left)};
  function mousemove(){
   var oEvent = window.event ? window.event : event;
   var iLeft = oEvent.clientX - dragData["x"] + parseInt(oObj.style.left);
   var iTop = oEvent.clientY - dragData["y"] + parseInt(oObj.style.top);
   oObj.style.left = iLeft;
   oObj.style.top = iTop;
   dragData = {x: oEvent.clientX, y: oEvent.clientY};  
  }
  function mouseup(){
   var oEvent = window.event ? window.event : event;
   oObj.onmousemove = null;
   oObj.onmouseup = null;
   if(oEvent.clientX < 1 || oEvent.clientY < 1 || oEvent.clientX > document.body.clientWidth || oEvent.clientY > document.body.clientHeight){
    oObj.style.left = backData.y;
    oObj.style.top = backData.x;
   }
   oObj.releaseCapture ? oObj.releaseCapture() : function(){};
  }
 }
</script>
<div id="mov" style="position:absolute;height:50px;width:300px;background-color:#FF33ff;top:20px;left:100px;" onMouseDown="javascript:moveStart(event,'mov');"></div>