1class Clock extends React.Component {
2  constructor(props) {
3    super(props);
4    this.state = {date: new Date()};
5  }
6
7  componentDidMount() {
8    this.timerID = setInterval(
9      () => this.tick(),
10      1000
11    );
12  }
13
14  componentWillUnmount() {
15    clearInterval(this.timerID);
16  }
17
18  tick() {    this.setState({      date: new Date()    });  }
19  render() {
20    return (
21      <div>
22        <h1>Bonjour, monde !</h1>
23        <h2>Il est {this.state.date.toLocaleTimeString()}.</h2>
24      </div>
25    );
26  }
27}
28
29ReactDOM.render(
30  <Clock />,
31  document.getElementById('root')
32);

1shouldComponentUpdate(nextProps, nextState) {
2  return true;
3}

1componentDidUpdate(prevProps, prevState, snapshot)