This is the same _type_ of elitism that I've seen from the Scala community and really makes TS seem unpalatable. Big "A monad is just a monoid in the category of endofunctors" vibes.

Yeah, I'm quite sure inverting trees is more relevant to real world programming than knowing the fundamentals of a type system people say they are expert in. /s

In any case, I am against technical interviews and never ask any technical questions beyond just general talk of how people like to work, and their previous projects.

But I know for a fact the overwhelming majority of people that say they know TypeScript don't know a tenth of what's written in the docs, and mapped types were just a very basic example.