> I've seen the transition from a Javascript codebase to a Typescript codebase with all strict checks in place to have a similar step change in dev velocity.
The important factor here is "with all strict checks in place". Whenever I hear fellow FE devs complain about how they dislike Typescript, the complaints often seem to center around how it doesn't really offer that many guarantees... only to find out that their typechecker is set to the least strict settings!
I'm not gonna lie, though: the transition from JS to TS absolutely comes with growing pains. This obviously includes actually updating the codebase and adding types, as well as the developer onboarding/learning process. Personally speaking, I found it very jarring to go from a permissive, lightning-fast JS dev cycle to a more methodical Typescript one.
And don't get me started on how frustrating it can be to diagnose weird type errors related to generic types :D