超简单js可拖动层代码

超简单js可拖动层代码
<div onmousedown="Drag(this, event)" style="position:absolute;border:1px solid red;background:pink;width:400px;height:300px;"></div>
<script>
function Drag(o, e){
 var e = window.event || e;
 var _x = e.offsetX || e.layerX;
 var _y = e.offsetY || e.layerY;
 document.onmousemove = function(e){
  o.style.filter = 'Alpha(opacity=70)';
  o.style.opacity = '0.7';
  var e = window.event || e;
  o.style.left = e.clientX - _x + 'px';
  o.style.top = e.clientY - _y + 'px';
 }
 document.onmouseup = function(e){
  document.onmousemove = null;
  o.style.filter = o.style.opacity = '';
 }
}
</script>