/**
 * Hook that returns a function that tells if the component is currently mounted.
 * Useful to avoid calling setState on unmounted components after async actions.
 *
 * @example
 * const isMounted = useIsMounted();
 * useEffect(() => {
 *   fetchData().then((res) => {
 *     if (isMounted()) setState(res);
 *   });
 * }, []);
 *
 * @returns A function returning boolean: true if mounted, false otherwise.
 */
export declare function useIsMounted(): () => boolean;