I very much concur that it is better NOT to introduce TS when explaining JS fundamentals. I've seen smart engineers with a C++ background get tripped up on and very confused working with TS, because it's not clear to them what concepts are "language fundamentals" and what concepts are "the TS transpiler".
(Like expecting that just because you declared something as type X, that it guarantees at runtime it will always be type X, but it won't. You may get data from an API that _says_ it returns type X but the contents don't match. That can be valid code that compiles and has weird runtime behavior)
(Like expecting that just because you declared something as type X, that it guarantees at runtime it will always be type X, but it won't. You may get data from an API that _says_ it returns type X but the contents don't match. That can be valid code that compiles and has weird runtime behavior)