React 101

HTML

<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.4.0/react.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.4.0/react-dom.min.js"></script>
<div id="app"/>

Babel + JSX

const App = ({ onClick }) => (
	<div>
	  <button onClick={handleClick}>Click Me</button>
	</div>
);

function handleClick() {
	alert("Button Clicked");
}

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