下拉框赋值

function populateClass3()//Ajax执行成功的回调函数
{
    var f=document.getElementById("specialty");
    if(http_request.readyState==4)
    {
            if(http_request.status==200)
            {
                var list=http_request.responseText;
                var classList=list.split("|");
                f.options.length=1;
                for(var i=0;i<classList.length;i++)
                        //将取得的结果添加到下级的列表框中
                {
                    var tmp=classList[i].split(",");
                    f.add(new Option(tmp[1],tmp[0]));
                }
            }
            else
            {
                alert("您所请求的页面有异常。");
            }
    }
}