Extend String and Storage with some useful properties and methods in my opinion

extend-string-storage.js

/**
 * Set multiple storage items
 * @param {Object} items
 */
Storage.prototype.setItems = function (items) {
    for (let item in items) {
        if (items.hasOwnProperty(item)) {
            let itemToSet = "";
            if (typeof items[item] === 'object')
                itemToSet = JSON.stringify(items[item]);
            else
                itemToSet = items[item];
            
            this.setItem(item, itemToSet)
        }
    }
};

/**
 * Get multiple storage items
 * @returns {Object}
 */
Storage.prototype.getItems = function () {
    let obj = {};
    for (let item in this) {
        if (this.hasOwnProperty(item)) {
            let jsonItem = this.getItemAsJson(item);
            obj[item] = jsonItem.length > 0 ? jsonItem : Object.keys(jsonItem).length > 0 ? jsonItem : this[item];
        }
    }
    return obj;
};

/**
 * Remove multiple storage items
 * @param {Array<String>} items
 */
Storage.prototype.removeItems = function (items) {
    for (let index = 0; index < items.length; index++)
        this.removeItem(items[index]);
};

/**
 * Get item as parsed json
 * @param {String} key
 * @returns {Object|Array}
 */
Storage.prototype.getItemAsJson = function (key) {
    return this[key] ? this[key].isJSON ? JSON.parse(this[key]) : [] : [];
};

Object.defineProperties(String.prototype, {
    isBlank: {
        /**
         * Check if string is blank
         * @return {Boolean}
         */
        get: function () {
            return /^\s*$/.test(this);
        }
    },
    isJSON: {
        /**
         * Check if string is valid json
         * @return {Boolean}
         */
        get: function () {
            let str = this;
            if (str.isBlank) return false;
            str = str.replace(/\\(?:["\\\/bfnrt]|u[0-9a-fA-F]{4})/g, '@');
            str = str.replace(/"[^"\\\n\r]*"|true|false|null|-?\d+(?:\.\d*)?(?:[eE][+\-]?\d+)?/g, ']');
            str = str.replace(/(?:^|:|,)(?:\s*\[)+/g, '');
            return (/^[\],:{}\s]*$/).test(str);
        }
    }
});