const orders = [
  {
    id: 123,
    name: 'Alex',
    age: 32,
    cart: [
      {
        productId: 234,
        price: 23.99,
        quantity: 3,
      },
      {
        productId: 235,
        price: 39.99,
        quantity: 4,
      },
    ],
  },
  {
    id: 124,
    name: 'Steve',
    age: 22,
    cart: [
      {
        productId: 234,
        price: 23.99,
        quantity: 1,
      },
    ],
  },{
    id: 125,
    name: 'Joe',
    age: 43,
  },
];

const findCustomer = customerName => {
  const customer = orders.find(order => order.name === customerName);
  if (!customer) throw new Error('Customer not found');
  return customer;
}

const totalOrderValue = (customerName) => {
  try {
    const customer = findCustomer(customerName);

    if (!customer.cart) {
      return 0;
    }

    const reducer = (sum, {quantity, price}) => sum += quantity * price;
    return customer.cart.reduce(reducer, 0);
  } catch (error) {
    console.log(error.message);
  }
}

console.log(totalOrderValue('Alex')); // 231.93
console.log(totalOrderValue('Steve')); // 23.99
console.log(totalOrderValue('Joe')); // 0
console.log(totalOrderValue('Wally')); // show an error

const invoiceForCustomer = (customerName) => {
  try {
    const customer = findCustomer(customerName);

    if (!customer.cart) {
      return [];
    }

    return customer.cart.map(({quantity, price}) => quantity * price);
  } catch (error) {
    console.log(error.message);
  }
}

console.log(invoiceForCustomer('Alex')); // [ 71.97, 159.96 ]
console.log(invoiceForCustomer('Steve')); // [ 23.99 ]
console.log(invoiceForCustomer('Joe')); // []
console.log(invoiceForCustomer('Wally')); // show an error