constructor(imageSrc, container) {
    // Create placeholder
    // (stretched thumbnail or simple div behind the main image)

    /** @type {HTMLImageElement | HTMLDivElement | null} */
    this.element = createElement('pswp__img pswp__img--placeholder', imageSrc ? 'img' : 'div', container);

    if (imageSrc) {
      const imgEl =
      /** @type {HTMLImageElement} */
      this.element;
      imgEl.decoding = 'async';
      imgEl.alt = '';
      imgEl.src = imageSrc;
      imgEl.setAttribute('role', 'presentation');
    }

    this.element.setAttribute('aria-hidden', 'true');
  }
@param {string | false} imageSrc
@param {HTMLElement} container