cd.js

class OutOfStockError extends Error {
}

class CD {
    constructor(price, stock) {
        this.price = price;
        this.stock = stock;
    }

    buy(payments, creditCard) {
        if(this.stock == 0){
            throw new OutOfStockError();
        }
        let paymentAccepted = payments.process(this.price, creditCard);
        if(paymentAccepted){
            this.stock--;
        }
    }
}