递归分类点击上级类别才显示出下级类别如何写 _ASP

递归分类点击上级类别才显示出下级类别怎么写？
id   mc   fid
1        珠心算      0
2        启蒙班      1
3        预备上      2
4        预备下      2

下面是列出分类的代码，请问要点击上级类别才显示出下级类别怎么写？而不是列出全部类别.如点击珠心算就显示出启蒙班，再点击一下珠心算就把启蒙班隐藏起来，同样的，点击启蒙班就显示出预备上和预备下，再点击一下启蒙班就隐藏预备上和预备下

<%
Function Echo(Str) '输出字符串并换行
    Response.Write Str &"<br />"
End Function

Dim MyCount
MyCount = 0

Sub SubFl(FID)
Dim Rs1,sql1,i
sql1="select * from km where fid = "&FID&" order by Id"'查询类别
Set Rs1=server.createobject("adodb.recordset")
Rs1.open sql1,conn,1,1
If Not Rs1.Eof Then
    MyCount = MyCount + 1 '流水号+1
    Do While Not Rs1.Eof
     For i = 1 to MyCount
     If i = 1 then
       Response.Write "+"
     Else
       Response.Write "----"
     End If
    Next
     Response.Write " "
     Echo(""&Rs1("mc"))
     Call SubFl(Trim(Rs1("Id"))) '递归子级分类
    Rs1.Movenext:Loop
    If MyCount <> 0 Then'如果这个类没有子分类就不需要减一
     MyCount = MyCount - 1'没有下级分类减1 继续查找上一级
    End If
    If Rs1.Eof Then
     Rs1.Close
     Exit Sub
    End If
End If
Set Rs1 = Nothing
End Sub

Sub MainClass()
sql="select * from km where fid = 0 order by Id"'主分类搜索
Set Rs=server.createobject("adodb.recordset")
Rs.open sql,conn,1,3
If Not Rs.Eof Then
    Do While Not Rs.Eof
    Echo(""&Rs("mc"))
    Call SubFl(Trim(Rs("Id"))) '递归子级分类
    Rs.Movenext:Loop
Else
    Response.Write "还没有分类"
End If
End Sub

Call MainClass()

%>

------解决方案--------------------

------解决方案--------------------
那个肯定是要通过JS操作的了