Property or method “toJSON“ is not defined on the instance but referenced during render.

Property or method “toJSON” is not defined on the instance but referenced during render. Make sure that this property is reactive, either in the data option, or for class-based components, by initializing the property.
翻译：属性或方法“toJSON”未在实例上定义，但在呈现过程中被引用。通过初始化属性，确保此属性是被动的，无论是在data选项中，还是对于基于类的组件。参见：https://vuejs.org/v2/guide/reactivity.html声明-反应特性。

解决方案：在vue的实例methods里面定义一个toJSON(){}函数即可解决