(I've used Flow for a long time. I'm starting to transition a large codebase from Flow to Typescript, and I'd highly recommend anyone to just start with Typescript rather than Flow. Flow's type inference isn't all that useful, and causes Flow to be magnitudes slower than Typescript. In a large codebase, it can take Flow tens of seconds to minutes to react to a code change and show you errors or auto-completions in your code after typing in an editor, compared to practically instantaneous updates with Typescript.)

TS also doesn't need typedefs for every JS lib. It now defaults to assuming any module import is type `any` if it doesn't have typedefs and can't infer from the JS files for whatever reason.

In the case of the comment above the complication is using JS libs and also the compiler flag --noImplicitAny which causes an error on importing a module that defaults to type `any`. Making that an explicit `any` (with a `declare module "modulename";` in a .d.ts file) is all that is needed.