How to resolve nested promises?

Question

I'm trying to resolve multiple promises scattered across objects inside an array. Here is a simplistic version of my code:

 const getOrderSum = order_id => { return new Promise(resolve => { setTimeout(() => resolve(34), 1000) }) } const customer_array = [ { customer_id: '19847743234730384', name: 'Customer 1', orders: [ { order_id: '98749873244324', price_per: 12 }, { order_id: '9874987323545', price_per: 16 } ] }, { customer_id: '123454351234123', name: 'Customer 2', orders: [ { order_id: '918741433423', price_per: 6 } ] } ] const result_array = customer_array.map(customer => { const promises = customer.orders.map(async order => { order.order_total = await getOrderSum(); return order; }); customer.orders = promises; return customer; }) console.log(result_array);

Inside the map loops I want to make a call to an async function that returns an order_total for each order. result_array looks like this after the code runs:

[
  {
    customer_id: '19847743234730384',
    name: 'Customer 1',
    orders: [ [Promise], [Promise] ]
  },
  {
    customer_id: '123454351234123',
    name: 'Customer 2',
    orders: [ [Promise] ]
  }
]

How do I resolve all of those 3 promises at once and get this:

[
    {
        customer_id: '19847743234730384',
        name: 'Customer 1',
        orders: [
            {
                order_id: '98749873244324',
                price_per: 12,
                order_total: 34
            },
            {
                order_id: '9874987323545',
                price_per: 16,
                order_total: 34
            }
        ]
    },
    {
        customer_id: '123454351234123',
        name: 'Customer 2',
        orders: [
            {
                order_id: '918741433423',
                price_per: 6,
                order_total: 34
            }
        ]
    }
]

Where would I use Promise.all considering that the promises are not in one array?

Answer 1

Please check the code below:

 const getOrderSum = order_id => { return new Promise(resolve => { setTimeout(() => resolve(34), 1000) }) } const customer_array = [{ customer_id: '19847743234730384', name: 'Customer 1', orders: [{ order_id: '98749873244324', price_per: 12 }, { order_id: '9874987323545', price_per: 16 } ] }, { customer_id: '123454351234123', name: 'Customer 2', orders: [{ order_id: '918741433423', price_per: 6 }] } ] let promises = []; const result_array = customer_array.map(customer => { customer.orders.map((order) => { const p = getOrderSum().then((order_total) => { order.order_total = order_total; }); promises.push(p); return order; }); return customer; }); Promise.all(promises).then(() => { console.log(result_array) });

Answer 2

1. Make customer_array.map as async .
2. Use await Promise.all with customer.orders.map so that it will return result instead of Promise .
3. As we have make customer_array.map as async and it is not wrapped inside async function so we need to resolve it with Promise.all().then() .Write your required code inside then .

Try it below.

 const getOrderSum = order_id => { return new Promise(resolve => { setTimeout(() => resolve(34), 1000) }) } const customer_array = [{ customer_id: '19847743234730384', name: 'Customer 1', orders: [{ order_id: '98749873244324', price_per: 12 }, { order_id: '9874987323545', price_per: 16 } ] }, { customer_id: '123454351234123', name: 'Customer 2', orders: [{ order_id: '918741433423', price_per: 6 }] } ] const promises = customer_array.map(async customer => { customer.orders = await Promise.all(customer.orders.map(async order => { order.order_total = await getOrderSum(); return order; })); return customer; }); Promise.all(promises).then(results => console.log(results));

Answer 3

You can use promise.all for that and then use use.then method to resolve the value