class Zoo {
  public static getZooInstance(): Zoo {
    if (!Zoo.zooInstance) {
      this.zooInstance = new Zoo();
    }

    return Zoo.zooInstance;
  }

  private static zooInstance;

  private _animals = [];

  private constructor() { }

  public get animals() {
    return this._animals.join(' - ');
  }

  public addAnimal(animal: string) {
    this._animals.push(animal);
  }
}

const zoo1 = Zoo.getZooInstance();
zoo1.addAnimal('Ivan');
zoo1.addAnimal('Petko');
zoo1.addAnimal('Haralampi');
zoo1.addAnimal('Cenka');
zoo1.addAnimal('Minka');

console.log(zoo1.animals);