class Bike {
    constructor(model, price) {
        if(typeof model !== 'string' || typeof price !== 'number'){
            throw new Error("Model must be a string, and number must be a number");
        } else {
            this.model = model;
            this.price = price;

            if(Bike.totalPrice) {
                Bike.totalPrice += price;
            } else {
                Bike.totalPrice = price;
            }

            if(Bike.bikeCount) {
                Bike.bikeCount++;
            } else {
                Bike.bikeCount = 1;
            }
        }
    }

    toString(){
        return "Model: " + this.model + " Price: " + this.price + ".kr";
    };

    static avgPricePerBike(){
        return "The average price per bike is " + (Bike.totalPrice/Bike.bikeCount) + ".kr";
    };

    static totalNumberOfBikes(){
      return "There is " + Bike.bikeCount + " bikes in storage";
    };

};

class ElBike extends Bike {
  constructor(model, price, battery) {
      super(model, price);
      this.batteri = battery;
  }
      toString() {
          return super.toString() + "kr. Battery: " + this.batteri;
      }
};

// Test
try {
    let b = new Bike("M1", 23000);
    let eb = new ElBike("Electrical", 200, "Lithium");
    console.log(b.toString());
    console.log(eb.toString());
    console.log(Bike.totalNumberOfBikes());
    console.log(Bike.avgPricePerBike());
    /*
    let b2 = new Bike(2, 20);
    let eb2 = new ElBike(2, 20, "Lithium");
     */
} catch (e) {
    console.log("Error: " + e.message);
}