<div id="root"></div>

function App() {
  const [message, setMessage] = React.useState('javascript is so cool');

  function handleClick() {
    setMessage('my new message')
  }

  return (
    <div>
      <h1>{message}</h1>
      <button onClick={handleClick}>
        Update the Message!
      </button>
    </div>
  );
}

ReactDOM.render(
  <App />,
  document.getElementById('root')
);