public class DropDownListJson : IHttpHandler
    {

        public void ProcessRequest(HttpContext context)
        {
            if (context.Request["CodeType"] == "EnterpriseType")
            {
                UnitType(context);
            }
        }

        private void UnitType(HttpContext context)
        {
            List<T_UnitTypeInfo> list = new T_UnitTypeDAL().GetAll();
            string result=JsonHelper.GetJson<List<T_UnitTypeInfo>>(list);
            context.Response.ContentType = "application/json";
            context.Response.Write(result);
            context.Response.End();
        }
        public bool IsReusable
        {
            get
            {
                return false;
            }
        }
    }
 

  function iniEnterpriseType() {
            $.ajax({
                type: 'GET',
                url: '../../Ajax/DropDownListJson.ashx?CodeType=EnterpriseType',
                dataType: 'json',
                async: false,
                timeout: 2000,
                success: function (data) {
                    for (var i = 0; i < data.length; i++) {
                        $("#AreaSelect").append("<option value='" + data[i].UnitType + "'>" + data[i].UnitTypeName + "</option>");
                    };
                    $("#AreaSelect").append("<option value='0'  selected='selected'>全部</option>");
                    //document.getElementById('AreaSelect').value = "a";
                },
                error: function (XMLHttpRequest, textStatus, errorThrown) {
                    alert("獲取機構型別資料失敗！");
                }
            })
        }
 

  機構型別：
                <select class="selector" id="AreaSelect" style="width:170px;height:24px;line-height:24px;border: 1px solid #BBBBBB;">
                </select>