React Router v3 provides onEnter, onUpdate, and onLeave methods. These were essentially recreating React's lifecycle methods.

With v4, you should use the lifecycle methods of the component rendered by a <Route>. Instead of onEnter, you would use componentDidMount or componentWillMount. Where you would use onUpdate, you can use componentDidUpdate or componentWillUpdate (or possibly componentWillReceiveProps). onLeave can be replaced with componentWillUnmount.