Get object array promise, then iterate over objects

Question

I am trying to create an array called pw_array, assign the contents of pw_subscribers to that array, then append each object in the pw_array with new key value pairs from the second promise. I am new to promises and having a lot of trouble making this work. Right now when I console.log(pw_customer) inside the second promise, inside the getCustomers function, it is returning what I want. But when I console.log(pw_array) later it is the original array.

var pw_array = [];
//first promise is working correctly
var getPaywhirlSubscribers = new Promise(function(resolve, reject) {

paywhirl.Subscriptions.getsubscribers({limit:100}, function(error, pw_subscribers) {
        Promise.all(JSON.parse(pw_subscribers).forEach(function(pw_subscriber) {
             pw_array.push(pw_subscriber);
        }))
        // console.log(pw_array);
        return resolve(pw_array);
    });
});

var getGatewayReferences = function(pw_array) {
    return new Promise(function(resolve, reject) {
        Promise.all(pw_array.forEach(function(pw_customer) {
            paywhirl.Customers.getCustomer(pw_customer.customer_id, function(error, customer) {
                pw_customer.phone = customer.phone;
                pw_customer.address = customer.address;
                pw_customer.gateway_reference = customer.gateway_reference;
                // this console.log is returning what I want
                // console.log(pw_customer);
            }); 
        }));
        resolve(pw_array);
        // console.log(pw_array);
    });
};

and the promise chain...

getPaywhirlSubscribers.then(getGatewayReferences).then(function(pw_array) {
  // this console.log is returning the original pw_array with pw_subscribers but not with the appended pw_customer keys
  console.log(pw_array);
});

Have you tried to use pw_array.map instead of pw_array.forEach, and for the map return the paywhirl.Customers.getCustomer(... (which I assume makes a promise). This way the next .then will have all the customers. — asosnovsky
– asosnovsky, Commented Nov 28, 2017 at 14:30
@asosnovsky is correct you are only mutating each item in the pw_array given to you by the forEach. Those items are not "connected live" to the original pw_array at that time. You should use .map — gotomanners
– gotomanners, Commented Nov 28, 2017 at 14:38

Jared Smith · Accepted Answer · 2017-11-28 14:46:43Z

2

All of your code can be reduced to

var getPaywhirlSubscribers = function() {
  return new Promise(function(res, rej) {
    paywhirl.Subscriptions.getSubscribers({limit:100}, function(err, subs) {
      if (err) {
        rej(err);
      } else {
        res(JSON.parse(subs));
      }
    });
  });
};

var gatewayRefs = function(promiseOfArray) {
  return promiseOfArray.then(function(subs) {
    return Promise.all(subs.map(function(sub) {
      return new Promise(function(res, rej) {
        paywhirl.Customers.getCustomer(sub.customer_id, function(err, customer) {
          if (err) {
            rej(err);
          } else {
            res(Object.assign({}, sub, customer);
          }
        });
      });
    });
  });
};

gatewayRefs(getPaywhirlSubscribers()).then(function(arrayOfCustomers) {
  // do something with the customer array
});

Note that you can make this even shorter/simpler if you use one of the many utilities available to automatically convert node.js-style error -first callback APIs into Promise-based ones. Search for 'promise denodeify'.

You could also conceivably pull some of the steps out into a .then chain to reduce nesting, but that's as much aesthetic as practical IMHO.

edited Nov 28, 2017 at 14:46

answered Nov 28, 2017 at 14:41

Jared Smith

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1 Comment

Jared Smith Over a year ago

@David no problem. Just remember that you can't 'unbox' a Promise (like putting the values in an external array). You have to deal with the data only in a .then handler. Just keep chaining.

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