React Router v4 - peter-mouland/react-lego-2017 GitHub Wiki
https://github.com/peter-mouland/react-lego/compare/react-router-4
react-router v4 is an interesting improvement over v2 (looks like v3 was never released) in that it no longer has a traditional API. The only way to intereact with it is via JSX components and props.
This essentially means, where previously you might have tested the router using :
import { createMemoryHistory } from 'react-router';
const history = createMemoryHistory();
history.push('/')
you must now do something that is more inline with the JSX world that you will be using it in :
import { MemoryRouter } from 'react-router';
mount(<MemoryRouter location="/"/>)
This change in the way of using react-router has had some benefits in that the real-world apps i've been using it have had the code-base reduced, and I think, simiplified.
checkout the comparison between react-router v2 and v4