laravel 5.5 ajax返回错误信息

前段ajax发送请求 

$('#reg_reg').click(function () {
        var formData = new FormData($( "#reg_form" )[0]);
        var url = "{{ url('/admin/register') }}";

        $.ajax({
            headers: {
                'X-CSRF-TOKEN': $('meta[name="csrf-token"]').attr('content')
            },
            url: url,
            type: 'POST',
            data: formData,
            cache: false,
            contentType: false,
            processData: false,
            success: function(res){
                console.log(res);
                // if(res.code){
                //     redirect_success(res.msg, res.url)
                // }else{
                //     error(res.msg);
                // }
            },
            error : function (msg ) {
                var json=JSON.parse(msg.responseText);
                $.each(json.errors, function(idx, obj) {
                    alert(obj[0]);
                    return false;
                });
            },
        })
    })

 

laravel 创建验证的 表单请求（ form request ）  执行命令 php artisan make:request StoreBlogPostRequest