js遮罩效果详解
对于新手来说，看起来一头雾水！进入页面弹出一个对话框，只能操作当前区域的内容。
在这里面有几个主要的知识，只要掌握这几个就可以轻松的明白原理，可以做出各种各样的效果了。
首页是DOM 这个对于说javascript来说是必须掌握的知识，也就是说js只能通过DOM对象也可以控制HTML里的内容，主要有添加节点;删除节点，创建节点，改变节点的属性等。
遮罩效果主要用到的还是这几个（添加节点;删除节点，创建节点，改变节点的属性）
下面放出源码来看看
<!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>mask</title>
</head>
<body>
<script type="text/javascript">
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.ceil(document.documentElement.clientWidth);
_scrollHeight =Math.ceil(document.documentElement.clientHeight);
newMask.style.width = _scrollWidth + "px";
newMask.style.height = _scrollHeight + "px";
newMask.style.top = "0px";
newMask.style.left = "0px";
newMask.style.background = "#33393C";
newMask.style.filter = "alpha(opacity=20)";
newMask.style.opacity = "0.20";
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) + "px";
newDiv.style.left = (document.body.scrollLeft + document.body.clientWidth/2 - newDivWidth/2) + "px";
newDiv.style.background = "#EFEFEF";
newDiv.style.border = "1px solid #860001";
newDiv.style.padding = "5px";
newDiv.innerHTML = "<h2>弹出层内容</h2>";
document.body.appendChild(newDiv);
//弹出层滚动居中
function newDivCenter()
{
newDiv.style.top = (document.body.scrollTop + document.body.clientHeight/2 - newDivHeight/2) + "px";
newDiv.style.left = (document.body.scrollLeft + document.body.clientWidth/2 - newDivWidth/2) + "px";
}
if(document.all)
{
window.attachEvent("onscroll",newDivCenter);
}
else
{
window.addEventListener('scroll',newDivCenter,false);
}
//关闭新图层和mask遮罩层
var newA = document.createElement("a");
newA.href = "#";
newA.innerHTML = "关闭";
newA.onclick = function()
{
if(document.all)
{
window.detachEvent("onscroll",newDivCenter);
}
else
{
window.removeEventListener('scroll',newDivCenter,false);
}
document.body.removeChild(docEle(_id));
document.body.removeChild(docEle(m));
return false;
}
newDiv.appendChild(newA);
}
</script>
<body>
<a onclick="openNewDiv('newDiv');return false;" style="cursor:pointer">点击弹出遮罩层</a>
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</body>
</html>上面的源码注释的很清楚，希望学习者可以仔细的去观看每一行代码，都有说明。