Ask HN: Flow in practice (JS type checking)

Has someone experience with introducing flow[1] in a large codebase? I’m primarily interested in practical aspects:

- does the extra overhead really pay off in terms of code quality?

- did you just annotate your own code or did you go down the entire road with flow-typed[2] and custom module mappers?

- how long did it take everyone to understand the limitations and how flow differs from a proper type system? (Especially more junior devs.)

- would you use it again and if so, is there anything you would do better?

[1] https://flow.org/

[2] https://github.com/flowtype/flow-typed