react-hello-world

index.html

<div id="timer-example"></div>

react-hello-world.markdown

react-hello-world

A Pen by Matthew Henderson on CodePen.

License.

script.babel

class Timer extends React.Component {
  constructor(props) {
    super(props);
    this.state = { seconds: 0 };
  }

  tick() {
    this.setState(state => ({
      seconds: state.seconds + 1
    }));
  }

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

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

  render() {
    return (
      <div>
        Seconds: {this.state.seconds}
      </div>
    );
  }
}

ReactDOM.render(
  <Timer />,
  document.getElementById('timer-example')
);

scripts

<script src="//unpkg.com/react/umd/react.development.js"></script>
<script src="//unpkg.com/react-dom/umd/react-dom.development.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/16.8.6/umd/react.production.min.js"></script>