增加弹出层的拖拽功能

//背景层加入页面
//以下部分实现弹出层的拖拽效果
var posX;
var posY;
Idiv.onmousedown=function(e)
{
if(!e) e = window.event; //IE
posX = e.clientX - parseInt(Idiv.style.left);
posY = e.clientY - parseInt(Idiv.style.top);
document.onmousemove = mousemove;
}
document.onmouseup = function()
{
document.onmousemove = null;
}
function mousemove(ev)
{
if(ev==null) ev = window.event;//IE
Idiv.style.left = (ev.clientX - posX) + "px";
Idiv.style.top = (ev.clientY - posY) + "px";
}
 
}
function closeDiv() //关闭弹出层
{
var Idiv=document.getElementById("Idiv");
Idiv.style.display="none";
document.body.style.overflow = "auto"; //恢复页面滚动条
var body = document.getElementsByTagName("body");
var mybg = document.getElementById("mybg");
body[0].removeChild(mybg);
}