Is there an event before and after form is submitted via ajax?
When you look in ajax.js you find several prototype functions, that can be used like hooks in drupal:

core/misc/ajax.js:

 /**
   * Modify form values prior to form submission.
   *
   * @param {object} form_values
   * @param {HTMLElement} element
   * @param {object} options
   */
  Drupal.Ajax.prototype.beforeSubmit = function (form_values, element, options) {
    // This function is left empty to make it simple to override for modules
    // that wish to add functionality here.
  };


You can override this prototype-functions in your own js-file:

(function($) {
   var ajaxBeforeSubmitOriginal = Drupal.Ajax.prototype.beforeSubmit;
   Drupal.Ajax.prototype.beforeSubmit = function (form_values, element_settings, options) {

      // your code  

      // call original function since it can be already overridden 
      ajaxBeforeSubmitOriginal.call(this, form_values, element, options);
   }
})(jQuery);


This is the most basic version. More info: https://www.drupal.org/node/1372840