JavaScript 遮罩层 弹出框

<script type="text/javas
cript">
var docEle = function() {
    return document.getElementById(arguments[0]) || false;
}
function openNewDiv(_id){
    var m = "mask";
    if (docEle(_id)) document.body.removeChild(docEle(_id));
    if (docEle(m)) document.body.removeChild(docEle(m));
    //mask遮罩层
    var newMask = document.createElement("div");
    newMask.id = m;
    newMask.style.position = "absolute";
    newMask.style.zIndex = "1";
    _scrollWidth = Math.max(document.body.scrollWidth,document.documentElement.scrollWidth);
    _scrollHeight = Math.max(document.body.scrollHeight,document.documentElement.scrollHeight);
    newMask.style.width = _scrollWidth + "px";
    newMask.style.height = _scrollHeight + "px";
    newMask.style.top = "0px";
    newMask.style.left = "0px";
    newMask.style.background = "yellow";
    newMask.style.filter = "alpha(opacity=40)";
    newMask.style.opacity = "0.40";
    document.body.appendChild(newMask);
    //新弹出层
    var newDiv = document.createElement("div");
    newDiv.id = _id;
    newDiv.style.position = "absolute";
    newDiv.style.zIndex = "9999";
    newDivWidth = 400;
    newDivHeight = 200;
    newDiv.style.width = newDivWidth + "px";
    newDiv.style.height = newDivHeight + "px";
    newDiv.style.top = (document.body.scrollTop + document.body.clientHeight/2 - newDivHeight/2) + &quo