Clock (State and Lifecycle)

clock-state-and-lifecycle.markdown

Clock (State and Lifecycle)

A Pen by Matthew Henderson on CodePen.

License.

index.html

<div id="root">
    <!-- This element's contents will be replaced with your component. -->
</div>

script.babel

class Clock 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>
        <h2>'tis: {this.state.date.toLocaleTimeString()}</h2>
      </div>
    );
  }
}

ReactDOM.render(
  <Clock />,
  document.getElementById('root')
);

scripts

<script src="https://unpkg.com/react/umd/react.development.js"></script>
<script src="https://unpkg.com/react-dom/umd/react-dom.development.js"></script>