Get generic type used to extend a class

I have a class that takes a generic:

abstract class Base<P extends SomeType = SomeType> {
  // ...
}

And a class that extends it:

class A extends Base<SomeTypeA> {
  // ...
}

Its hard to describe, but basically I’m wondering if its possible with typescript to know "What is the type that class A extended Base with?"

Something like

type PropType = ExtendedGeneric<A> // SomeTypeA

>Solution :

You can use a conditional type to extract the type that was passed to Base

type ExtendedGeneric<T extends Base<any>> = T extends Base<infer P> ? P: never
type PropType = ExtendedGeneric<A> // SomeTypeA

Playground Link

You can read more about conditional types here