how to know which version of react code example

Example: find react version

const REACT_VERSION = React.version;

ReactDOM.render(
  <div>React version: {REACT_VERSION}</div>,
  document.getElementById('root')
);
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react-dom.min.js"></script>

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