Trigger a Drupal 8+ AJAX Form API submit programmatically

Just some notes on triggering an AJAX Form submit programmatically in Drupal 8+:

• AJAX properties can be found here, but the list was not complete. Especially useful is to know about ''disable-refocus' => TRUE' property, to prevent from refocussing on the submit button after AJAX submit. I added it to the list in the documentation
• Default event for submit, button and image_button is "mousedown" (not "click")! So I also added that information to the API Docs. This is important to know, as triggering a "click" event just won't work! I'm wondering why "mousedown" was chosen and not "mouseup", but that's a different topic.

So here's the snippet I used in Homebox 3.0.x development to implement auto-submit for the AJAX portlet forms:

  /**
   * Implements autosubmit on value change for the portlet forms
   *
   * @type {Drupal~behavior}
   *
   * @prop {Drupal~behaviorAttach} attach
   *   Attach homebox drag drop behaviors.
   */
  behaviors.homeboxPortletAutoSubmit = {
    attach(context) {
      once("porletautosubmit", "input, select, textarea", context).forEach(
        (input) => {
          input.addEventListener(
            "change",
            Drupal.debounce(function () {
              const form = this.closest("form");
              const submitButton = form.querySelector('input[type="submit"]');
              if (submitButton) {
                // Drupal AJAX form submits are triggered on mousedown!
                // @ee https://www.drupal.org/project/drupal/issues/634616
                // @see https://www.drupal.org/files/issues/interdiff-634616-94-99.txt
                // @todo replace jquery code with vanilla code:
                $(submitButton).trigger("mousedown");
              } else {
                form.submit();
              }
            }, 500),
          );
        },
      );
    },
  };