Hi, I’ve been doing TypeScript in my day-job and hobbies for six and a bit years now. I would not write JS in any other way.
TS is also a superset of JS so all JS is valid (unless you turn on strict
mode). So there is no productivity loss/learning curve unless you want there to be.
In fact, a lot of people who think they’re not using typescript are using it because their editors use typescript definitions for autocomplete and JSDoc type signatures are powered by typescript.
I think they’re lawful evil, more devils than demons.