class AjaxFormsTestAjaxElementsForm

class AjaxFormsTestAjaxElementsForm extends FormBase {
    
    /**
     * {@inheritdoc}
     */
    public function getFormId() {
        return 'ajax_forms_test_ajax_elements_form';
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildForm(array $form, FormStateInterface $form_state) {
        $callback_object = new Callbacks();
        $form['date'] = [
            '#type' => 'date',
            '#ajax' => [
                'callback' => [
                    $callback_object,
                    'dateCallback',
                ],
            ],
            '#suffix' => '<div id="ajax_date_value">No date yet selected</div>',
        ];
        $form['datetime'] = [
            '#type' => 'datetime',
            '#ajax' => [
                'callback' => [
                    $callback_object,
                    'datetimeCallback',
                ],
                'wrapper' => 'ajax_datetime_value',
            ],
        ];
        $form['datetime_result'] = [
            '#type' => 'markup',
            '#markup' => '<div id="ajax_datetime_value">No datetime selected.</div>',
        ];
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    public function submitForm(array &$form, FormStateInterface $form_state) {
    }

}