JavaScript 实现简洁高效的拖拽功能示例

<!DOCTYPE HTML>
<html>
<head>
 <meta http-equiv="content-type" charset="utf-8" />
  <meta http-equiv="content-type" content="text/html" />
  <title>demo</title>
</head>
<body>
<p>aaaaaaaaaaa</p>
<div id="one" style="height:100px;width:100px;background:red;position:absolute;"></div>
<script>
var odiv=document.getElementById("one");
dra(odiv);
function dra(obj){
  obj.onmousedown=function(e){
    var oe=e||window.event;
    var $this=this;
    var l=oe.clientX-$this.offsetLeft;
    var t=oe.clientY-$this.offsetTop;
    document.onmousemove=function(e){
      var oe=e||window.event;
      var ol=oe.clientX-l;
      var ot=oe.clientY-t;
      if(ol<0) ol=0;
      if(ot<0) ot=0;
      if(ot>document.documentElement.clientHeight-$this.offsetHeight) ot=document.documentElement.clientHeight-$this.offsetHeight;
      if(ol>document.documentElement.clientWidth-$this.offsetWidth) ol=document.documentElement.clientWidth-$this.offsetWidth;
      $this.style.left=ol+"px";
      $this.style.top=ot+"px";
    }
    document.onmouseup=function(){
      document.onmousemove=null;
      document.onmouseup=null;
      if($this.releaseCapture) $this.releaseCapture();
    }
    if($this.setCapture){
      $this.setCapture();
    }
    if(oe.preventDefault) oe.preventDefault();
    else oe.returnValue=false;
    return false;
  }
}
</script>
</body>
</html>