<?php
    /** * @file * Contains Drupalajax_exampleAjaxExampleForm */

    namespace Drupalajax_exampleForm;

    use Drupalajax_exampleAjaxAjaxExampleCommand; use DrupalCoreAjaxAjaxResponse;
    use DrupalCoreAjaxCommandInterface;
    use DrupalCoreAjaxChangedCommand;
    use DrupalCoreAjaxCssCommand;
    use DrupalCoreAjaxHtmlCommand;
    use DrupalCoreAjaxInvokeCommand;
    use DrupalCoreFormFormBase;
    use DrupalCoreFormFormStateInterface;

    class AjaxExampleForm extends FormBase{

    /**
     * @param array $form
     * @param FormStateInterface $form_state
     *
     * @return array
     */
    public function buildForm(array $form, FormStateInterface $form_state) {

        $form['submit'] = array(
            '#type' => 'button',
            '#value' => 'Login',
            '#attached' => array(
              'library' => array(
                'ajax_example/ajaxCustom','core/jquery')),
            '#ajax' => array(
                'callback' => 'Drupalajax_exampleFormAjaxExampleForm::ajaxCallOwn',
                'event' => 'click',
                'progress' => array(
                    'type' => 'throbber',
                    'message' => 'ajaxOwn',
                ),
        ));
    }

public function ajaxCallOwn(array &$form, FormStateInterface $form_state)
  {
    $ajax_response = new AjaxResponse();

    //$ajax_response->addCommand(new HtmlCommand('#edit-user-name2--description', "changedDessrition!!!!"));

    $ajax_response->addCommand(new InvokeCommand(NULL,'changeDescription'));
    return $ajax_response;
  }

<?php

/**
 * @file
 * Contains Drupalajax_exampleAjaxAjaxExampleCommand
 */

namespace Drupalajax_exampleAjax;

use DrupalCoreAjaxCommandInterface;

class AjaxExampleCommand implements CommandInterface{

  /**
   * @var string
   */
  protected $blub;
  // Constructs a SystemBlubCommand object.

  /**
   * Constructs an SlideDownCommand object.
   * @param string $blub
   */

  public function __construct() {
    $this->blub = "changed!!!!";
  }

  public function render() {
    return array(
      'command' => 'changeDescription',
      'method' => NULL,
      'blub' => $this->blub,
    );
  }
}

(function ($, Drupal) {

    /**
     * Command to Slide Down page elements before removing them.
     *
     * @param {Drupal.Ajax} [ajax]
     * @param {object} response
     * @param {string} response.blub
     * @param {number} [status]
     */

    Drupal.AjaxCommands.prototype.changeDescription = function (ajax, response, status) {

        alert("asdfasdgf");
        $("#edit-user-name--description").remove();
        $("#edit-user-name--description").html(response.blub);

    };

})(jQuery, Drupal);

ajax_example:
  version: 1.x
  js:
    js/ajaxCustom.js: {}
  dependencies:
    - core/drupal
    - core/drupal.ajax
    - core/jquery