[acemarke]

Flow types are _everywhere_ in the codebase.

To pick a specific example, here's the file that implements the core logic for the new Hooks feature:

https://github.com/facebook/react/blob/6cb26774e27e03c7d5d6e...

As for the TS typings, there's been lots of agitation from people asking them to be officially included and shipped with React. But, again, the React devs themselves aren't TS users (that I know of), and so they don't have the expertise to write and maintain those typings. Better that they be left over in DefinitelyTyped for the community to maintain.

(I'm a Redux maintainer, and I feel exactly the same way about the typings for React-Redux. I don't have any actual TS experience myself yet, and I couldn't do anything useful in regards to the React-Redux typings. Plus, I've got far too much else on my plate to worry about those.)