Is it possible to setup a project which has code for both React Native(Mobile app) + React(web), having the code shred between platforms except for the UI part.
Have
Yes, absolutely possible. We've done it before using this lib react-native-web. https://github.com/necolas/react-native-web
beside index.ios.js and index.android.js, you will need create index.web.js, the content should be similar like this.
import { AppRegistry } from 'react-native';
import App from './app/Containers/App/App.container';
AppRegistry.registerComponent('ReactNativeWeb', () => App);
AppRegistry.runApplication('ReactNativeWeb', { rootTag: document.getElementById('react-app') });
also you need to create your own nodejs code to serve up the bundle. full reference