function usePrevious(value) {
    const ref = useRef();

    useEffect(() => {
        ref.current = value;
    }, [value]);

    return ref.current;
}

function Counter() {
    const [count, setCount] = useState(0);
    const previousCount = usePrevious(count);

    return (
        <div>
            <p>Actuel : {count}</p>
            <p>Précédent : {previousCount}</p>
            <button onClick={() => setCount(c => c + 1)}>+1</button>
        </div>
    );
}