(function(){

window.Mask = {version:1.0};
var D=new Function('obj','return document.getElementById(obj);');
var oevent=new Function('e','if (!e) e = window.event;return e');

Mask.Login = function()
{
	$("mask").style.display = "block";
	$("mask").style.position = "absolute";
	$("mask").style.top = "0px";
	$("mask").style.left = "0px";
	//$("mask").style.width = "100%";
	//$("mask").style.height = document.documentElement.clientWidth + "px";//document.body.clientHeight + "px";
	$("mask").style.width = document.documentElement.scrollWidth + "px";
	$("mask").style.height = document.documentElement.scrollHeight + "px";//document.body.clientHeight + "px";
	$("mask").className = "b";
	$("mask").style.zIndex = "3";
	$("mask").style.filter = "alpha(opacity=40)";
	$("mask").style.opacity = "0.4";
	$("mask").style.backgroundColor = "#000000";
}

})();

页面调用只需要：

Mask.login();即可