TypeScript has supported abstract classes since 2015, which provides compiler errors if you try to instantiate that class. TypeScript 4.2 adds support for declaring that the constructor function is abstract. This is mostly used by people who use the mixin pattern ( example:mixins ) The mixin pattern involves having classes dynamically wrapping each other to "mixing in" certain features to the end result. This pattern is represented in TypeScript via a chain of constructor functions of the classes, and by declaring one as abstract you can use abstract classes inside your mixins. All mixins start with a generic constructor to pass the T through, now these can be abstract.

type AbstractConstructor = abstract new (...args: any[]) => T

abstract class Animal {
  abstract walk(): void;
  breath() { }
}

// A mixin which adds a new function (in this case, animate)
function animatableAnimal>(Ctor: T) {
  abstract class StopWalking extends Ctor {
    animate() { }
  }
  return StopWalking;
}

class Dog extends animatableAnimal(Animal) {
  walk() { }
}


const dog = new Dog()
dog.breath()
dog.walk()
dog.animate()