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AngularJS 1.0.7: Nesting parallel promises with $resources

this post extends a previous one already solved. Please see it, to get in context: Nesting promises with $resources in AngularJS 1.0.7
With that approach in mind, I would like to make a parallel call to functions and when both are completed then run the searchBoats function with the results. I think I can nest the promises, but I also think it can be done in parallel, maybe with $q.all. Unfortunately, this promises topic is confusing for me and I don´t know how to do it.
Taking the previous post example, I would like to do something like:
var parseURL = function() {
var deferred = $q.defer();
var promise = deferred.promise;
promise.then(function success(result) {
console.log(result);
searchBoats(result);
});
// Instead of resolve when parseBoatType promise is returned, I would like to
// wait for two promises
parseBoatType().then(deferred.resolve);
parseDestination().then(deferred.resolve);
// of course, with this code deferred will be resolved when first promise
// comes. Is it possible to use $q.all here?
};
parseURL();

As in your earlier question, there is no need to use a deferred here. Just use $q.all(), which returns a promise:
var parseURL = function() {
$q.all([parseBoatType(), parseDestination()])
.then(function (results) {
console.log(results);
searchBoats(results);
});
};
parseURL();

Resolving promises synchronously with Q.all(promises)

I am using the Kriskowal Q library to handle promises.
I wrote the following function to wait until all promises have been resolved.
function multiplePromises(targetArray) {
var promises = {};
for (var i=0; i<targetArray.length; i++) {
var promise = singlePromise(); // any async. function
promises[i] = promise;
};
return Q.all(promises);
};
and I call it as follows:
multiplePromises(targetArray).then(
function(success){
console.log("success");
},
function(error){
console.log("error", error);
}
);
I was wondering however whether there is an order in which the promises are resolved (e.g. is it synchronous?). I.e. does the function wait to trigger the next promise i+1 until promise i is resolved? Or alternatively is it like with all other async. methods, that it actually fires all the single promises and just waits until they are all done?
If the second is the case, how would one rewrite this function to make sure that promise i+1 is ONLY triggered once promise i has been resolved?
Update: test
I did a test and put:
promises[i] = i;
to check whether it resolves sycnhronously and it seems the case. However, it could be just that my async function is fast enough to actually resolve it that quick. Does this seem right?

there are several ways to achieve what you want
Minimal change to your code would be
function multiplePromises(targetArray) {
var promises = [];
var p = Promise.resolve(); // I don't know the Q equivalent of this
for (var i=0; i<targetArray.length; i++) {
p = p.then(function() {
return singlePromise();
});
promises[i] = p;
};
return Q.all(promises);
};

The promises will be executed by Q in the order you declare them, but there's no way to ensure the return order will be the same. That is how async works.
If you want them to resolve in order, the only way I can think of is calling them one after the other instead of doing it in a batch.
This other response will provide more info and some solutions:
https://stackoverflow.com/a/36795097/7705625

Promises in theory could be resolved in order (and it could be easy to write an example in which they would) but you should never count on that.
The whole point of functions like Promise.all() (or Q.all() or Bluebird.all() etc.) is that if waits for all of the promises to get resolved, no matter what is the order of that, and as soon as they are all resolved then the promise that the Promise.all() itself returns gets resolved with an array of values that the original promises resolved to.
In that array you will get always the same order as the order of promises in the array that was an argument to Promise.all(). But the order in time in which the original promises were resolves is not known and is not relevant, as that will have no effect on the result of using Promise.all() whatsoever.

Wait for 1 promise and then all promises using $q

I'm fairly familiar with how $q works and I use it in angularjs to wait for single promises to resolve and multiple promises to resolve with $q.all().
The question is I'm not sure if its possible to do this (and if it works correctly): Can I wait for a single promise to resolve, but then also run some code when all my promises resolve too... AFTER the success callbacks of the individual promises have finished... for example:
var promises = [];
for(i=1, i<5, i++){
var singlePromise = SomeSevice.getData();
promises.push(singlePromise);
singlePromise.then(function(data){
console.log("This specific promise resolved");
});
}
// note: its important that this runs AFTER the code inside the success
// callback of the single promise runs ....
$q.all(promises).then(function(data){
console.log("ALL PROMISES NOW RESOLVED"); // this code runs when all promises also resolved
});
My question is, does this work as I think it does, or is there some weird async, indeterministic result risk?

A call to then also returns a promise. You can then pass this to your array instead of the original promise. This way your $q.all will run after all your thens have been executed.
var promises = [];
for(i=1, i<5, i++){
// singlePromise - this is now a new promise from the resulting then
var singlePromise = SomeSevice.getData().then(function(data){
console.log("This specific promise resolved");
});
promises.push(singlePromise);
}
$q.all(promises).then(function(data){
console.log("ALL PROMISES NOW RESOLVED");
});

Dynamic array promise sequence

Im getting dynamic (the number of promises can be change each per runtime) array of promises, Now I want that after every resolve or reject
to handle the returned promise before promises array will be finished .
I try with promise all but it's continue after all the promises has done.
if the array (of promises) wasn't be dynamic so I can simply use something like this
but I dont know how much promises I have in the array and I want after every promise fulfilled or ... to proceed with the answer of it and not wait until all the promises will done
firstMethod()
.then(secondMethod)
.then(thirdMethod);
We are using Q ...
Is it possible ?
Update (example )
Lets say I've the promise array
[promise1,promise2,promise3, promiseN]
Now I want that when promise1 finish to process to handle it with then and not wait that all promises will be finished .
The biggest issue here is the array can have N promises and I dont know in RT how much promises I will get until I got this array therefore I cannot use simply then
Update 2 (to clarify a bit more :-) ) The tricky part...
If I Know the size of the array beforehand I can use simply then , 5 entry in the array 5 chain with then but here the tricky part is that I dont know beforehand how much promises I will have in the array of the promises ....

If the goal is to chain each promise with same then but to not wait for all promises to complete, this is just a loop:
for (const promise of promiseArray) {
promise.then(...)
}
If promise results should be joined together in the end, the array can be additionally processed by all:
Promise.all(promiseArray.map(promise => promise.then(...)))
.then(...)
Notice that behaviour for all applies here. If there is uncaught rejection in promise array, only the first rejection will be caught.
This is true for most promise implementations. There may be Q methods that allow do do this easier.

you can use Promise.race()
The Promise.race(iterable) method returns a promise that resolves or rejects as soon as one of the promises in the iterable resolves or rejects, with the value or reason from that promise.
var p1 = new Promise(function(resolve, reject) {
setTimeout(resolve, 500, 'one');
});
var p2 = new Promise(function(resolve, reject) {
setTimeout(resolve, 100, 'two');
});
Promise.race([p1, p2]).then(function(value) {
console.log(value); // "two"
// Both resolve, but p2 is faster
});

If you don't need to chain promises. You could just do:
var tasks = [[promise1, handler1], [promise2, handler2], [promise3, handler3]];
tasks.forEach(function (task) {
var promise = task[0];
var handler = task[1];
promise.then(handler)
});

How to bundle Angular $http.get() calls?

I have a controller that needs to retrieve two separate REST resources that will populate two dropdowns. I would like to avoid populating either of them until both $http.get() calls have returned, so that the dropdowns appear to be populated at the same time, instead of trickling in one after the other.
Is it possible to bundle $http.get() calls and elegantly set the $scope variables for both returned arrays, without having to write state logic for both scenarios, e.g. a returns before b, b returns before a?

The return value of calling the Angular $http function is a Promise object using $q (a promise/deferred implementation inspired by Kris Kowal's Q).
Take a look at the $q.all(promises) method documentation:
Combines multiple promises into a single promise that is resolved when
all of the input promises are resolved.
Parameters
promises – {Array.<Promise>} – An array of promises.
Returns
{Promise} – Returns a single promise that will be resolved with an array of values, each value corresponding to the promise at the same index in the promises array. If any of the promises is resolved with a rejection, this resulting promise will be resolved with the same rejection.
You can use $q.all to "join" the results of your http calls, with code similar to:
app.controller("AppCtrl", function ($scope, $http, $q) {
$q.all([
$http.get('/someUrl1'),
$http.get('/someUrl2')
]).then(function(results) {
/* your logic here */
});
}

do you mean something like this:
function someController( $scope, $http, $q ) {
var first_meth = $http.get("first_url"),
second_meth = $http.get("second_url");
$q.all([first_meth, second_meth]).then(function(all_your_results_array) {
//here you'll get results for both the calls
});
}
Ref: Angular JS Doc

You could use the Async javsscript library here: https://github.com/caolan/async.
Use the series call. It will make the 2 calls and then call one callback when both are done.