class AjaxFormsTestValidationForm

class AjaxFormsTestValidationForm extends FormBase {
    
    /**
     * {@inheritdoc}
     */
    public function getFormId() {
        return 'ajax_forms_test_validation_form';
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildForm(array $form, FormStateInterface $form_state) {
        $form['drivertext'] = [
            '#title' => $this->t('AJAX-enabled textfield.'),
            '#description' => $this->t("When this one AJAX-triggers and the spare required field is empty, you should not get an error."),
            '#type' => 'textfield',
            '#default_value' => $form_state->getValue('drivertext', ''),
            '#ajax' => [
                'callback' => 'ajax_forms_test_validation_form_callback',
                'wrapper' => 'message_area',
                'method' => 'replace',
            ],
            '#suffix' => '<div id="message_area"></div>',
        ];
        $form['drivernumber'] = [
            '#title' => $this->t('AJAX-enabled number field.'),
            '#description' => $this->t("When this one AJAX-triggers and the spare required field is empty, you should not get an error."),
            '#type' => 'number',
            '#default_value' => $form_state->getValue('drivernumber', ''),
            '#ajax' => [
                'callback' => 'ajax_forms_test_validation_number_form_callback',
                'wrapper' => 'message_area_number',
                'method' => 'replace',
            ],
            '#suffix' => '<div id="message_area_number"></div>',
        ];
        $form['spare_required_field'] = [
            '#title' => $this->t("Spare Required Field"),
            '#type' => 'textfield',
            '#required' => TRUE,
        ];
        $form['submit'] = [
            '#type' => 'submit',
            '#value' => $this->t('Submit'),
        ];
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    public function submitForm(array &$form, FormStateInterface $form_state) {
        $this->messenger()
            ->addStatus($this->t("Validation form submitted"));
    }

}