判断div是否隐藏

<script type="text/javascript" src="../js/jquery-1.7.2.min.js"></script>
<script language="javascript">
function beg()
{
var a=$("#bei").css(\'display\');
b="none"
if(a==b)
{
$("#bei").css(\'display\',\'block\');
}
else
{
$("#bei").css(\'display\',\'none\');
}
}
</script>