Andela challanges

mainShopCart.js

class ShoppingCart {
  constructor(){
    this.total = 0;
    this.items = { };
  }
  
  addItem(itemName, quantity, price) {
    let cost = quantity * price;
    this.total = this.total + cost;
    this.items[itemName] = quantity;
  }
  
  removeItem(itemName, quantity, price) {
    let cost = quantity * price;
    this.total = this.total - cost;
    let oldQuantity = this.items[itemName];
    this.items[itemName] = (quantity > oldQuantity) ? 0 : oldQuantity - quantity;
  }
  
  checkout(cashPaid) {
    if (cashPaid < this.total) {
      return "Cash paid not enough";
    } else {
      return cashPaid - this.total;
    }
  }
}

class Shop extends ShoppingCart {
  constructor(){
    super();
    this.quantity = 100;
  }
  
  removeItem(...args) {
    if (args.length === 0) {
      this.quantity = this.quantity - 1;
    } else {
      let [itemName, quantity, price] = args;
      let cost = quantity * price;
      this.total = this.total - cost;
      let oldQuantity = this.items[itemName];
      this.items[itemName] = (quantity > oldQuantity) ? 0 : oldQuantity - quantity;
    }
  }
}