Function navigate

public/js/filePreview.js:722–733

(dir)

setNavVisibility(overlay, images.length > 1, images.length > 1);

const navigate = (dir) => {
  if (!overlay.mediaList || overlay.mediaList.length < 2) return;
  overlay.mediaIndex = (overlay.mediaIndex + dir + overlay.mediaList.length) % overlay.mediaList.length;
  const newFile = overlay.mediaList[overlay.mediaIndex].name;
  currentName = newFile;            // keep download button pointing to the right file
  setTitle(overlay, newFile);
  img.dataset.scale = 1;
  img.dataset.rotate = 0;
  img.style.transform = 'scale(1) rotate(0deg)';
  setPreviewLoading(overlay, true, t('loading') || 'Loading...');
  img.src = siblingPreviewUrl(newFile);   // <-- changed
};

    if (images.length > 1) {
      prevBtn.addEventListener('click', (e) => { e.stopPropagation(); navigate(-1); });