Angular 1.* ; Preloads images in background by using js (using lodash https://lodash.com/)

angular imagePreload service

.service('imagePreload', ['$filter', 'createHeadLink', 'hash', function($filter, createHeadLink, hash) {
    var preloadedHashes = {},
        notLoaded = {},
        findInPreloaded = function(obj) {
            return preloadedHashes[hash(obj.id)] && preloadedHashes[hash(obj.id)] === obj.src;
        },
        isShouldBePreloaded = function(obj) {
            return obj && obj.src && !findInPreloaded(obj);
        },
        addPreloaded = function(obj) {
            preloadedHashes[hash(obj.id)] = obj.src;
        };
    return {
        preloaded: preloadedHashes,
        isShouldBePreloaded: isShouldBePreloaded,
        isNotLoaded: function(obj) {
            return notLoaded[obj.id] && notLoaded[obj.id] === obj.src;
        },
        preload: function(objects) {
            _.chain(objects)
                .map(function(obj){
                    if (isShouldBePreloaded(obj)) {
                        return obj;
                    }
                })
                .compact()
                .forEach(function(obj){
                    var img = new Image();
                    img.onerror  = function() {
                        notLoaded[obj.id] = obj.src;
                    };
                    img.src = obj.src;
                    addPreloaded(obj);
                });
        },
        addPreloadLinks: function(obj) {
            if (!isShouldBePreloaded(obj)) {
                return;
            }
            if (page_data['preload']) {
                createHeadLink('preload', obj.src, 'image');
            }
        }
    }
}])

createHeadLink service (used in imagePreload)

.service('createHeadLink', ['$document', function($document) {
    return function(type, href, asType) {
        var params, elemTag = 'link';
        if (_.isObject(type) && _.isUndefined(href)) {
            params = type;
        }
        if (!_.isObject(type) && _.isEmpty(href)) {
            return;
        }
        if (params) {
            elemTag = params.tag;
        }
        var element = document.createElement(elemTag);
        if (params && _.isArray(params.attrs)) {
            _.forEach(params.attrs, function(attr) {
                element.setAttribute(attr.name, attr.value);
            });
        } else {
            if (type === 'preload') {
                element.setAttribute("as", asType);
            }
            element.setAttribute("rel", type);
            element.setAttribute("href", href);
        }
        $document.find("head").append(element);
    }
}])

hash service (used in imagePreload)

.service('hash', ['$filter', function($filter) {
    /**
     * Javascript implementation of Java’s String.hashCode() method
     * @param {String} str
     * @param {Boolean} inHex
     * @returns {String}
     */
    var hashCode = function(str, inHex, radix) {
        if (_.isObject(str)) {
            str = _.toPairs(str);
        }
        if (!_.isString(str)) {
            str = !str ? '0' : str.toString();
        }
        var hash = 0, i = 0,
            length = str.length;
        if (!length) {
            return hash;
        }
        for (; i < length; i++) {
            hash = ((hash << 5) - hash) + str.charCodeAt(i);
            hash = hash & hash;
        }
        radix = inHex ? 16 : (radix ? radix : 10);
        return Math.abs(hash).toString(radix);
    }
    return function(value) {
        return hashCode(value, 0, 36);
    }
}])

how to use

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'
    }
];
imagePreload = $injector.get('imagePreload'); //or any other way to inject
imagePreload.preload(imagesToPreload); //preloading images
imagePreload.isNotLoaded(obj) // can be checked loaded image or not