code: function doReveal(el) {
        var orig = el.getAttribute('src') || false;
  
        el.addEventListener('error', function handler(e) {
          // on error put back the original image if available (usually a placeholder)
          console.log('error loading image', e);
          if (orig) {
            el.setAttribute('src', orig);
          }
          el.removeEventListener('error', handler); // hate this.
        });
  
        var src = el.getAttribute('data-src');
        if (src) {
          el.setAttribute('src', src);
          addClass(el);
          return;
        }
        src = el.getAttribute('data-bkg');
        if (src) {
          el.style.backgroundImage = 'url("' + src + '")';
          addClass(el);
          return;
        }
      }
docs: set the image src or background attribute