A lot of people will have a bundle that they've transpiled, but use the global React object from pulling in React and ReactDOM from a CDN. Other folks will use a library that offers syntax like:

  elem.div(elem(Component, {prop: 'value'}), {className: 'foo'})

It's surprisingly common, and it's listed not too far down on the React installation page:

https://facebook.github.io/react/docs/installation.html