笔记：

1、父子组件的加载顺序为：
父beforeCreated ->父created ->父beforeMounted ->子beforeCreated ->子created ->子beforeMounted ->子mounted -> 父mounted

2、父组件更新顺序为：
父beforeUpdate->父updated

3、子组件更新顺序为：
父beforeUpdate->子beforeUpdate->子updated->父updated

4、父子组件销毁顺序为：
父beforeDestroy->子beforeDestroy->子destroyed->父destroyed