Checking asynchronous values with a loop of $http calls

Question

On my page I have a form of inputs that take in URLs

<div ng-repeat="parent in parents">
   <input ng-model="parent.url" type="text" /> 
</div>
<button ng-click="addParent()"> Add new link </button>

Later I have a button with ng-click that calls a function in my controller, which checks (asynchronously) if the pages with those URLs exist, along with some other (synchronous) checks.

Somehow I need to wait for results to process, collect them and then display some content depending on those results. I tried looping over all $http calls for each URL:

var results = [];
for (let i = 0; i < parents.length; i++) {
  let p = parents[i];
  $http.get(p.url).
  then((res) => { // pages exists
    results.push(true);
  }, (err) => { // page doesn't exist
    results.push(false);
  });
}

But this would return an empty list, since $http calls are asynchronous. Then I can't really check all of my results like this:

if(sync_values){ // this is fine
  if(async_values){ // this is never filled in
    // do something
  }
}

How can I check my results after all $http calls?

---

UPDATE:

I have tried to implement a factory with $q.all() that would collect promises and resolve them. The tricky bit was to resolve values and not promises; I needed to know which pages existed and which were missing. So I managed to come up with the following code for my factory:

let deferred = $q.defer();
let promises = []; 
angular.forEach(parents, function(parent) { 
  promises.push( $http.get(parent.url).then((res) => {
    return true;
  }, (err) => {
    return false;
  }) );
});

$q.all(promises).
then((res) => {
  deferred.resolve(res);
});
return deferred.promise;

Now I return a list of booleans (and I know which pages exist and which don't).

Answer 1

You should use $q:

angular.module('app', [])
.controller('ctrl', ['$q', '$scope', '$http', function($q, $scope, $http){

  $scope.handler = function(){              
     $scope.results = [];
     $scope.loaded = false;
     $scope.parents = [1,2,3,4,5,6,7,8,9,10];
     var promises = [];

     for (var parent in $scope.parents) {        
       let deffered = $q.defer();	  	 
       promises.push(deffered.promise);
       $http.get('https://stackoverflow.com').
         then(res => {  
           console.log('true');
           $scope.results.push(true);
           deffered.resolve(true);
         }, err => {          
           console.log('false');
           $scope.results.push(false);
           deffered.resolve(false);
         });
      }

      $q.all(promises).then(() => {
         console.log('completed');			
         $scope.loaded = true;
      });	  
    }
}])

<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.23/angular.min.js"></script>

<div ng-app='app' ng-controller='ctrl'>
  <input type='button' value='Click' ng-click='handler()'/>
  <div ng-if='loaded'>
    <span ng-repeat='result in results track by $index'>{{result}} </span>
  </div>    
</div>