ES6 reduce not workd as expected

Question

I have an array of called orders,

const orders = [
  {
    name: 'iPhone 7',
    price: 7199,
    count: 2
  },
  {
    name: 'iPad 2',
    price: 3399,
    count: 1
  },
  {
    name: 'Macbook Pro',
    price: 19888,
    count: 1
  },
  {
    name: 'Kindle Osis',
    price: 2399,
    count: 2
  }
];

and I want to calculate the total price by summing each item's price times count up like this:

orders.reduce((e1, e2) => e1.price * e1.count + e2.price * e2.count);

but I got NaN instead of the total price, anyone can help? Thanks!

Answer 1

You

• forgot to pass 0 as the initial value of a sum
• did not consider that the first argument of the callback is the numeric result from the previous call, not an array element with properties.

So use

orders.reduce((sum, el) => sum + el.price * el.count, 0);