js拖动层

模仿网易彩票网（http://caipiao.163.com/）的登陆框自己做了一个拖动层，不过有点小问题——在谷歌浏览拖动的时候鼠标状态变成了文字状态（cursor:text;)
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">

<head>

<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />

<title>js拖动层</title>

<style>

body{padding:0; margin:0; width:100%; height:100%;}

* html,* html body{background-image:url(about:blank);background-attachment:fixed}

#dragWp{width:100%; height:100%; position:fixed; left:0; top:0; z-index:99999999; _position:absolute;_left:expression(eval(document.documentElement.scrollLeft));_top:expression(eval(document.documentElement.scrollTop))}

#dragBg{ width:100%; height:100%; background-color:#000; position:absolute; left:0; top:0; opacity:0.4; filter:alpha(opacity=40);}

#dragMain{width:200px;height:100px;position:absolute; border:1px solid #999;line-height:30px;font-size:16px;text-align:center; background-color:#FFF;}

#dragTitle{ width:100%; height:40px; line-height:40px; background-color:#ccc; cursor:move;}

#close{float:right; margin-right:5px; z-index:999; font-size:12px; font-style:normal; cursor:pointer;}

</style>

</head>

<body>

<div style="height:1200px; text-align:center;">

    <h1>hello world</h1>

</div>

<div id="dragWp">

    <div id="dragBg"></div>

    <div id="dragMain">

        <div id="dragTitle">

            <em id="close">关闭</em>拖动层

        </div>

        hello world

    </div>

</div>

<script>

window.onload=function(){

    var dragWp=document.getElementById("dragWp");

    var dragMainId=document.getElementById("dragMain");

    var w=dragWp.offsetWidth;

    var h=dragWp.offsetHeight;

    dragMainId.style.left=(w-dragMainId.offsetWidth)/2+"px";

    dragMainId.style.top=(h-dragMainId.offsetHeight)/2+"px";

}

function dragTemp(dragWp,dragMainId,dragTitleId,closeId,opacity){

    var dragWp=document.getElementById(dragWp);

    var dragMainId=document.getElementById(dragMainId);

    var dragTitleId=document.getElementById(dragTitleId);

    var closeId=document.getElementById(closeId);

    var posX,posY,x,y;

    dragTitleId.onmousedown=function(e){

        var e = e || window.event;

        posX=e.clientX-dragMainId.offsetLeft; //鼠标距离拖动层左侧的距离

        posY=e.clientY-dragMainId.offsetTop;  //鼠标距离拖动层上侧的距离

        dragMainId.style.opacity=opacity;

        dragMainId.style.filter="alpha(opacity="+opacity*100+")";

        document.onmousemove=function(e){

            var e = e || window.event;

            x=e.clientX-posX;

            y=e.clientY-posY;

//            if(x<=0) x=0;    //不允许移出左边

//            else if(x>=document.body.clientWidth-dragMainId.offsetWidth) x=document.body.clientWidth-dragMainId.offsetWidth; //不允许移出右边

            dragMainId.style.left=x+"px";

            dragMainId.style.top=y+"px";

            dragTitleId.style.cursor="move";

            document.onselectstart=function(){ return false } //拖动不选中文字

        }

    };

    document.onmouseup=function(){

        document.onmousemove=null;

        dragMainId.style.opacity=1;

        dragMainId.style.filter="alpha(opacity=100)";

    }

    if(closeId){

        closeId.onclick=function(){

            dragWp.style.display="none";

        }

    }

}

function drag(args){

    dragTemp(args.dragWp,

             args.dragMainId,

             args.dragTitleId,

             args.closeId || null,

             args.opacity || 1)

}

//调用

drag({dragWp:"dragWp",dragMainId:"dragMain",dragTitleId:"dragTitle",closeId:"close",opacity:0.5});

</script>

</body>

</html>
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