checkbox实现全选

<%@ page contentType="text/html;charset=gbk" %>
<form name="frm" method="post" action="">
   <table class="ItemList" width="99%" align="center">
   <tr align="center">
     <td width="3%" nowrap>全选本页
         <input type="checkbox" name="allCheck" onclick="javascript:selectAll();">
        </td>
   </tr>
   
   <%
     for(int i = 0;i < resultInfos.length;i++){
      QueryPrintResultInfo info = (QueryPrintResultInfo)resultInfos[i];
   %>
   <tr>
     <td nowrap><input type="checkbox" name="printCheck" value="<%=info.getID()%>"></td>
   </tr>
   <%
     }
   %>
 </table>
</form>

<script language="javascript">
   function selectAll()
 { 
  if (isNaN(frm.printCheck.length))
  {
   if ( frm.allCheck.checked == true )
   {
    frm.printCheck.checked = true;
   }
   else {
    frm.printCheck.checked = false;
   }
  }
  else {
   if(frmV002.allCheck.checked == true)
   {
    for(var i = 0;i < frmV002.printCheck.length;i++)
    {
     frm.printCheck[i].checked = true;
    }
   }
   else
   {
    for(var i = 0;i < frmV002.printCheck.length;i++)
    {
     frm.printCheck[i].checked = false;
    }
   }
  }
 }
</script>