:hidden：表示查询所有隐蔽的标签
:visible：表示查询所有显示的标签
或:not(:hidden)
<html> <head> <meta http-equiv="content-type" content="text/html; charset=UTF-8"> <script type="text/javascript" src="../js/jquery-1.6.js"></script> </head> <body> <table border="1" align="center"> <tr > <td>Value 1</td> </tr> <tr> <td>Value 2</td> </tr> <tr> <td>Value 3</td> </tr> </table> <script type="text/javascript"> //1)查找隐藏的tr元素的个数 //alert($("table tr:hidden").size()); //alert($("tr:hidden").size()); //2)查找所有可见的tr元素的个数 //alert($("table tr:visible").size()); //alert($("table tr:not(:hidden)").size()); </script> </body></html>