关于光标在哪里，面板就移动到哪里这样写有问题吗？

function fndown(){

var oDrag = document.getElementById('loginPanel');

var bclientX = oDrag.offsetLeft;

var bclientY = oDrag.offsetTop; 

var aclientX = event.clientX;

var aclientY = event.clientY;

document.onmousemove = function(event){

event = event || window.event;

oDrag.style.left =  (event.clientX - aclientX + bclientX + 'px');

oDrag.style.top =  (event.clientY - aclientY + bclientY + 'px');

}

}