Error handling with Drupal.ajax()

First I am not very good in JavaScript so maybe I do not know some very basics… I apologize in advance.

I created a form where I want to save every change in single fields directly without the need to submit the form each time. Therefore I created a custom route which returns an AjaxResponse on successfull database savings as well as on any errors on the Drupal side.

But I want to be aware of any errors which may appear on the client side as well. $.ajax() has the function .fail() and .done() where I can do different things in my JavaScript when something went wrong. These methods are missing for Drupal.ajax(). Is there any way to react on errors when using Drupal.ajax()?

I tried

try {
  Drupal.ajax({url: path}).execute();
catch (e) {
  alert( + ": " + e.message);

and built in some errors on my controller but all that happens is that the browsers console lists Ajax errors – no alert is shown to the client.