Reading 28 Props and State - liz-kavalski-401-advanced-javascript/seattle-javascript-401n13 GitHub Wiki
Understanding React setState
State can be anything
React components with state render UI based on that state, if the state change so does the UI
setState() is the only legitimate way to update state after the initial state setup.
The reconciliation process is the way React updates the DOM, by making changes to the component based on the change in state.
Functional vs class components
A functional component is just a plain JavaScript function which accepts props as an argument and returns a React element.
A class component requires you to extend from React.Component and create a render function which returns a React element.
requires more code.
If you need a state in your component you will either need to create a class component or you lift the state up to the parent component and pass it down the functional component via props.
Use functional components if you are writing a presentational component which doesn’t have its own state or needs to access a lifecycle hook.