preact use hook

use.ts

function use<T>(promiseOrContext: Promise<T> | Context<T>): T {
  if ('__c' in promiseOrContext) {
    return useContext(promiseOrContext)
  }

  return usePromise(promiseOrContext)
}

function usePromise<T>(promise: Promise<T>): T {
  const resolving = useRef(false);
  const pending = useRef(promise);
  const unmounted = useRef(false);
  const [value, setValue] = useState(null);
  const [error, setError] = useState(null);

  if (error !== null) {
    throw error;
  }

  if (!resolving.current) {
    resolving.current = true;
    pending.current.then(
      (value) => {
        if (unmounted.current) return;
        setValue(value);
      },
      (err) => {
        if (unmounted.current) return;
        setError(err);
      }
    );
  }

  useEffect(() => {
    return () => {
      unmounted.current = true;
    };
  }, []);

  if (!resolved.current) {
    throw pending.current;
  }

  return value;
}