Get generic type used to extend a class

user_13258781 0
Viewed 77

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
typescript
2 Answers

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

user_1257340

You can add this method in your base:

 abstract getType(): Constructible<Type>;

and you have to define an interface Constructible:

export interface Constructible<T> {
    new (data): T;
}

then in your class A implement the method:

class A extends Base<SomeTypeA> {
  getType(): Constructible<SomeTypeA> {
    return SomeTypeA;
  }
  // ...
}
user_113954660
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