Finding the class type that implements an interface: A guide

Consider this scenario:

interface IAnInterface {

}

How can you refer to and point to a class type that implements the interface?

For instance, if we have a class like this:

class AClassThatImplmentsAnInterface implements IAnInterface {

}

What is the method for referencing the type that represents a class? When dealing with just classes, we could use typeof:

typeof AClassThatImplementsAnInterface

However, when it comes to interfaces, which reference all classes implementing that interface, using typeof IAnInterface results in an error:

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

Is there a way to achieve something similar to this:

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

The concept of Class does not exist in TypeScript. How can you reference the equivalent of Class<IAnInterface>? And is it feasible in TypeScript?

Answer №1

If you're looking to map to the class itself and not an instance of the class, you'll need something that is constructible. This type should be suitable for your needs:

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

This code defines a

ConstructableClass<IAnInterface>
that can be initialized with the new keyword along with some arguments, returning an object of type IAnInterface (an instance of the class).

The optional second argument, Args, allows you to specify the constructor's arguments. If no arguments are needed, it defaults to an empty array.

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

const instance: IAnInterface = new MyClass();
declare const OtherClass: ConstructableClass<IAnInterface, [number, string]>;

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

For a hands-on example, check out this Playground Link.

Answer №2

(Solely for Angular Users)

Angular boasts a pre-installed feature called: Type.

Further insights can be found in this relevant thread.

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