const $debug = $('.debug');
let renderCount = 0;

const Hello = React.memo((props) => {
  $debug.text(`Renders: ${++renderCount}`);
  return (<p>Hello {props.name}</p>);
});


class App extends React.Component {
  constructor(props) {
    super(props);
    this.state = {ticks: 0};
    this.tick = this.tick.bind(this);
  }
  
  tick() {
    this.setState({ ticks: this.state.ticks + 1 });
  }
  
  render() {
    return (
      <div>
        <Hello name="ynon" />
        <Hello name={this.state.ticks} />
        <button onClick={this.tick}>Tick</button>
      </div>
    )
  }
}

ReactDOM.render(<App />, document.querySelector('main'));