[danielmason]

I'm not sure I understand what you mean by "the client loses most the advantages of your library being in TypeScript in the first place." Your library still exposes a more clearly-defined API by making types explicit. And saying that the downstream consumer doesn't get the benefit of compile-time type checking if they've chosen not to use type checking is...kind of a truism?

[robert_tweed]

The problem is with the author's assertion that all libraries should be using TypeScript and not, say, Flow, or some other alternative that achieves the same goals, perhaps better.

[MadcapJake]

Does Flow offer type definition files?

[AgentME]

Yes. Also, there isn't a need to maintain a separate definitions file[1] if the library was developed as Flow-typed code. I've made a few small libraries[2] that were written with Flow-typed code, and are built so that the types are automatically enforced if you use the library in a Flow-typed project.

[1] A hand-maintained definitions file: https://github.com/facebook/immutable-js/blob/master/type-de... . Sure, it's nice as documentation, but that is a lot of redundant effort if you already have separate documentation, and types and documentation in the original source code too. [2] https://github.com/AgentME/contain-by-screen is one simple example.