class TermName

class TermName extends EntityField {
    
    /**
     * {@inheritdoc}
     */
    public function getItems(ResultRow $values) {
        $items = parent::getItems($values);
        if ($this->options['convert_spaces']) {
            foreach ($items as &$item) {
                // Replace spaces with hyphens.
                $name = str_replace(' ', '-', $item['raw']->get('value')
                    ->getValue());
                empty($this->options['settings']['link_to_entity']) ? $item['rendered']['#context']['value'] = $name : ($item['rendered']['#title']['#context']['value'] = $name);
            }
        }
        return $items;
    }
    
    /**
     * {@inheritdoc}
     */
    protected function defineOptions() {
        $options = parent::defineOptions();
        $options['convert_spaces'] = [
            'default' => FALSE,
        ];
        return $options;
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildOptionsForm(&$form, FormStateInterface $form_state) {
        $form['convert_spaces'] = [
            '#title' => $this->t('Convert spaces in term names to hyphens'),
            '#type' => 'checkbox',
            '#default_value' => !empty($this->options['convert_spaces']),
        ];
        parent::buildOptionsForm($form, $form_state);
    }

}