请问怎么用JavaScript给select中的项赋值呢？？？不懂我哪里错了...

<form name = "edit">
       <select name="class2" id="mySelect" size="1">
              <OPTION selected="selected">one</OPTION>
              <OPTION>two</OPTION>
              <OPTION>three</OPTION>
              <OPTION>four</OPTION>
      </select>
                    
</form>
                    
<script language=JavaScript>
                                            
        function changeSelect(){
        var obj=document.edit.class2.options[0]=new Option(request.QueryString(key),request.QueryString(key));
        }
                                          
</script>


原本是希望用从其他网页传递过来的参数去替换到select的第一项的。但是代码完全无效...

不知道究竟错在哪里了。知道的朋友帮我一下吧！谢谢了！