export function useSubscription()

in src/devtools/views/hooks.js [145:204]

• 39 lines of code
• 5 McCabe index (conditional complexity)

export function useSubscription<Value>({
  getCurrentValue,
  subscribe,
}: {|
  getCurrentValue: () => Value,
  subscribe: (callback: Function) => () => void,
|}): Value {
  const [state, setState] = useState({
    getCurrentValue,
    subscribe,
    value: getCurrentValue(),
  });

  if (
    state.getCurrentValue !== getCurrentValue ||
    state.subscribe !== subscribe
  ) {
    setState({
      getCurrentValue,
      subscribe,
      value: getCurrentValue(),
    });
  }

  useEffect(() => {
    let didUnsubscribe = false;

    const checkForUpdates = () => {
      if (didUnsubscribe) {
        return;
      }

      setState(prevState => {
        if (
          prevState.getCurrentValue !== getCurrentValue ||
          prevState.subscribe !== subscribe
        ) {
          return prevState;
        }

        const value = getCurrentValue();
        if (prevState.value === value) {
          return prevState;
        }

        return { ...prevState, value };
      });
    };
    const unsubscribe = subscribe(checkForUpdates);

    checkForUpdates();

    return () => {
      didUnsubscribe = true;
      unsubscribe();
    };
  }, [getCurrentValue, subscribe]);

  return state.value;
}