Angular promise in service

Question

I'm new with Angular promise and I would like to know how to improve my code.

I have a service which preload media or data by calling an API. The media API return an array of urls to preload.

'use strict';
angular.module('myApp').service('PreloaderService', ['$http', '$q', 'localStorageService', function PreloaderService($http, $q, localStorageService) {
 this.preload = function(key){
 var current = 0;
 var deferred = $q.defer();
 switch (key) {
 case 'media':
 // Simplified, in fact it call a config service to get baseUrl
 var url = 'http://myapi/media';
 $http.get(url, {cache: true}).then(function(data) {
 var data = data.data;
 preloadImage(data, localStorageService.get('cachetoken'));
 }, function(data) {
 deferred.reject(data);
 });
 break;
 case 'data':
 var url = 'http://myapi/data';
 $http.get(url, {cache: true}).then(function(data) {
 var data = data.data;
 localStorageService.add('data', data);
 deferred.resolve(data);
 }, function(data) {
 deferred.reject(data);
 });
 break;
 }
 function preloadImage(arrayOfImages, cachetoken) {
 var promises = [];
 var totalImg = arrayOfImages.length;
 for (var i = 0; i < totalImg; i++) {
 (function(url, promise) {
 var img = new Image();
 img.onload = function() {
 var currentStatus = {
 currentImg: ++current,
 totalImg: totalImg
 };
 deferred.notify(currentStatus);
 promise.resolve();
 };
 img.src = url + '&tok=' + cachetoken;
 })(arrayOfImages[i], promises[i] = $.Deferred());
 }
 $.when.apply(,ドル promises).done(function() {
 deferred.resolve('RESOLVED');
 }).fail(function(data) {
 deferred.reject(data);
 });
 }
 return deferred.promise;
 };
}]);

And I call it with

 var promise = Preloader.preload('media');
 promise.then(
 function(){
 $rootScope.preload.imagesLoaded = true;
 },
 function(){},
 function(currentStatus){
 $rootScope.preload.currentImg = currentStatus.currentImg;
 $rootScope.preload.totalImg = currentStatus.totalImg;
 }
 );

• Flambino: I'm really trying hard not to be "that guy", but I can't help myself: "data" and "media" are plural forms already, so "datas" and "medias" isn't quite right. (The singular forms are "datum" and "medium", by the way.)
• konijn: Too late, you're that guy ;)
• Tib: Ahah you are totally right, I updated my question :)

Answer 1

This took a while to parse, it's probably me, I found few flaws with the code, except for a distinct lack of comments.

• I would have made url in preload an optional, 2nd parameter, I would probably want to call preload a few times with different URL's ( for 'data' )

• I think using a switch for media and data is overkill, I would have done a simple if statement.

• Since you have a number of times function(data) {deferred.reject(data);});, I would have assigned this to an actual function.

• {cache: true}, for data seem unfortunately hardcoded, consider this as well as optional parameter ?

• You define current on top, but totalImg in preloadImage, pick one spot and put both vars there

• Sometimes you postfix with Img, sometimes with Images. I would stick everywhere to Images, it is so much more readable

• Except for the angular.module('myApp').service( line, you have succinct lines of code, nice to read

• No need to store a shortcut to data.data in var data = data.data;preloadImage(data, localStorageService.get('cachetoken'));

• I would not have gone down the road of managing an array of promises, I probably would have done a simple if (current===totalImg) deferred.resolve('RESOLVED');

• 'RESOLVED' seems kind of pointless to provide as a parameter to resolve, we know it's resolved ;) Perhaps totalImg + ' images loaded' ?