Listing_11.6.js

// Activates the image gallery.
// The main task is to attach an event listener to each image in the gallery
// and respond appropriately on click.
function activateGallery() {
  let thumbnails = document.querySelectorAll("#gallery-thumbs > ??? > ???");
  let mainImage  = document.querySelector("#gallery-photo img");
  .
  .
  .
}