Flow and its unsoundness is horrible. Quite often I can get runtime errors for code that compiled without warnings, and nothing for code that is showing warning

Flow and its unsoundness is horrible. Quite often I can get runtime errors for code that compiled without warnings, and nothing for code that is showing warnings, because, amongst others, Flow's union type resolution is pretty abysmal. Coming from Haskell, the level of unsoundness in Flow is very grating, and I would honestly not recommend it over untyped JavaScript... It luls you into a false sense of confidence that the program is correct, without it actually being so. TypeScript is a lot better in that area.