react.dev/examples/rendering-elements/update-rendered-element.js

function tick() {
  const element = (
    <div>
      <h1>Hello, world!</h1>
      <h2>
        It is{' '}
        {new Date().toLocaleTimeString()}.
      </h2>
    </div>
  );
  ReactDOM.render(
    element,
    document.getElementById('root')
  );
}

setInterval(tick, 1000);