I did this as a warm-up to using [React hooks](https://reactjs.org/docs/hooks-intro.html), which provide a better way to accomplish stateful things and side effects using functional components. This allows all components to be written in the same style, improves testability, facilitates code reuse, etc.
There's [a intro here](https://reactjs.org/docs/hooks-intro.html) which links to [Dan's talk at React Conf](https://www.youtube.com/watch?time_continue=3599&v=dpw9EHDh2bM) which does a really good job of explaining why hooks are a good way to write components. He describes hooks as being the electrons and neutrons to components which are atoms. Low-level functionality which was always there in React, though not as accessibly or visibly.
This adds a lint rule that enforces "the rule of hooks" which says they have to be declared at the top level in the functional component.
I don't think this changeset does a fabulous job of showing off the improvements hooks allows, though I think it is still a good direction for this code.
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