Get type of properties unique to a child class

Question

Is it possible to construct a TypeScript type that extracts the property names that are unique to a specific class, that it did not inherit from its parent class? For instance, this works if I know the parent class (Playground Link):

class Parent {
    hello = 'hello'
}

class Child extends Parent {
    world = 'world'
}

type OwnProps<Base, T extends Base> = Exclude<keyof T, keyof Base>

declare const ownProps: OwnProps<Parent, Child> // "world"

However, I would like a way to accomplish the same type of thing, but without explicitly specifying the base class, something like this:

type OwnProps<T, Base = T extends ???> = Exclude<keyof T, keyof Base>

declare const ownProps: OwnProps<Child> // "world"

Is this possible? Is there some kind of conditional magic I can use in place of ??? that would let me infer types that the Child class extends?

Answer 1

Unfortunately it looks impossible. TypeScript uses structural type system and a type doesn't store any information about class hierarchy, i.e. the Child type it's just { hello: string, world: string }.

You can also look at the other similar question: TypeScript: Get Type of Super Class?