Questions and answers

Here are some questions and answers to refresh your knowledge:

1. What is a state?

   For a function component, a state is a value created to be persistent during the life of the component. From each update, including the mount, this value can be accessed from inside a function.

2. What are the usages of states?

   If a task can't be done within one update, that is the time we can think of using a state to reference a memory that can be accessed in multiple updates. We normally use a state to request a new update, listen to a value change, as well as perform a task at the mount. But the states can be very versatile.

3. What does a state do to the UI?

   To determine the screen corresponding to a component, we need to know its states as well as its props. While the props are passively defined on the component interface, the states are defined inside the component to actively refine its behavior. Apps built with states can change with time, driven by either user interactions or any other external processes.