1npm view react version
2npm view react-script version 

1// To view which version of React is/was used for a particular app, type in the below in commandline/terminal.
2npm view react version
3npm view react-native version

1const REACT_VERSION = React.version;
2
3ReactDOM.render(
4  <div>React version: {REACT_VERSION}</div>,
5  document.getElementById('root')
6);
7<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react.min.js"></script>
8<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react-dom.min.js"></script>
9
10<div id="root"></div>