class Vehicle {
  #speed = 0;

  constructor(brand) {
    this.brand = brand;
  }

  accelerate(amount) {
    this.#speed += amount;
    return this;
  }

  getSpeed() {
    return this.#speed;
  }

  toString() {
    return `${this.brand} @ ${this.#speed}km/h`;
  }
}

class Car extends Vehicle {
  #gear = 1;

  constructor(brand, model) {
    super(brand);
    this.model = model;
  }

  shiftUp() {
    this.#gear++;
    return this;
  }

  toString() {
    return `${super.toString()} [Gear ${this.#gear}]`;
  }
}

const car = new Car("Toyota", "Supra");
car.accelerate(60).accelerate(40).shiftUp().shiftUp();

console.log(car.toString());
console.log(car instanceof Car);
console.log(car instanceof Vehicle);
console.log(Object.getPrototypeOf(Car) === Vehicle);