二级连动的另一个不错的实现方法

答案：
<script > 
<!-- 
function onselectchange(){ 
  num=document.send.class0.options[document.send.class0.selectedIndex].value; 
  switch(num){ 
     case "0": 
document.send.class1.options.length=4; 
document.send.class1.options[00].text="A1"; 
document.send.class1.options[00].value=0; 
document.send.class1.options[01].text="A2"; 
document.send.class1.options[01].value=1; 
document.send.class1.options[02].text="A3"; 
document.send.class1.options[02].value=2; 
document.send.class1.options[03].text="A4"; 
document.send.class1.options[03].value=3; 
break; 
case "1": 
document.send.class1.options.length=6; 
document.send.class1.options[00].text="B1"; 
document.send.class1.options[00].value=0; 
document.send.class1.options[01].text="B2"; 
document.send.class1.options[01].value=1; 
document.send.class1.options[02].text="B3"; 
document.send.class1.options[02].value=2; 
document.send.class1.options[03].text="B4"; 
document.send.class1.options[03].value=3; 
document.send.class1.options[04].text="B5"; 
document.send.class1.options[04].value=4; 
document.send.class1.options[05].text="B6"; 

break; 

  } 
} 
//--> 
</script> 



<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>

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