JS拖动技术 关于setCapture使用

JS拖动技术--- 关于setCapture (转自 剑胆琴心-.Net学习笔记)

<script type="text/javascript"> 
<!-- 
window.onload=function(){ 
objDiv = document.getElementById('drag'); 
drag(objDiv); 
}; 
function drag(dv){ 
dv.onmousedown=function(e){ 
var d=document; 
e = e || window.event; 
var x= e.layerX || e.offsetX; 
var y= e.layerY || e.offsetY; 
//设置捕获范围 
if(dv.setCapture){ 
dv.setCapture(); 
}else if(window.captureEvents){ 
window.captureEvents(Event.MOUSEMOVE | Event.MOUSEUP); 
} d.onmousemove=function(e){ 
e= e || window.event; 
if(!e.pageX)e.pageX=e.clientX; 
if(!e.pageY)e.pageY=e.clientY; 
var tx=e.pageX-x; 
var ty=e.pageY-y; 
dv.style.left=tx; 
dv.style.top=ty; 
}; 
d.onmouseup=function(){ 
//取消捕获范围 
if(dv.releaseCapture){ 
dv.releaseCapture(); 
}else if(window.captureEvents){ 
window.captureEvents(Event.MOUSEMOVE|Event.MOUSEUP); 
} 
//清除事件 
d.onmousemove=null; 
d.onmouseup=null; 
}; 
}; 
} 
//--> 
</script> 
<div id="drag" style="position:absolute;left:12px;top:24px;width:100;height:150;border:1px solid #000000;z-index:1;background:#eeeeee">drag me</div>