重写jquery的ajax方法

    //首先备份下jquery的ajax方法
    var _ajax=$.ajax;  

    //重写jquery的ajax方法
    $.ajax=function(opt){
        //备份opt中error和success方法
        var fn = {
            error:function(XMLHttpRequest, textStatus, errorThrown){},
            success:function(data, textStatus){}
        }
        if(opt.error){
            fn.error=opt.error;
        }
        if(opt.success){
            fn.success=opt.success;
        }  

        //扩展增强处理
        var _opt = $.extend(opt,{
            error:function(XMLHttpRequest, textStatus, errorThrown){
            debugger;
                erro = eval("(" + XMLHttpRequest.responseText + ")");
                if(erro.err_code == 500)
                    alert(erro.err_msg);
                //错误方法增强处理
                fn.error(XMLHttpRequest, textStatus, errorThrown);
            },
            success:function(data, textStatus){
                //成功回调方法增强处理
                fn.success(data, textStatus);
            },
            beforeSend:function(xhr){
                xhr.setRequestHeader('X-Token',$.getCookie("X-Token"));
                 xhr.setRequestHeader('X-Client',"PC");
                xhr.setRequestHeader('Content-Type',"application/json");
            }
        });
        return _ajax(_opt);
    };