js简单遮罩效果(可解决select)
实现效果：弹出一个窗口的时候，窗口后面的页面变暗，并且不能操作

难点：因为div层是不能把select控件遮住的，所以要特殊处理，方法两种，一种是在弹出窗口下面加一层iframe来遮住select；第二种是所以要在弹出的时候，先把select控件隐藏，这里选择第二种方法

实现原理：在页面上和弹出窗口中间加一个半透明的层，把页面的内容覆盖掉

主要代码：
<script language="javascript">
function Open()
{
  //隐藏select控件
  DispalySelect(0); 
  //显示遮罩层
  document.getElementById("divPageMask").style.display="block";
//处理遮罩层
  resizeMask();
window.onResize = resizeMask;
  //显示弹出窗口
  document.getElementById("divOpenWin").style.display="block";
}
function Close()
{
  //显示select控件
  DispalySelect(1);
  //处理遮罩层
  divPageMask.style.width = "0px";
divPageMask.style.height = "0px";
divOpenWin.style.display = "none";
window.onResize = null;
 
  document.getElementById("divOpenWin").style.display="none";
}
//页面遮罩
function resizeMask()
{
divPageMask.style.width = document.body.scrollWidth;
divPageMask.style.height = document.body.scrollHeight;
divOpenWin.style.left = ((document.body.offsetWidth - divOpenWin.offsetWidth) / 2);
divOpenWin.style.top = ((document.body.offsetHeight - divOpenWin.offsetHeight) / 2);
}
function DispalySelect(val)
{  //显示和隐藏select控件
var dispalyType;
  var arrdispalyType=["hidden","visible"];
  var arrObjSelect=document.getElementsByTagName("select");
  for (i=0;i<arrObjSelect.length;i++)
  {
    arrObjSelect[i].style.visibility=arrdispalyType[val];
  }
}
</script>





下面是HTML例子

<style type="text/css">
.body,td{font-size:12px}
#divPageMask{background-color:white; filter:alpha(opacity=50);left:0px;position:absolute;top:0px;}
#divOpenWin{background-color:#EEEEEE;position: absolute;left:0px;top:0px;display: none;z-index:50; width:300px;height:150px}
</style>

<div id="divPageMask"></div>//遮罩层
<div id="divOpenWin"><center><a href="javascript:Close();">关闭</a></center></div>//弹出层
<label></label>
<center>
 <table border="0" cellpadding="0" cellspacing="0" width="650">
 <tbody>
 <tr>
 <td colspan="2" align="center" height="90"><p><img src="http://www.sopull.com/Images/Index/logo.gif" height="60" width="250"></p>
 <p>&nbsp;</p>
 <p>&nbsp;</p></td>
 </tr>
 <tr>
 <td height="10" style="color:#666666;font-size:13px">&nbsp;</td>
 </tr>
 </tbody>
 </table>
 </center>
<select><option>1<option>
<option>11<option>
<option>11<option>
</select>
<p align="center">&nbsp;</p>
<p align="center"><a href="javascript:Open();">打开遮罩</a></p>

 </tbody>
</table>