Inheriting class method augment types in Typescript

example.ts

abstract class Greeter {
  abstract greet(who: string, message: string): void;
}

class ClassyGreeter extends Greeter {
  greet(who, message) {
    console.log(`Salutations, ${who}. ${message}`);
  }
}

const classyGreeterInstance = new ClassyGreeter();
classyGreeterInstance.greet("Mr Bingley", "Is it not a fine day?"); // OK, inputs are strings
classyGreeterInstance.greet(1234, false); // Should Throw maybe

I think you're expecting a feature of abstract classes that does not exist . From my understanding abstract classes can only insure methods are implemented to desired spec, however the child must insure new instances are follow the desired implementation of the parent. I'm sure they will come up with several use cases for why its done this way but I think you may need open an issue with them you may have the next great feature on your hands.

By default 'any' types are applied to your inputs which are compatible with 'string' types.

However you would throw a ts error if you tried
greet(who:number, message:boolean) {. . .}

which I'm sure you have experienced