React: Anatomia de um componente

state.jsx

class Counter extends React.Component {
  constructor(props) {
    super(props);
    this.state = {count: 0};
  }
  
  incrementCount() {
    this.setState({
      count: this.state.count + 1
    });
  }
  
  render() {
    return  (
      <div>
        counter: {this.state.count}
        <button type="button" onClick={this.incrementCount.bind(this)}>Increment</button>
      </div>
    );
  }
};

ReactDOM.render(
  <Counter />,
  document.body
);