Big scare quotes there, you can't really 'prove' much in typescript. Don't get me wrong, it's a nice type system they've tacked on to JS, but it's far and away from proofs of correctness. At best, it's an optional type system with escape hatches.
You can only 'prove' what you expect from your design. This works in most cases and saves a lot of guesswork on big, unfamiliar projects. It's not an integral part of JS though, so I wouldn't recommend learning it as a foundation.