appendHolders() {
    this.itemHolders = []; // append our three slide holders -
    // previous, current, and next

    for (let i = 0; i < 3; i++) {
      const el = createElement('pswp__item', 'div', this.pswp.container);
      el.setAttribute('role', 'group');
      el.setAttribute('aria-roledescription', 'slide');
      el.setAttribute('aria-hidden', 'true'); // hide nearby item holders until initial zoom animation finishes (to avoid extra Paints)

      el.style.display = i === 1 ? 'block' : 'none';
      this.itemHolders.push({
        el //index: -1

      });
    }
  }
Create and append array of three items
that hold data about slides in DOM