class Animal {
  #sound;

  constructor(name, sound) {
    this.name = name;
    this.#sound = sound;
  }

  speak() {
    return `${this.name} says ${this.#sound}`;
  }

  static create(name, sound) {
    return new this(name, sound);
  }
}

class Dog extends Animal {
  #tricks = [];

  constructor(name) {
    super(name, "woof");
  }

  learn(trick) {
    this.#tricks.push(trick);
    return this;
  }

  perform() {
    return `${this.name} performs: ${this.#tricks.join(", ")}`;
  }
}

const rex = Dog.create("Rex", "bark");
rex.learn("sit").learn("shake").learn("roll over");

console.log(rex.speak());
console.log(rex.perform());
console.log(rex instanceof Animal);
console.log(rex instanceof Dog);