js下拉框(select)联动

<form name="frm">
<select name="s1" size="1" onChange="redirec1(document.frm.s1.options.selectedIndex)">
 <option selected >浙江</option>
 <option >江苏</option>
</select>

<select name="s2" size="1" onChange="redirec2(document.frm.s1.options.selectedIndex,document.frm.s2.options.selectedIndex)">
 <option selected>杭州</option>
<option>金华</option>
</select>

<select name="s3" size="1">
 <option selected>富阳</option>
<option>萧山</option>
</select>
</form>
<script language="javascript">
var select2 = new Array(new Array(new Option("杭州"),new Option("金华")),new Array(new Option("苏州"),new Option("连云港")));
var select3 = new Array(new Array(new Array(new Option("富阳"),new Option("萧山")),new Array(new Option("永康"),new Option("义务"))),new Array(new Array(new Option("aa"),new Option("aaa"),new Option("aaaa"),new Option("aaaaa")),new Array(new Option("bb"),new Option("bbb"))));
function redirec1(x)
{
 var temp = document.frm.s2;
temp.length=0
 for (i=0;i<select2[x].length;i++)
 {
  temp.options[i]=new Option(select2[x][i].text);
 }
redirec2(document.frm.s1.options.selectedIndex,document.frm.s2.options.selectedIndex)

}

function redirec2(x,y)
{
 var temp = document.frm.s3;
temp.length=0
 for (i=0;i<select3[x][y].length;i++)
 {
  temp.options[i]=new Option(select3[x][y][i].text);
 }
}
</script>