How does this React code work on CodePen even if no preprocessor is selected?

Question

I have this code on CodePen: https://codepen.io/anon/pen/OdOyJX that works perfectly, and I am confused about why this works.

ReactDOM.render(
  <div>Hello, world!</div>,
  document.getElementById('root')
);

In the JavaScript settings, there is no preprocessor selected, so I expect the JSX syntax to fail as "<" is an invalid token. What makes this work on CodePen?

Answer 1

If you look at your Pen now, it looks like it does indeed fail on the < in your JavaScript, but if you turn Babel on, it works well.

Babel must have been accidentally turned on my default back when you asked this question!