jQuery之jsonp 跨域访问

Javascript代码

$.ajax({

       url: "fromcar.ashx?methodName=toCart&callback=?",
          contentType: "application/json;charset=utf-8",
            type: "get",dataType: "jsonp", jsonp: "callback", 
            success: function(result) {     //回调函数，result，返回值"
             result=result.msg;
              
               
            },
            error:function(XMLHttpRequest, textStatus, errorThrown){
                alert("...");
            }
        });
        
        }
     });    

C#代码

if (context.Request.Params["callback"] != null)
                     {
                         string callback = context.Request.Params["callback"];
                         strMange = callback + "({\"msg\":\"返回内容\"})";
                     }