TypeScript annotations can also be put into comments. I like TypeScript's approach (JSDoc) better, actually, because it's how you'd want to annotate them even if you didn't have a typechecker, anyway.
Although I still hit enough annoyances that I'd go straight to `.ts` files for my next project.
Re:What I wish I knew about React
by FeloniousHam on Thursday April 30, 2020 @11:15AM
(#23031731)
We started out with Flow, but moved to Typescript not because it's "cool" (I suspect it's the Flow users who are smoking clove cigarettes in black berets), but because the language improvements and tooling support are a huge productivity boost.
The killer is how flexible it is, it incrementally scales from straight JS to full-on type religion. You only have to use as much as you find useful.
On the other hand Flow is much less cool than TypeScript these days. Plus using it for development under Windows have issues, although FB has started paying attention to them.