Custom downloading image in PhotoSwipe.js

//at the start of the document
var downloadIndex = 0;

//in initPhotoSwipeFromDOM function after  gallery.listen('imageLoadComplete') event
gallery.listen('beforeChange', function() {
  downloadIndex +=1;
  console.log(downloadIndex)
  ;});

(function() {
var pswpElement = document.querySelectorAll('.pswp')[0];
if (pswpElement) {
  var gallerySelector = '.masonry';
  var initPhotoSwipeFromDOM = function(gallerySelector) {

      // parse slide data (url, title, size ...) from DOM elements
      // (children of gallerySelector)
      var parseThumbnailElements = function(el) {
        var thumbElements = $(el).find('.masonry-item').toArray(),
          numNodes = thumbElements.length,
          items = [],
          figureEl,
          linkEl,
          size,
          imgEl,
          item;

          for (var i = 0; i < numNodes; i++) {

      figureEl = thumbElements[i]; // <figure> element

      // include only element nodes
      if (figureEl.nodeType !== 1) {
        continue;
      }

      linkEl = figureEl.children[0]; // <a> element
      imgEl = linkEl.children[0]; // <img>

      size = linkEl.getAttribute('data-size');
      size = size && size.split('x');

      // create slide object
      item = {
        src: linkEl.getAttribute('href'),
        w: size && parseInt(size[0], 10) || imgEl.width,
        h: size && parseInt(size[1], 10) || imgEl.height,
        title: linkEl.getAttribute('data-caption'),
        hqImage: linkEl.getAttribute('original-image')
      };

      if (figureEl.children.length > 1) {
        item.title = figureEl.children[1].innerHTML;
      }

      if (linkEl.children.length > 0) {
        // <img> thumbnail element, retrieving thumbnail url
        item.msrc = linkEl.children[0].getAttribute('src');
      }

      item.el = figureEl; // save link to element for getThumbBoundsFn
      items.push(item);
    }

    return items;
  };

  // find nearest parent element
  var closest = function closest(el, fn) {
    return el && (fn(el) ? el : closest(el.parentNode, fn));
  };

  // triggers when user clicks on thumbnail
  var onThumbnailsClick = function(e) {
    e = e || window.event;

    var eTarget = e.target || e.srcElement;

    // find root element of slide
    var clickedListItem = closest(eTarget, function(el) {
      return (el.className && el.className.toUpperCase() === 'MASONRY-ITEM');
    });

    if (!clickedListItem) {
      return;
    }

    if (e.preventDefault) {
      e.preventDefault();
    } else {
      e.returnValue = false;
    }

            // find index of clicked item by looping through all child nodes
            // alternatively, you may define index via data- attribute
            var clickedGallery = $(clickedListItem).closest(gallerySelector)[0],
              childNodes = $(clickedGallery).find('.masonry-item').toArray(),
              numChildNodes = childNodes.length,
              nodeIndex = 0,
              index;

                      for (var i = 0; i < numChildNodes; i++) {
                        if (childNodes[i].nodeType !== 1) {
                          continue;
                        }

                        if (childNodes[i] === clickedListItem) {
                          index = nodeIndex;
                          break;
                        }
                        nodeIndex++;
                      }



                      if (index >= 0) {
                        // open PhotoSwipe if valid index found
                        openPhotoSwipe(index, clickedGallery);
                      }
                      return false;
                    };

                    // parse picture index and gallery index from URL (#&pid=1&gid=2)
                    var photoswipeParseHash = function() {
                      var hash = window.location.hash.substring(1),
                        params = {};

                      if (hash.length < 5) {
                        return params;
                      }

                      var vars = hash.split('&');
                      for (var i = 0; i < vars.length; i++) {
                        if (!vars[i]) {
                          continue;
                        }
                        var pair = vars[i].split('=');
                        if (pair.length < 2) {
                          continue;
                        }
                        params[pair[0]] = pair[1];
                      }

                      if (params.gid) {
                        params.gid = parseInt(params.gid, 10);
                      }

                      return params;
                    };


                    var openPhotoSwipe = function(index, galleryElement, disableAnimation, fromURL) {
                      var pswpElement = document.querySelectorAll('.pswp')[0],
                        gallery,
                        options,
                        items;

                      items = parseThumbnailElements(galleryElement);
                      // define options (if needed)
                      options = {

                        // define gallery index (for URL)
                        galleryUID: galleryElement.getAttribute('data-pswp-uid'),

                        getThumbBoundsFn: function(index) {
                          // See Options -> getThumbBoundsFn section of documentation for more info
                          var thumbnail = items[index].el.getElementsByTagName('img')[0], // find thumbnail
                            pageYScroll = window.pageYOffset || document.documentElement.scrollTop,
                            rect = thumbnail.getBoundingClientRect();

                          return {
                            x: rect.left,
                            y: rect.top + pageYScroll,
                            w: rect.width
                          };
                        },
                        bgOpacity:0.85,
                        timeToIdle: 3000,
                        shareButtons: [
                          {id:'facebook', label:'Share on Facebook', url:'https://www.facebook.com/sharer/sharer.php?u={{url}}'},
                          {id:'twitter', label:'Tweet', url:'https://twitter.com/intent/tweet?text={{text}}&url={{url}}'},
                          {id:'pinterest', label:'Pin it', url:'http://www.pinterest.com/pin/create/button/?url={{url}}&media={{image_url}}&description={{text}}'},
                          {id:'vk', label:'Share on VK', url:'https://vk.com/share.php?url={{url}}'},
                          {id:'download', label:'Download HQ image', url:items[0].hqImage, download:true } //items[index].hqImage
                        ],
                        closeOnScroll:false,

                      };

                      // PhotoSwipe opened from URL
                      if (fromURL) {
                        if (options.galleryPIDs) {
                          // parse real index when custom PIDs are used
                          // http://photoswipe.com/documentation/faq.html#custom-pid-in-url
                          for (var j = 0; j < items.length; j++) {
                            if (items[j].pid == index) {
                              options.index = j;
                              break;
                            }
                          }
                        } else {
                          // in URL indexes start from 1
                          options.index = parseInt(index, 10) - 1;
                        }
                      } else {
                        options.index = parseInt(index, 10);
                      }

                      // exit if index not found
                      if (isNaN(options.index)) {
                        return;
                      }

                      if (disableAnimation) {
                        options.showAnimationDuration = 0;
                      }

                      // Pass data to PhotoSwipe and initialize it
                      var gallery = new PhotoSwipe(pswpElement, PhotoSwipeUI_Default, items, options);

                      gallery.listen('imageLoadComplete', function(index, item) {
                        var linkEl = item.el.children[0];
                        var img = item.container.children[0];
                        if (!linkEl.getAttribute('data-size')) {
                          linkEl.setAttribute('data-size', img.naturalWidth + 'x' + img.naturalHeight);
                          item.w = img.naturalWidth;
                          item.h = img.naturalHeight;
                          gallery.invalidateCurrItems();
                          gallery.updateSize(true);
                        }
                      });

                      gallery.init();
                    };

                    // loop through all gallery elements and bind events
                    var galleryElements = document.querySelectorAll(gallerySelector);

                    for (var i = 0, l = galleryElements.length; i < l; i++) {
                      galleryElements[i].setAttribute('data-pswp-uid', i + 1);
                      galleryElements[i].onclick = onThumbnailsClick;
                    }

                    // Parse URL and open gallery if it contains #&pid=3&gid=1
                    var hashData = photoswipeParseHash();
                    if (hashData.pid && hashData.gid) {
                      openPhotoSwipe(hashData.pid, galleryElements[hashData.gid - 1], true, true);
                    }
                  };

                  // execute above function
                  initPhotoSwipeFromDOM(gallerySelector);
                }
              })();

<!--for the grid layout I use Isotope.js-->
<div class="masonry">
  <div class="masonry-sizer"></div>
    <div class="masonry-item">
      <a href="../../img/paintings/Graia.jpg" data-caption="Graia<br>1" original-image='../../img/original/paintings/Graia.jpg'>
        <img class="masonry-content" src="../../img/previews/paintings/Graia.webp">
      </a>
  </div>
</div>

getImageURLForShare: function( /* shareButtonData */ ) {
				return pswp.currItem.src || '';

getImageURLForShare: function( /* shareButtonData */ ) {
				return pswp.currItem.hqImage || '';