The components of Vue are reusable. After a component is created, it can be reused in multiple places, no matter how many times it is reused, the
dataThey should be isolated from each other, so every time a component is reused,
dataIt should be reused once, every time
dataThe change should have no effect on the data of other reusable components.
In order to achieve this effect,
dataIt can not be a simple object, but in the form of a function return value, so each component instance can maintain an independent copy of data without mutual influence.