function Clock(props) {
const [date, setDate] = useState(new Date());
useEffect(() => {
var timerID = setInterval(() => tick(), 1000);
return function cleanup() {
clearInterval(timerID);
};
});
function tick() {
setDate(new Date());
}
return (
<div>
<h1>Hello, world!</h1>
<h2>It is {date.toLocaleTimeString()}.</h2>
</div>
);
}