Esimerkit sovellettu tai lainattu seuraavista lähteistä:
- https://github.com/codento/react-workshop
- https://fullstack-hy2019.github.io/osa5/custom_hookit
- https://medium.com/simply/state-management-with-react-hooks-and-context-api-at-10-lines-of-code-baf6be8302c
- Ent. componentWillUnmount