Playground

Live Editor

function Clock(props) {
    const [date, setDate] = useState(new Date());
    useEffect(() => {
        const timerID = setInterval(() => tick(), 1000);

        return function cleanup() {
            clearInterval(timerID);
        };
    });

    function tick() {
        setDate(new Date());
    }

    return (
        <div>
            <h2>It is {date.toLocaleTimeString()}.</h2>
        </div>
    );
}

Result

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