Jquery简单的遮罩层

本人Js菜鸟，最近要用到遮罩层

从网上找到一个大神的代码，备份一下

<html xmlns="http://www.w3.org/1999/xhtml">
<head>
    <title></title>
    <script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.6.1/jquery.min.js"></script>
    <script type="text/javascript">
        $(function () {
            $("#layer")
                .height($(document).height())
                .width($(document).width()).hide();
            $("#btn").click(function () {
                $("#layer").show();
            });
            $("#layer").click(function () {
                $(this).hide();
            });
        });
    </script>
    <style type="text/css">
        #layer{ position: absolute;top: 0;left: 0;opacity: 0.6; background-color:#000000; z-index:999;}
    </style>
</head>
<body>
    <div id="layer"></div>
    <input type="button" id="btn" />
</body>
</html>