如何创建购物车(字典函数)以在javascript中添加和删除项

var shoppingCart = {};

function addToCart(itemName, quantity) {
  if (shoppingCart.hasOwnProperty(itemName)) {
    shoppingCart[itemName] += quantity;
  } else {
    shoppingCart[itemName] = quantity;
  }
}

function removeFromCart(itemName) {
  if (shoppingCart.hasOwnProperty(itemName)) {
    delete shoppingCart[itemName];
  }
}

function getCartItems() {
  for (var item in shoppingCart) {
    console.log(item + ": " + shoppingCart[item]);
  }
}