How to inference class type that implements an interface

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Given an interface:

interface IAnInterface {

}

How to reference and point to a class type that implements that interface?

Meaning, given a class:

class AClassThatImplmentsAnInterface implements IAnInterface {

}

How to reference the type that is a class type? If it was just classes we could use typeof:

typeof AClassThatImplementsAnInterface

but at the interface level, which point to all the classes that implements the interface:

typeof IAnInterface

gives the error:

'IAnInterface' only refers to a type, but is being used as a value here. (2693)

I want to do something like:

type IClassTypeMapping = {
 [names in SomeLiteralStringUnion]: Class<IAnInterface>
}

Of course Class doesn't exist in TypeScript. How to reference the equivalent of Class<IAnInterface>? Is it even possible in TypeScript?

typescript
2 Answers

I'm assuming that you are trying to map to the class itself, not to an instance of the class. So basically something with is constructable. I think this type should work for you:

type Class<I, Args extends any[] = any[]> = new(...args: Args) => I;

We are declaring that Class<IAnInterface> can be called with the new keyword and some arguments, and will return an IAnInterface object (the class instance).

The second argument Args allows you to define what the constructor arguments are. If there are no arguments it would be an empty array.

declare const MyClass: Class<IAnInterface, []>;

const instance: IAnInterface = new MyClass();

declare const OtherClass: Class<IAnInterface, [number, string]>;

const otherInstance: IAnInterface = new OtherClass(0, "");

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