Defining additional interfaces

Further extending the class of an extended enum is also possible.

• Define an interface for additional methods or getters.

interface IAnimal {
  readonly favorite: boolean;
  walks(): boolean;
  code(prefix: string): string;
}

• Provide the interface as third type paramter of the extend utility.

enum _Animal { Cat, Dog, Eagle }

class Animal extends extend<typeof _Animal, _Animal, IAnimal>(_Animal) {

}

• Implement the attached interface at the extended class.

class Animal extends extend<typeof _Animal, _Animal, IAnimal>(_Animal) {

  get favorite(): boolean {
    return this.is(Animal.Dog);
  }

  walks(): boolean {
    return this.isNot(Animal.Eagle);
  }

  code(prefix: string): string {
    return `${prefix}:${this.toString()}`;
  }

}

Now, all the enum values will implement the attached interface.

Animal.Dog.favorite; // true
Aniaml.Cat.favorite; // false

Animal.Dog.walks();   // true
Animal.Eagle.walks(); // false

Animal.Cat.code('animal'); // "animal:0"