Angularjs $q.all


Answer :

In javascript there are no block-level scopes only function-level scopes:

Read this article about javaScript Scoping and Hoisting.

See how I debugged your code:

var deferred = $q.defer(); deferred.count = i;  console.log(deferred.count); // 0,1,2,3,4,5 --< all deferred objects  // some code  .success(function(data){    console.log(deferred.count); // 5,5,5,5,5,5 --< only the last deferred object    deferred.resolve(data); }) 
  • When you write var deferred= $q.defer(); inside a for loop it's hoisted to the top of the function, it means that javascript declares this variable on the function scope outside of the for loop.
  • With each loop, the last deferred is overriding the previous one, there is no block-level scope to save a reference to that object.
  • When asynchronous callbacks (success / error) are invoked, they reference only the last deferred object and only it gets resolved, so $q.all is never resolved because it still waits for other deferred objects.
  • What you need is to create an anonymous function for each item you iterate.
  • Since functions do have scopes, the reference to the deferred objects are preserved in a closure scope even after functions are executed.
  • As #dfsq commented: There is no need to manually construct a new deferred object since $http itself returns a promise.

Solution with angular.forEach:

Here is a demo plunker: http://plnkr.co/edit/NGMp4ycmaCqVOmgohN53?p=preview

UploadService.uploadQuestion = function(questions){      var promises = [];      angular.forEach(questions , function(question) {          var promise = $http({             url   : 'upload/question',             method: 'POST',             data  : question         });          promises.push(promise);      });      return $q.all(promises); } 

My favorite way is to use Array#map:

Here is a demo plunker: http://plnkr.co/edit/KYeTWUyxJR4mlU77svw9?p=preview

UploadService.uploadQuestion = function(questions){      var promises = questions.map(function(question) {          return $http({             url   : 'upload/question',             method: 'POST',             data  : question         });      });      return $q.all(promises); } 

$http is a promise too, you can make it simpler:

return $q.all(tasks.map(function(d){         return $http.post('upload/tasks',d).then(someProcessCallback, onErrorCallback);     })); 

The issue seems to be that you are adding the deffered.promise when deffered is itself the promise you should be adding:

Try changing to promises.push(deffered); so you don't add the unwrapped promise to the array.

 UploadService.uploadQuestion = function(questions){              var promises = [];              for(var i = 0 ; i < questions.length ; i++){                  var deffered  = $q.defer();                 var question  = questions[i];                   $http({                      url   : 'upload/question',                     method: 'POST',                     data  : question                 }).                 success(function(data){                     deffered.resolve(data);                 }).                 error(function(error){                     deffered.reject();                 });                  promises.push(deffered);             }              return $q.all(promises);         } 

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