state.jsx

//Class
class CounterButton extends Component {
    constructor() {
        super();
        this.state = {
            count: 0
        }
    }
    render() {
        return <button onClick={() => this.setState({ count: this.state.count + 1 })}>
            { this.state.count }
         </button>
    }
}

//Hooks
const CounterButton = props => {
    const [count, setCount] = useState(0);

    return <button onClick={() => setCount(count + 1)}>
            { count }
    </button>
}