[Arnavion]

>To be clear, "private" variables (including "methods", ie. variables bound to functions) can be implemented anywhere using lexical scope; whether you're pretending to have "classes" or not.

Sure, as long as you declare all methods that require access to said private fields also within that same scope.

For example, TypeScript emits class methods (and getters-setters) as properties on the constructor's prototype. The reason for assigning methods to the prototype instead of each new instance is of course efficiency - you don't want to make new closures every time you create an instance. If the private fields were only available within the constructor body, the methods could not access them.