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Wrong usage of useEffect in custom hook docs #4369

Description

@arn4v

The Building Your Own Hooks page suggests invoking the useEffect hook without passing in an empty dependency array

function useFriendStatus(friendID) {
  const [isOnline, setIsOnline] = useState(null);

  useEffect(() => {
    function handleStatusChange(status) {
      setIsOnline(status.isOnline);
    }

    ChatAPI.subscribeToFriendStatus(friendID, handleStatusChange);
    return () => {
      ChatAPI.unsubscribeFromFriendStatus(friendID, handleStatusChange);
    };
  });

  return isOnline;
}

As there is no dependency array passed to useEffect, this would cause multiple multiple un/subscribe API calls. Shouldn't the example snippet have an empty dependency array?

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