实例—完美拖拽

window.onload=function(){
var oDiv1=document.getElementById('div1');
var oDiv2=document.getElementById('div2');

drag(oDiv1);
drag(oDiv2);
function drag(obj)
{
obj.onmousedown=function(ev){
var oEvent=ev||event;
var disX=oEvent.clientX-obj.offsetLeft;
var disY=oEvent.clientY-obj.offsetTop;
obj.onmousemove=function(ev){
var oEvent=ev||event;
var left=oEvent.clientX-disX;
var top=oEvent.clientY-disY;

obj.style.left=left+'px';
obj.style.top=top+'px';
};
obj.onmouseup=function(){
obj.onmousemove=null;
obj.onmouseup=null;
obj.releaseCapture&&obj.releaseCapture();
};
obj.setCapture&&obj.setCapture();
return false;
};
}
};

*{margin:0px;padding:0px;}
#div1{width:200px;height:200px;background:red;position:absolute;left:100px;top:100px;}
#div2{width:200px;height:200px;background:green;position:absolute;left:400px;top:100px;}

<div id="div1"></div>
<div id="div2"></div>