class HelloWorld extends React.Component<{date: Date}, void> {
  render() {
    return (
      <p>
        Hello, <input type="text" placeholder="Your name here" />!
        It is {this.props.date.toTimeString()}
      </p>
    );
  }
}

setInterval(function() {
  ReactDOM.render(
    <HelloWorld date={new Date()} />,
    document.getElementById('example')
  );
}, 500);