A quick React gist of a clock.

Clock.js

function clock(){
  const tick = (
    <div>
      <h1>The Time is:</h1>
      <h2>time: {new Date().toLocaleTimeString()}</h2>
    </div>
  );
  ReactDOM.render(
    tick,
    document.getElementById('root')
  );
}
setInterval(clock, 1000);