Extending vs. implementing a pure abstract class in TypeScript

Question

Suppose I have a pure abstract class (that is, an abstract class without any implementation):

abstract class A {
    abstract m(): void;
}

Answer 1

The implements keyword treats the A class as an interface, that means C has to implement all the methods defined in A, no matter if they have an implementation or not in A. Also there are no calls to super methods in C.

extends behaves more like what you'd expect from the keyword. You have to implement only the abstract methods, and super calls are available/generated.

I guess that in the case of abstract methods it does not make a difference. But you rarely have a class with only abstract methods, if you do it would be much better to just transform it to an interface.

You can easily see this by looking at the generated code. I made a playground example here.