Three stages: creation stage --- operation stage --- destruction stage
1. Creation stage
（1）beforeCreate
(2) created (commonly used in actual projects): the props/data/methods of the component have been created, and when entering this page, the component can call the method and get the data
（3）beforeMount
(4) mounted (commonly used in actual projects): the html in the memory has been rendered into the browser, and the DOM structure can be manipulated
2. Operation stage
（1）beforeUpdate
(2) updated (commonly used in actual projects): when the data changes, in order to operate the latest DOM structure, the code needs to be written here
3. Destruction stage
（1）beforeDestroy
(2) destroyed (commonly used in actual projects): destroy components and remove DOM structure
