js弹出层，并且遮罩下面内容， [ 注意，这里button为input其中的一种类型，不要换]
<!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>
<title>点击弹出居中的遮罩层代码</title>
<meta http-equiv="content-type" content="text/html;charset=gb2312">
<style type="text/css">
.hidden{display:none;}
#smallLay{width:498px; height:100px;padding:4px 10px 10px;background-color:#FFFFFF;border:1px solid #05549d;color:#333333;line-height:24px;text-align:left;-webkit-box-shadow:5px 2px 6px #000;-moz-box-shadow:3px 3px 6px #555;}
</style>
<script type="text/javascript">
function showid(idname){
var isIE = (document.all) ? true : false;
var isIE6 = isIE && ([/MSIE (\d)\.0/i.exec(navigator.userAgent)][0][1] == 6);
var newbox=document.getElementById(idname);
newbox.style.zIndex="9999";
newbox.style.display="block"
newbox.style.position = !isIE6 ? "fixed" : "absolute";
newbox.style.top =newbox.style.left = "50%";
newbox.style.marginTop = - newbox.offsetHeight / 2 + "px";
newbox.style.marginLeft = - newbox.offsetWidth / 2 + "px";
var layer=document.createElement("div");
layer.id="layer";
layer.style.width=layer.style.height="100%";
layer.style.position= !isIE6 ? "fixed" : "absolute";
layer.style.top=layer.style.left=0;
layer.style.backgroundColor="#000";
layer.style.zIndex="9998";
layer.style.opacity="0.6";
document.body.appendChild(layer);
var sel=document.getElementsByTagName("select");
for(var i=0;i<sel.length;i++){
sel[i].style.visibility="hidden";
}
function layer_iestyle(){
layer.style.width=Math.max(document.documentElement.scrollWidth, document.documentElement.clientWidth)
+ "px";
layer.style.height= Math.max(document.documentElement.scrollHeight, document.documentElement.clientHeight) +
"px";
}
function newbox_iestyle(){
newbox.style.marginTop = document.documentElement.scrollTop - newbox.offsetHeight / 2 + "px";
newbox.style.marginLeft = document.documentElement.scrollLeft - newbox.offsetWidth / 2 + "px";
}
if(isIE){layer.style.filter ="alpha(opacity=60)";}
if(isIE6){
layer_iestyle()
newbox_iestyle();
window.attachEvent("onscroll",function(){
newbox_iestyle();
})
window.attachEvent("onresize",layer_iestyle)
}
layer.onclick=function(){newbox.style.display="none";layer.style.display="none";for(var i=0;i<sel.length;i++){
sel[i].style.visibility="visible";
}}
}
</script>
</head>
<body>
<input type="button" id="showbtn" name="showbtn" value="点我弹出层" onclick="showid('smallLay');">
<div id="smallLay" style="display:none;"></div>
</body>
</html>
代码参考自http://www.codefans.net/jscss/code/2312.shtml 经试验帮了我忙，抄下来，备忘
