js 简单的三级菜单

<form name="frm">
<select name="s1" onChange="redirec(document.frm.s1.options.selectedIndex)">
<option selected>请选择</option>
<option value="1">脚本语言</option>
<option value="2">高级语言</option>
<option value="3">其他语言</option>
</select>

<select name="s2">
<option value="请选择" selected>请选择</option>
</select>
</form>

<script language="javascript">
//获取一级菜单长度
var select1_len = document.frm.s1.options.length;
var select2 = new Array(select1_len);

//把一级菜单都设为数组
for (i=0; i<select1_len; i++)
{
select2[i] = new Array();
}

//定义基本选项
select2[0][0] = new Option("请选择", " ");

select2[1][0] = new Option("PHP", " ");
select2[1][1] = new Option("ASP", " ");
select2[1][2] = new Option("JSP", " ");

select2[2][0] = new Option("C/C++", " ");
select2[2][1] = new Option("Java", " ");
select2[2][2] = new Option("C#", " ");

select2[3][0] = new Option("Perl", " ");
select2[3][1] = new Option("Ruby", " ");
select2[3][2] = new Option("Python", " ");

//联动函数
function redirec(x)
{
var temp = document.frm.s2;
for (i=0;i<select2[x].length;i++)
{
temp.options[i]=new Option(select2[x][i].text,select2[x][i].value);
}
temp.options[0].selected=true;

}

</script>