菜鸟求助，怎么做一个选择级联，

<html>
<title>考试申请</title>
<head>
<script type="text/javascript"> var termlist=new Array();
  termlist['第一学期']=["c#","计算机基础","电子商务概论",];
 termlist['第二学期']=["dreameaver","市场营销","网络","asp",];
function changeterm()
{
  var term=document.getElementById("selterm").value;
  var class=document.getElementById("selclass");
  class.options.length=0;
   for(var i in termlist)
       {
     if (i==term)
    {
for(var j in termlist[i]) 
                                  class.add(new option(termlist[i][j],null))
                                  

 }
   }
  
}</script>
</head>
<body>
<select id="selterm" onChange="changeterm()" style="width:100px">
<option>选择学期</option></select>
<select id="selclass" style="width:100px">
<option>选择课程</option>
</select>
</body>
</html>

解决方案 »

  1.   


    <html>
    <title>考试申请</title>
    <head></head>
    <body>
    <select id="selterm" onChange="changeterm()" style="width:100px">
    <option>选择学期</option></select>
    <select id="selclass" style="width:100px">
    <option>选择课程</option>
    </select>
    <script type="text/javascript"> var termlist = [];
    termlist['第一学期'] = ["c#","计算机基础","电子商务概论"];
    termlist['第二学期'] = ["dreameaver","市场营销","网络","asp"];
    var tmp = [];
    var obj1 = document.getElementById('selterm');
    var obj2 = document.getElementById('selclass');
    for(var x in termlist){
    obj1.add(new Option(x, null));
    tmp.push(x);
    }
    function changeterm(){
    var l = termlist[tmp[obj1.selectedIndex - 1]];
    obj2.length = 1;
    for(var i = 0, len = l.length; i< len; i++){
    obj2.add(new Option(l[i], null));
    }
    }



    </script></body>
    </html>
    试试
      

  2.   

    <html>
    <title>考试申请</title>
    <head>
    <script type="text/javascript">
    var termlist = new Array();
    termlist['第一学期'] = ["c#","计算机基础","电子商务概论"];
    termlist['第二学期'] = ["dreameaver","市场营销","网络","asp"];
    function changeterm() {
    var term = document.getElementById('selterm').value;
    var cls = document.getElementById('selclass'); //class是Javascript语言保留字，不能用作变量名
    cls.options.length = 0;
    for (var i in termlist) {
    if (i == term) {
    for(var j in termlist[i]) cls.options.add(new Option(termlist[i][j], termlist[i][j]));
    }
    }
    }
    window.onload = function() {
    var obj = document.getElementById('selterm');
    for(var i in termlist) obj.options.add(new Option(i, i));
    }
    </script>
    </head>
    <body>
    <select id="selterm" onChange="changeterm()" style="width:100px">
      <option>选择学期</option>
    </select>
    <select id="selclass" style="width:100px">
      <option>选择课程</option>
    </select>
    </body>
    </html>