[React] Click to increase button label

class Button extends React.Component {
	//prevState to avoid race condition
	state = {counter : 0};
	changeLabel = () => {
  	this.setState((prevState) => {
    	return {
      	counter: prevState.counter + 1
      }
    })
  }
	render() {
  	return(
    	<button onClick={this.changeLabel}>
      	{this.state.counter}
      </button>
    )
  }
}

ReactDOM.render(<Button />, mountNode)