二级连动的另一个不错的实现方法

<table width="400" border="1" cellspacing="0" cellpadding="0" align="center" bordercolordark="#9cc384" bordercolorlight="#ffffff"><tr bgcolor="#e6f0dd" align="center"> <td> <form method="post" action="a_list.asp" name="send" target="_blank"> <table width="62%" border="0" cellspacing="2" cellpadding="2"><tr> <td width="44%" align="right">类别：</td> <td width="56%"> <table width="95%" border="0" cellspacing="0" cellpadding="0"> <tr> <td> <select name="class0" onchange="onselectchange()"><option value="2">** 选择一级类别 ** </option> <option value="0">a </option> <option value="1">b </option></select> </td> </tr> <tr> <td> </td> </tr> <tr> <td> <select name="class1"><option value="1">** 选择二级类别 ** </option></select> </td> </tr> </table> </td> </tr></table> </form> </td> </tr></table>
[ctrl+a 全选 注:如需引入外部js需刷新才能执行]