Some animations need to be run in javascript though, and doing that through state is a bad idea. You can use ref, and sometimes that's fine, but if the data is changing (hitting a moving target), then you need communication. Think coach-marks and scrolling at the same time.
And "tweening" views means showing the last view fade out while the next one fades in (or scrolls in, etc). This means displaying an old state, and a new state at the same time. The trick is to recycle your html elements, but it'll fight you for it.
