/**
 * Hook to store a state value for comparison in a useEffect hook.
 * e.G.
 *    ```
 *    const [value, setValue] = useState();
 *    const previousValue = usePrevious(value);
 *
 *    useEffect(() => {
 *      if(value.a !== previousValue.a) {
 *        // do something
 *      }
 *    }, []);
 *    ```
 *
 * @param value The variable value that should be stored.
 * @returns The previously stored variable value.
 */
export declare const usePrevious: <T extends unknown>(value: T) => T | undefined;