app.js

export default class CounterApp extends React.Component {
  constructor(props) {
    super(props);
    this.state = { count: 0 };
  }
  render() {
    return (
      <div className="App">
        <button
          onClick={() => {
          this.setState({ count: this.state.count + 1 });
          }}
        >COUNT ({this.state.count})</button>
      </div>
    );
  }
}