BindInConstructor.js

export default class CounterApp extends React.Component {
  constructor(props) {
    super(props);
    this.state = { count: 0 };
    this.increaseCount = this.increaseCount.bind(this);
  }

  increaseCount() {
    this.setState({ count: this.state.count + 1 });
  }

  render() {
    return (
      <div className="App">
        <button onClick={this.increaseCount}>COUNT ({this.state.count})</button>
      </div>
    );
 }
}