Helper object to preload images.

ImageHelper.js

define([
    'jquery',
    'underscore'
], function ($, _) {
    
    var ImageHelper = {
        initialize: function () {
            var example = [
                "img/image1.jpg",
                "img/image2.jpg"
            ];

            this.preloader(example, function() {
                // images have been loaded
            });
        },
        
        /**
         * data: an array of images
         * callback: function to execute after
         *           all images have been loaded
         */
        preloader: function(data, callback) {
            var promises = [];
            
            for (var i = 0; i < data.length; i++) {
                (function(url, promise) {
                    var img = new Image();
                    $(img).one('load', function() {
                        promise.resolve();
                    };
                    img.src = url;
                })(data[i], promises[i] = $.Deferred());
            }

            $.when.apply($, promises).done(function() {
                callback();
            });
        }
    };

    return ImageHelper;

});