lazy-loading.js

document.addEventListener('DOMContentLoaded', function () {
        var lazyloadImages = document.querySelectorAll('img.lazy');
        var lazyloadThrottleTimeout;

        function lazyload() {
          if (lazyloadThrottleTimeout) {
            clearTimeout(lazyloadThrottleTimeout);
          }

          lazyloadThrottleTimeout = setTimeout(function () {
            var scrollTop = window.pageYOffset;
            lazyloadImages.forEach(function (img) {
              if (img.offsetTop < window.innerHeight + scrollTop) {
                img.src = img.dataset.src;
                img.classList.remove('lazy');
              }
            });
            if (lazyloadImages.length == 0) {
              document.removeEventListener('scroll', lazyload);
              window.removeEventListener('resize', lazyload);
              window.removeEventListener('orientationChange', lazyload);
            }
          }, 20);
        }

        document.addEventListener('scroll', lazyload);
        window.addEventListener('resize', lazyload);
        window.addEventListener('orientationChange', lazyload);
      });