code: function (index, callback) {
              $.when(pages[index] && pages[index].load())
                  .always(callback);
          }
docs: Call the load method on the page object at the specified index
  @param  {int}      index    The index of the page to load
  @param  {Function} callback Callback function to call always (regardless of page load success/fail)
  @returns {void}