Node.js Promises: Push to array asynchronously & save - arrays

Question

I am currently trying to push to an array (attribute within a Mongo Model), from a list of items I receive through a request. From those items, I loop through them to see which one is currently in the db and if that is not the case, then I create a new Item and try to save it. I am using promises to accomplish this task but I am unable to figure out why the array is empty after all the promises have fulfilled.
var q = require('q');
var items_to_get = ['1', '2', '3']; // example array
var trans = new Transaction({
items : []
});
var promises = [];
for (var i = 0; i < items_to_get.length; i++) {
var ith = i; //save current i, kinda hacky
var deferred = q.defer(); //init promise
//find an existing item
Item.findOne({simcode: items_to_get[ith]}, function(err, item) {
trans.items.push(item); // push item to transaction
deferred.resolve(item); // resolve the promise
});
promises.push(deferred); // add promise to array, can be rejected or fulfilled
};
q.allSettled(promises).then(function(result) {
console.log(trans.items); //is empty
trans.save();
}
EDIT Resolved: Code bellow, based on http://jsbin.com/bufecilame/1/edit?html,js,output .. credits go to #macqm
var items_to_get = ['1', '2', '3'];
var promises = []; //I made this global
items_to_get.forEach(item) {
upsertItem(item);
}
q.allSettled(promises).then(function(result) {
//loop through array of promises, add items
result.forEach(function(res) {
if (res.state === "fulfilled") {
trans.items.push(res.value);
}
});
trans.save();
promises = []; //empty array, since it's global.
}
//moved main code inside here
function upsertItem(item) {
var deferred = q.defer(); //init promise
//find an existing item
Item.findOne({simcode: item}, function(err, item) {
deferred.resolve(item); // resolve the promise
// don't forget to handle error cases
// use deffered.reject(item) for those
});
promises.push(deferred); // add promise to array
}

Answer 1

This is how I did it without any 3rd party libraries.
Since I just needed to defer and I'm on ES2017 I figured it was best not to over complicate things with unnecessary dependencies.
'use strict';
/**
* #param {function(*)} callee
* #param {Array} args
* #returns {Promise.<*>}
*/
const defer = (callee, args) => {
return new Promise(resolve => {
resolve(callee(...args));
});
};
/**
* #param {Number} one
* #param {Number} two
* #param {Number} timeout
* #returns {Promise.<Number>}
*/
const asyncFunction = (one, two, timeout) => {
return new Promise(resolve => {
setTimeout(resolve, timeout, one + two);
});
};
let promises = [];
promises.push(defer(asyncFunction, [3, 7, 0])); // returns immediately
promises.push(defer(asyncFunction, [10, 20, 100])); // returns after 100ms
promises.push(defer(asyncFunction, [55, 45, 50])); // returns after 50ms
Promise.all(promises).then(results => {
console.log(results);
});
Run the above code and you'll get [ 10, 30, 100 ].

Answer 2

Instead of
promises.push(deferred);
... try ...
promises.push(deferred.promise);
Also, since your promises are resolving to the item that was saved anyway, you can use the result of q.allSettled(...) as your items:
q.allSettled(promises).then(function(results) {
trans.items = results;
trans.save();
});