static createCounter(id, ws_) {
    const counter = DOM.createNode('span', id);
    if (ws_.options.showIndex) {
      const link = document.createElement('a');
      link.href = '#';
      link.title = 'View all slides';
      counter.appendChild(link);
    }

    return counter;
  }
Creates the navigation counter.
@param {!String} id Desired ID for the counter.
@param {WebSlides} ws_ WebSlides object.
@return {Element} The arrow element.