Angular 1.* ; Preloads images in background by using valid css (when in $rootScope 'imgLoading' event emitted and value is false)

angular imagesPreloader directive

//using Lodash (https://lodash.com/)
.directive('imagesPreloader', ['$rootScope', function($rootScope) {
    return {
        restrict: 'A',
        link: function($scope) {
            var willBePreloaded,
                preloadedHashes = {},
                imagesUrls = [];

            var findInPreloaded = function(obj) {
                return preloadedHashes[obj.id] && preloadedHashes[obj.id] === obj.src;
            };

            var isShouldBePreloaded = function(obj) {
                return obj && obj.src && !findInPreloaded(obj);
            };

            $scope.background = '';
            willBePreloaded = function(objects) {
                var values = _.chain(obj)
                    .map(function(snapshot){
                        if (isShouldBePreloaded(obj)) {
                            imagePreload.addPreloaded(obj);
                            return 'url('+obj.src+') no-repeat -9999px -9999px';
                        }
                    })
                    .compact()
                    .value();
                if (!values.length) {
                    return;
                }
                $scope.background = ['background', imagesUrls.join(',')].join(': ') + ';';
            };
            var imagesToPreload = [
                {
                    id:1, 
                    src: 'https://www.google.com.ua/images/branding/googlelogo/1x/googlelogo_white_background_color_272x92dp.png',
                {
                    id:2,
                    src: 'https://www.google.com.ua/images/nav_logo229.png'
                }
            ];
            $rootScope.$watch('imgLoading', function(value) {
                if (_.isUndefined(value) || value) {
                    return;
                }
                willBePreloaded(imagesToPreload);
            });
        }
    }
}])

css

#o-preload-images {
    display: none;
    visibility: hidden;
    position: absolute;
    left: -999em;
}

html

<div images-preloader id="o-preload-images" style="{{'{{background}}'}}"></div>