Cacher is the code snippet organizer for pro developers

A React component should use props to store information that can be changed, but can only be changed by a different component.

A React component should use state to store information that the component itself can change.

The main purpose of componentWillUpdate is to interact with things outside of the React architecture. If you need to do non-React setup before a component renders, such as checking the window size or interacting with an API, then componentWillUpdate is a good place to do that.