code: public function autoComplete($data)
      {
          static $counter = 0;
          $this->inputOptions['class'] .= ' typeahead typeahead-' . (++$counter);
          foreach ($data as &$item) {
              $item = ['word' => $item];
          }
          $this->form->getView()->registerJs("yii.gii.autocomplete($counter, " . Json::htmlEncode($data) . ");");
  
          return $this;
      }
docs: Makes field auto completable
  @param array $data auto complete data (array of callables or scalars)
  @return $this the field object itself