带半透明遮罩背景层的js点击弹出登录框代码【原创】

js代码

<script type="text/javascript"> 
var myAlert = document.getElementById("alert"); 
var reg = document.getElementById("content").getElementsByTagName("a")[0]; 
var mClose = document.getElementById("close"); 
reg.onclick = function() 
{ 
myAlert.style.display = "block"; 
myAlert.style.position = "absolute"; 
myAlert.style.top = "50%"; 
myAlert.style.left = "50%"; 
myAlert.style.marginTop = "-75px"; 
myAlert.style.marginLeft = "-150px";

mybg = document.createElement("div"); 
mybg.setAttribute("id","mybg"); 
mybg.style.background = "#000"; 
mybg.style.width = "100%"; 
mybg.style.height = "100%"; 
mybg.style.position = "absolute"; 
mybg.style.top = "0"; 
mybg.style.left = "0"; 
mybg.style.zIndex = "500"; 
mybg.style.opacity = "0.3"; 
mybg.style.filter = "Alpha(opacity=30)"; 
document.body.appendChild(mybg);

document.body.style.overflow = "hidden"; 
}

mClose.onclick = function() 
{ 
myAlert.style.display = "none"; 
mybg.style.display = "none"; 
} 
</script>