The ReactCSSTransitionGroup example says it's for when "You want to use ReactCSSTransitionGroup in your reagent web application".

The React animation docs say the "add-on" version is deprecated, though:

ReactTransitionGroup and ReactCSSTransitionGroup have been moved to the react-transition-group package that is maintained by the community. Its 1.x branch is completely API-compatible with the existing addons.

Fortunately, the latest version (2.4.0) of react-transition-group is in cljsjs, so it looks like it should be straightforward to update.

Instead of:

[reagent "0.5.1" :exclusions [cljsjs/react]]
[cljsjs/react-with-addons "0.13.3-0"]

it'd be:

[reagent "0.5.1"]
[cljsjs/react-transition-group "2.4.0-0"]

and the adapt-react-class call would need to be something like:

(def css-transition-group
  (reagent/adapt-react-class react-transition-group/CSSTransition))

Also, .foo-leave would need to be updated to .foo-exit.

I'm still missing something, though, because the compiled JS is giving me a ReferenceError. Help welcome!