usePromise.js

function usePromise(createPromise) {
  const [error, setError] = useState()
  const [value, setValue] = useState()

  useEffect(() => {
    let current = true

    createPromise().then(
      value => {
        if (current) setValue(value)
      },
      error => {
        if (current) setError(error)
      }
    )

    return () => {
      current = false
    }
  }, [createPromise])

  return [error, value]
}

// Use it like this:

function Profile({ uid }) {
  const [error, user] = usePromise(useCallback(() => fetchUser(uid), [uid]))
  // ...
}