localstorage-03.js

/**
 * Fetches the value associated with key from localStorage.  If the key/value aren't in localStorage, you can optional provide a callback to run as a fallback getter.
 * The callback will also be run if the localStorage cache has expired.  You can use {@link LocalStorage#setItem} in the callback to save the results from the callback back to localStorage.
 *
 * @example <caption>Fetch from localStorage with no callback and get the response returned.</caption>
 * var response = LocalStorage.getItem('key');
 *
 * @example <caption>Fetch from localStorage and handle response in a callback.</caption>
 * LocalStorage.getItem('key', function(response) {
 *   if (response === null) {
 *     // Nothing in localStorage.
 *   } else {
 *     // Got data back from localStorage.
 *   }
 * });
 *
 * @kind function
 * @function LocalStorage#getItem
 *
 * @param {!string} key - Name of the key in localStorage.
 * @param {?function} [optionalCallback=null] - If you want to handle the response in a callback, provide a callback and check the response.
 * @returns {*} Returns null if localStorage isn't supported, or the key/value isn't in localStorage, returns anything if it was in localStorage, or returns a callback if key/value was empty in localStorage and callback was provided.
 */
getItem: function (key, optionalCallback) {
    if (!this.supportsLocalStorage()) {
        return null;
    }

    var callback = function (data) {
        data = typeof data !== 'undefined' ? data : null;

        return typeof optionalCallback === 'function' ? optionalCallback(data) : data;
    };

    var value = localStorage.getItem(key);

    if (value !== null) {
        value = JSON.parse(value);

        if (value.hasOwnProperty('__expiry')) {
            var expiry = value.__expiry;
            var now = Date.now();

            if (now >= expiry) {
                this.removeItem(key);

                return callback();
            } else {
                // Return the data object only.
                return callback(value.__data);
            }
        } else {
            // Value doesn't have expiry data, just send it wholesale.
            return callback(value);
        }
    } else {
        return callback();
    }
}