Usage with React Router

People often want to animate route transitions, which can result in delightful UX when used in moderation. The first instinct might be to use wrap all routes in TransitionGroup, but that approach requires hacks and falls apart easily when used with trickier components of React Router like Redirect. You should use CSSTransition for each route and manage their in prop on their own.

The main challenge is the exit transition because React Router changes to a new route instantly, so we need to keep the old route around long enough to transition out of it. Fortunately, Route's children prop also accepts a function, which should not be confused with the render prop! Unlike the render prop, children function runs whether the route is matched or not. React Router passes the object containing a match object, which exists if the route matches, otherwise it's null. This enables us to manage the in prop of CSSTransition based on the presence of match.

Exit transitions will cause the content of routes to linger until they disappear, which might pose some styling challenges. Make sure that routes don't affect each other's layout, for example you can remove them from the flow of the document by using absolute or fixed positioning.

Note: When using React Transition Group with React Router, make sure to avoid using the Switch component because it only executes the first matching Route. This would make the exit transition impossible to achieve because the exiting route will no longer match the current URL and the children function won't execute.