A userland React hook for managing global state

Yoav Kadosh shared a very useGlobalState React hook.

const store = {};
const listeners = {};

function useGlobalState(key, initialValue) {
  const [state, _setState] = useState(store[key] || initialValue);
  const setState = useCallback((stateOrSetter) => {
    let next = stateOrSetter;
    if (typeof stateOrSetter === "function") {
      next = stateOrSetter(store[key]);
    }

    listeners[key].forEach((l) => l(next));
    store[key] = next;
  }, []);
  useEffect(() => {
    // Store the initial state on the first call with this key
    if (!store[key]) {
      store[key] = initialValue;
    }
    // Create an empty array of listener on the first call with this key
    if (!listeners[key]) {
      listeners[key] = [];
    }
    // Register the observer
    const listener = (state) => _setState(state);
    listeners[key].push(listener);
    // Cleanup when unmounting
    return () => {
      const index = listeners[key].indexOf(listener);
      listeners[key].splice(index, 1);
    };
  }, []);
  return [state, setState];
}

You can then use the defined useGlobalState hook to share or update application state across components. 💪

const [state, setState] = useGlobalState('someUniqueKey', INITIAL_STATE);

Are there downsides to this pattern? I don't know, and I'm a little puzzled why I haven't seen this userland hook before, but if you think useGlobalState is a bad idea, let me know!

If you want to learn more, Yoav explains how it works on his blog!