Async calls in loop delayed

Question

I have a function which makes two asynchronous calls to the database inside a loop. The issue is that the return function works before the data from the loop is retrieved.

const myFunc = async (customers) => {
  const customerList = customers.map(async (customer) => {
    const cashCollected = await knex('cash_collections')
      .sum('amount_collected as amount')
      .where('account_code', customer.code)
      .first();
    const orderValue = await knex('orders')
      .sum('discounted_price as amount')
      .where('customer_id', customer.id)
      .first();
    const customerData = {
      name: customer.name,
      outstandingBalance: (orderValue.amount - cashCollected.amount),
    };
    // This line works after console.log(customerList);
    console.log(customerData);
    return customerData;
  });
   // console and return works before data is retrieved 
   // (before console.log(customerData) is run)
  console.log(customerList);
  return customerList;
};

// Function is called in another place
myFunc()

Answer 1

You're making all of those calls in parallel by doing them in the map callback. If you really want to do that, you need to wait for those calls to settle by using Promise.all:

const customerList = await Promise.all(customers.map(async (customer) => {
    // ...
}));

If you want to do them in series instead, use a for loop and await each response. :-) But it looks like parallel is okay.