d = firstCallback ? 'image_id' : 'second_id';
        checkImage(entry, url, id, size, beforeLoad);
        if (firstCallback) {
          const img = document.createElement('img');
          img.src = '/images/black-rectangle.png';
          img.id = 'second_id';
          beforeLoad = performance.now();
          document.getElementById('image_div').appendChild(img);
          firstCallback = false;
          return;
        } else {
          t.done();
        }
      })
    );
    observer.observe({type