java script级联下拉列表框,JavaScript

<html>
<script language = "JavaScript">
var onecount;
subcat = new Array();
subcat[0] = new Array("20","232","abc");
subcat[1] = new Array("20","111","efg");
onecount=2;
function changelocation(locationid)
   {
    document.myform.SmallClassName.length = 1;
    var i;
    for (i=0;i < onecount; i++)
        {
            if (subcat[i][0] == locationid)
            {
                document.myform.SmallClassName.options[document.myform.SmallClassName.length] = new Option(subcat[i][0]

+"|"+subcat[i][2], subcat[i][0] +"|"+subcat[i][2]);
            }
        }
    }
</script>
<body><br />
<form id="myform" name="myform" method="post" action="">
<table width="98%" border="0" align="center" cellpadding="0" cellspacing="0">
     <tr>
<td height="43" colspan="2">
  <table width="100%" border="0" cellspacing="0" cellpadding="0">
                <tr>
                  <td width="26%" height="29">所属类别:</td>
                  <td width="74%" height="29">
    <select name="BigClassName" onChange="changelocation(this.value)" size="1">
                        <option selected value="19">项链|xianglian</option>
                                <option selected value="20">耳环|erhuan</option>
                                <option selected value="21">手镯|shouzhuo</option>
                         </select>
    <select name="SmallClassName">
                      <option value="" selected>不指定小类</option>
                         </select></td>
              </tr>
                </table>
        </td>
     </tr>
</table>
</form>
</body>
</html>