想大家都做过遮罩层这种常见的功能，css或jquery实现，实现方式多样化，这里http://我介绍我在项目中实现的方式，全屏遮罩，部分区域可操作，非常实用。
效果如下图： 
js 实现部分：
复制代码 代码如下:
<script type="text/javascript">
var myAlert = document.getElementById("alert");
var reg = document.getElementById("content").getElementsByTagName("a")[0];
reg.onclick = function() {
myAlert.style.background = "#e2ecf5";
myAlert.style.zIndex = "501";
myAlert.style.position = "absolute";
var signSpan = document.getElementById("signSpanId");
myAlert.style.top = signSpan.offsetTop;
myAlert.style.left = signSpan.offsetLeft;
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";
}
</script>
页面代码：
复制代码 代码如下:
<!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=gb2312" />
</head>
<body>
<table border="1" align="center" width="700px">
<tr>
<td width="300px" height="200px" style="font-size:28px; font-weight:bold">
<div id="content">
<a href="#">
启动遮罩层
</a>
</div>
</td>
<td style="vertical-align:top">
<div id="signSpanId" style="position:absolute;"></div>
<div id="alert" align="top">
<h4>
<span>
这是高亮显示区域
</span>
</h4>
<p>
<label>
用户名
</label>
<input type="text" />
</p>
<p>
<label>
密 码
</label>
<input type="password" />
</p>
<p>
<input type="submit" value="注册" />
<input type="reset" value="重置" />
</p>
</div>
</td>
<td width="100px">
<div>我是第三列</div>
</td>
</tr>
</table>
</body>
</html>