php模板中的select控件的onchang事件代码不起作用

php模板中的select控件的onchang事件代码不起作用,如下：
<script language="JavaScript">
  function s_changed()  //cjq add
  {
         alert("s_changed");
                 var index=document.forms['theForm'].s[].selectedIndex;
         if ((document.forms['theForm'].s[].options[index].value=='2')
                 {
                   alert("ok");
                    ...
                 }
  }
</script>
 
<form name="theForm" action="o.php?act=s" method="post">
<table>
  <tr>
    <td scope="col">1</td>
    <td scope="col">2</td>
  </tr>
  {foreach from=$g1 item=g name="g"}
    <tr>
    <td>1</td>
    <td><select name="s[]" onchange="JavaScript:s_changed()">
      <option value=" ">请选择</option>
      {foreach from=$s1_list item=s}
           <option value="{$s.name}" {if $s.name eq  $s1}selected{/if}>{$s.name}</option>
      {/foreach}
      {/if}
    </select>   
    </td>
    </tr>
{/foreach}
</table>
</form>

请问这是为什么？