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Resolving a promise in Angular Service

We have a service, lets call it AccountService which exposes a method called getAccounts(customerId) among others.
In its implementation all it does is to fire up a $http GET request and return a promise to the calling controller which will put the returned array of accounts in the controller scope once resolved.
On a simplified view all looks like below:
// The service
.factory('AccountService', ['$http', function($http) {
var _getAccounts = function(customerId) {
var request = {
'method': 'GET',
'url': 'http://localhost:8081/accounts/' + customerId
};
return $(request);
};
return {
getAccounts: _getAccounts
};
}]);
// Inside the conntroller
AccountService.getAccounts($scope.customerId)
.then(function(response) {
$scope.accounts = response.data;
});
So once the promise will resolve the controller scope will get populated with the list of accounts.
Note that I kept the above code as simple as I could to get you the idea of what my problem is but in reality it will be code to deal with exceptions, watcher to refresh, etc. Everything works fine.
My problem is that this AccountService is used from lots of controllers and putting the promise resolve in all of these looks to me not only repeating all this boiler plate resolver code but also complicating the unit testing as I am obliged to r/test both successful and exception scenarios in every single controller test.
So my question is:
Is there a nice way to resolve the promise in the service and return the response to the controller, not the promise?
Please note I am a very beginner with Angular and JS so please be gentle if my question looks naive. I have heaps of java experience and my mind seems to go java like everywhere which may not be the case.
Thank you in advance for your inputs

To answer your original question:
Is there a nice way to resolve the promise in the service and return the response to the controller, not the promise?
In my opinion, no, there isn't. It boils down to the way asynchronous calls work - you either pass a callback (and the method returns nothing), or you don't pass a callback and the method returns an object which will be notified (a promise). There may be some workarounds, but I don't think it gets nicer than that.
One way to partially reduce the boilerplate is to use a catch in the service, and return the promise returned by it instead.
Consider the following extremely simplified example:
angular.module('myApp')
.factory('NetworkRequests', [
function() {
var _getData = function() {
var promise = new Promise((resolve, reject) => {
var a = true,
data = ['a', 'b', 'c'];
if (a) {
resolve(data);
} else {
reject('Rejection reason: ...');
}
});
return promise.catch((error) => {
// Notify some error handling service etc.
console.log(error);
return [];
});
};
return {
getData: _getData
};
}
]);
The promise variable would be the result from your http request. You should return some data in the catch function that makes sense in the controller context (e.g. empty array). Then you don't have to bother with error handling in the controller:
angular.module('myApp')
.controller('DataController', ['NetworkRequests',
function(NetworkRequests) {
NetworkRequests.getData().then((data) => {
this.data = data;
});
}
]);
Again, this doesn't solve the complete issue, but at least the error handling part can be encapsulated in the service.

You can design in such a way that once your $http is done with fetching the data, store it your factory variable (somewhat a cache), and for subsequent factory calls, you check if the cache has such data. If yes, return the cache data, else call the $http calls.
Here is the code:
.factory('AccountService', ['$http', '$q', function($http, $q) {
var cachedData = null;
var defered = $q.defer(); //create our own defered object
var _getAccounts = function(customerId) {
if (cachedData !== null) {
console.log('get from cachedData')
defered.resolve(cachedData); // resolve it so that the data is passed outside
return defered.promise; //return your own promise if cached data is found
} else {
var request = {
'method': 'GET',
'url': 'mockdata.json'
};
return $http(request).then((response) => { //return a normal $http promise if it is not.
console.log('get from $http');
cachedData = response.data;
return cachedData;
});
}
};
return {
getAccounts: _getAccounts
};
}]);
Here is the working plnkr. You can open up the console, and click the GetData button. You will see that first time it logs get from $http, where as subsequent calls it logs get from cachedData.

One way is to reuse an object and fill it with data. It is used by ngResource.
It is something like
var data = [];
function getAccounts(customerId) {
var promise = $http(...).then((response) => {
Object.assign(promise.data, response.data)
});
promise.data = [];
return promise;
};
Data is available for binding as $scope.accounts = AccountService.getAccounts(...).data. The obvious drawback is that there is a splash of unloaded content.
Another way is the one you've mentioned. It is being used most frequently. If there is a problem with WET code in controllers, it should be treated by eliminating WET code with class inheritance, not by changing the way it works.
Yet another way is the recommended one. Using a router and route/state resolvers eliminates the need for asynchronously loaded data. The data resolved in resolver is injected into route template as an array.

how to call a factory from a regular function in AngularJs

I have this factory which is called by some controllers.
app.factory('fileData', function($http) {
return {
get: function(filename){ return $http({ method: 'GET', url: filename});
}
};
});
Now I want to call it from a regular function and return the data from the factory. How can I do that? This one does not work because the fileData passed in is not recognized without $scope.
function getData (file, fileData) {
rels = [];
var handleSuccess = function(data, status) {
rels = data;
console.log(rels);
};
fileData.get(filename).success(handleSuccess);
return rels;
}
Any idea how to go around this?

Move return rels inside handleSuccess, you're returning before handleSuccess is getting called. So you're signaling that the function completed execution prematurely.
function getData (file, fileData) {
rels = [];
var handleSuccess = function(data, status) {
rels = data;
console.log(rels);
return rels; // Return rels when the Promise is finished
};
fileData.get(file).success(handleSuccess);
}
Since you're returning the promise from $http, you need to handle its execution in an asynchronous way which, is simply not returning until the promise is resolved.
It would also be a good idea to add a reject handler.
Additionally, .success() is deprecated and you should use .then() and .catch() respectively for handling resolve() and reject() of the Promise appropriately.
See below for the preferred approach to Promises with $http
fileData.get(file)
.then(handleSuccess)
.catch(handleFailure); // Handle any errors returned from $http
EDIT Update for DI example for controller
You need to inject the fileData factory into your Angular Controller. For more info on Dependency Inject see the Angular Docs for DI. Just to note, DI is a huge piece of Angular so it is pretty fundamental to understand this before proceeding.
angular
.module('yourApp')
.controller('yourController', ['$scope', 'fileData', function($scope, fileData) {
// Expose getData via $scope
$scope.getData = getData;
function getData(file, fileData) {
var rels = [];
var handleSuccess = function(data, status) {
rels = data;
console.log(rels);
return rels;
};
fileData.get(file)
.then(handleSuccess);
}
}]);

Your call to the method exposed in the factory (get) uses the $http service which returns a promise. So you cannot get the result of this call in a synchronous way.
In your sample the return rels happens way before the handleSuccess method is called and thus you are returning the old value (an empty array).
The reason it works inside of a controller function is that the controller instance is living for a longer time and when the server call returns successfully, the variable in you controller's $scope is assigned (which then is reflected in your UI via the angular data binding).
So the best way to solve this, is to avoid having a synchronous api in your "regular function". Could you probably make this also async by returning a promise?

AngularJS Service returning data instead of promise

I have a question conserning the use of services or factories inside an AngularJS application.
I Want to write a service that will return data from an Api which i can use inside my controllers.
Lets say i want to have a call like $scope.people = myPeopleService.getPeople();
and inside my service want to check if i already have people and return those otherwise i want to do a $http.get() and fill the people inside my service and then return them. I do not want to have .then inside my controller. Is this even possible?

If you dont want to return the promise to the consumer of your service:
.service('...', function ($http) {
var cachedResponse;
this.getStuff = function () {
if (cachedResponse) {
return cachedResponse;
}
return $http.get('someUrl')
.then(function (response) {
cachedResponse = response;
return response; // Return the response of your $http call.
});
};
});

My solution is to return a reference to an object that might be empty at first, but will hold the data eventually:
app.factory('myPeopleService', function($http){
var people = {};
$http
.post( "/api/PeopleService/getInitData", {
}).success(function (data, status, headers, config) {
angular.extend(people, data);
}).error(function (data, status, headers, config) {
});
return {
getPeople: function () {
return people;
}
};
});
the key is to use angular.extend in order to preserve the object reference.
in the controller you can use ng-show until the data is fulfilled, and/or use watch for processing

You won't be able to escape that at some level, somewhere, this call is asynchronous. One part of your question is easy, caching data is just an option in the $http call:
$http.get(url, {cache: true})
If you expose this call from a service only one call will be made over the network, no changes are required in your controller code.
Another thing to look into is using your router's resolve feature (ui-router and the vanilla router both support resolve). This can clean up some of the code in your controller.

It is not possible to do it without a .then in your use case. Since you want to make use of $http to fetch the people and return them (if they were not present already). $http works asynchronously and would return a promise. Due to the asynchronous behavior of $http it becomes mandatory to handle the promise returned in the calling function.
Hope this helps!

Issue with race condition betwen 2 Controllers in Angular.js with Ajax and a localStorage value

The value for myIdentity is created only once and is persistant saved in the local storage after first usage of the following Angular.js controller.
The function $scope.createIdentity() is a complex function in a more global controller and saves the result to $localstorage.myIdentity.
This perfectly works!!! the createIdentity() function works with Q promise inside for itself.
But in the AppCtrl I have an issue with race conditions because $localstorage.myIdentity is not yet resolved before
my $http XHR Request is fired. So it doesn’t contain any value for myId.
This occurs only the first time the controller is used.
But I need to start the socket.io connection at the first call of the AppCtrl and this is here an bigger problem for me.
At a second usage of AppCtrl the correct value for myIdentity is yet available in $localStorage.
TimeacleControllers.controller('StatusCtrl', ['$scope', '$http', 'Socket', '$localStorage',
function ($scope, $http, Socket, $localStorage) {
if ($localStorage.myIdentity === undefined) {
$scope.createIdentity();
}
var myParams = {
myId: $localStorage.myIdentity
};
$http
.post('http://example.org', myParams)
.success(function (data) {
console.log('received data: ' + data);
Socket.connect();
Socket.on('connected', function () {
console.log("Connection!");
});
Socket.on('message', function (msg) {
console.log("Message: " + msg);
});
})
.error(function (err) {
// Handle login errors here
console.log("Error - " + err);
});
}]);
So what can you do here to make the Ajax Request wait until the $localstorage.myIdentity can be resolved? Please help.

You mentioned about Q promise but having problem with async sequence...?
If createIdentity is returning a promise, just put the http call inside .then
$scope.createIdentity().then(function() {
$http.... // or you can wrap it inside a function
})
Edit: If you have no access to the code that populate the variable (normally happens inside directive), you can setup a one time watch to monitor the value change.
var unwatch = $scope.$watch(function(){
return $localStorage.myIdentity;
}, function(newValue){
if (newValue === undefined) return;
$http...
unwatch();
});

You said $scope.createIdentity() uses a promise (and presumably is an async operation). Make it return a promise for your code to observe. When it resolves, make it resolve the identity.
Promises are chainable. When you return a promise from then, the next then listens for that promise instead of the original promise. In this case, we make the next then listen to the AJAX.
$scope.createIdentity().then(function(identity){
// When createIdentity resolves, use the data for the AJAX.
// Return the AJAX promise for the next chained then.
return $http.get(...);
}).then(function(data){
// When the AJAX completes, use the data for the socket call
Socket.connect();
...
});

Fetch data using $http for use with a custom service

I'm trying to create a custom service which pulls the list of all defined statuses from the server for use in forms, so far I have:
SimpleTaskApp.factory('storyStatus', function($http) {
var data = null;
var promise = $http({
url: '/story-status/',
method: 'GET'
}).success(function (resp) {
data = resp;
});
return {list: data }};
});
I understand this won't work since $http is asynchronous, however I have no desire to run the request more than once. I'd like to treat it as a static variable in effect, so if ever storyStatus.list is called, it should check whether it is empty and then attempt to populate itself.

You should work with promises instead of against them.
You don't need to store the data because you can store the promise. The point of promises is that you don't know when they'll be done. You don't know when your data will be available.
So your service must return the promise. But that's okay:
SimpleTaskApp.factory('storyStatus', function($http) {
var promise;
function getData() {
if ( ! angular.isDefined( promise ) ) {
promise = $http({
url: '/story-status/',
method: 'GET'
});
}
return promise;
}
return { list: getData };
});
In this service, your $http call will only be called once, but will return a promise whenever you call SimpleTaskApp.list(). Your controller that calls it doesn't need to know if the data is there yet because it will react the same regardless, e.g.:
SimpleTaskApp.controller('MainCtrl', function($scope, storyStatus) {
storyStatus.list().then(function( data ) {
$scope.statuses = data.statuses;
});
});
If the data is already retrieved, the then will run basically immediately; if not, it will run when the data gets back. The controller doesn't need to know anything about the internal state of the storyStatus service.
So promises not only help with asynchronous tasks, but they also help keep our components decoupled, which is a big deal in AngularJS - and should be in other frameworks too!

You could do this maybe?
SimpleTaskApp.factory('storyStatus', function($http) {
var promise = $http({
url: '/story-status/',
method: 'GET'
});
return { list: promise };
});
Calling code
storyStatus.list.then(function (data) {
});
You might want to consider using a synchronous ajax call to simplify your API if you are only loading the list once.