javascript 实现简单的div拖动

<script>
var   ms;
function   did(obj){
ms=obj;
event.srcElement.setCapture();
x=document.all(ms).style.pixelLeft-event.x;
y=document.all(ms).style.pixelTop-event.y;
}

function   document.onmousemove(){
if(ms){
document.all(ms).style.pixelLeft=x+event.x;
document.all(ms).style.pixelTop=y+event.y;
}
}

function   document.onmouseup(){
if(ms){
event.srcElement.releaseCapture();
ms=0;
}
}
</script>
<div   id=a1   style=position:absolute>
<div   id=a2   onmousedown=did('a1')>aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa</div>
<div   id=a3>bbbbbbbbbbbbbbbbbbbbbbb</div>
</div>