example.js

class Example extends React.Component {
  constructor(props) {
    super(props);
    this.state = {date: new Date()};
  }

  componentDidMount() {
    this.timerID = setInterval(
      () => this.tick(),
      1000
    );
  }

  componentWillUnmount() {
    clearInterval(this.timerID);
  }

  tick() {
    this.setState({
      date: new Date()
    });
  }

  render() {
    return (
      <div>
        <h1>Hello, world!</h1>
        <h2>
          <SuperEllipsis tailLength={9}>
            It is {this.state.date.toLocaleTimeString()}.
          </SuperEllipsis>
        </h2>
      </div>
    );
  }
}