如何用JS实现下拉框中的值树形展示

主要的思路：
将全部记录读出，在后台重组读出的Datatable，用JS绑定。
示例：
js代码

//设置用户控件中的存放附件的文件路径的下拉框中的值  
SubModule_PMS_ProjTask_TaskAdd.SetUploadPath(proname.value,0,SetUploadPathDll);

c#后台代码

#region 设置附件存放位置的下拉框中的值 add by shirlly 20100112
    [AjaxPro.AjaxMethod]
    public DataTable SetUploadPath(string str, int pProjFolderID)
    {
        DataSet ds = null; 
        if (!Equals("", str))
        {
            int projectID = Int32.Parse(str); 
            SMSIPMS.BLL.PMS_ProjFolderInfo ProFolderBll = new SMSIPMS.BLL.PMS_ProjFolderInfo();
            ds = ProFolderBll.GetList(" ProjectID=" + projectID);
            DataTable inDatatable = ds.Tables[0];
            DataTable outDatatable = new DataTable();
            outDatatable.Columns.Add("ProjFolderID", typeof(System.Int32));
            outDatatable.Columns.Add("ProjFolderName", typeof(System.String));
            PMS.PMSCommon.addProFoloderOtherDll("", 0, inDatatable, 1, ref outDatatable);
            return outDatatable;
        }
        else
        {
            return null;
        }

    }
    #endregion

主要展示树形的代码：

#region 构造树形结构的DataTable  add by shirlly 20100113
        /// <summary>
        /// 构造树形结构的DataTable
        /// </summary>
        /// <param name="Pading"></param>
        /// <param name="DirId"></param>
        /// <param name="inDatatable">构造之前的DataTable</param>
        /// <param name="deep"></param>
        /// <param name="outDatatable">构造之后的DataTable</param>
        public static void addProFoloderOtherDll(string Pading, int DirId, DataTable inDatatable, int deep, ref DataTable outDatatable)
        {
            DataRow[] rowlist = inDatatable.Select("PProjFolderID='" + DirId + "'");
            foreach (DataRow row in rowlist)
            {
                string strPading = "";
                for (int j = 0; j < deep; j++)
                {
                    strPading += "　";         //用全角的空格
                }
                //添加节点
                string Note = strPading + "|--" + row["ProjFolderName"].ToString();
                DataRow dr = outDatatable.NewRow();
                dr[0] = row["ProjFolderID"].ToString();
                dr[1] = Note;
                outDatatable.Rows.Add(dr);

                //递归调用addOtherDll函数，在函数中把deep加1
                addProFoloderOtherDll(strPading, Convert.ToInt32(row["ProjFolderID"].ToString()), inDatatable, deep + 1, ref outDatatable);
            }
        } 
        #endregion

JS代码：

//设置用户控件的下拉框中的值
        function SetUploadPathDll(response)
        {
            var dt = response.value;
            document.getElementById("MyUpdateFile_dropFileClass").options.length = 0; //通过用户控件ID+用户控件中想获得控件的ID
            var UploadPathDll = document.getElementById("MyUpdateFile_dropFileClass");
            UploadPathDll.options.add(new Option("--请选择--", ""));
            if (dt != null)
            {  
                for (var i = 0; i < dt.Rows.length; i++)
                {
                    var UploadPathDll_text = dt.Rows[i]["ProjFolderName"];
                    var UploadPathDll_value = dt.Rows[i]["ProjFolderID"];
                    UploadPathDll.options.add(new Option(UploadPathDll_text, UploadPathDll_value)); 
                }
            }
        }