They are good willed but TypeScript doesn't have an official spec, it's an implementation-defined language. It's not C, it's not JavaScript, it's whatever each release wants it to be. This makes it very difficult to follow every version and evolution, you're consistently chasing whatever has been merged on release.
Also on "it's whatever each release wants it to be" - that is hell on earth if you're looking to target consistent software processes and it only gets worse the more you scale (both solution and team).
I get the value of Typescript - hell I've used it extensively myself... it's just that I can't stop feeling like this is all an anti-pattern: trying to make a loosely-typed language a typed language (if you can call it that?). =/