hello.html

web-cheat/react/hello.html
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<script src="https://unpkg.com/react@17/umd/react.development.js"></script>
<script src="https://unpkg.com/react-dom@17/umd/react-dom.development.js"></script>
<script src="https://unpkg.com/@babel/standalone@7.14.7/babel.min.js"></script>
</head>
<body>
<p><a href="https://cirosantilli.com/react">https://cirosantilli.com/react</a></p>
<div id="root"></div>
<script type="text/babel">
class Main extends React.Component {
  constructor(props) {
    super(props);
    console.log('Main.constructor');
    this.state = {n: 0};
    this.handleClick = this.handleClick.bind(this);
  }

  handleClick() {
    console.log('Main.handleClick');
    this.setState((state, props) => ({
      n: state.n + 1
    }));
  }

  render() {
    console.log('Main.render');
    return (
      <div>
        <div onClick={this.handleClick}>Click me</div>
        <div>{this.state.n}</div>
        <div>{Math.floor(this.state.n / 2)}</div>
      </div>
    );
  }
}

ReactDOM.render(
  <Main/>,
  document.getElementById('root')
);
</script>
</body>
</html>