https://www.fcdallas.com/addon/whitelabel-razor/js/lazyload_js?_t=6902fae3128df034d67dec8038c6d08a

1(function (d, w) {
2  var lazyPictures = [].slice.call(d.querySelectorAll("picture.lazy"));
3  var manageLaziness = function (lazyPicture) {
4    var lazyImage = lazyPicture.querySelector("img");
5    lazyImage.src = lazyImage.getAttribute("data-src");
6    var lazySources = lazyPicture.querySelectorAll("source");
7    for (var j = 0; j < lazySources.length; j++) {
8      var lazySource = lazySources[j];
9      lazySource.srcset = lazySource.getAttribute("data-srcset");
10    }
11    if (w.addEventListener) {
12      var fallbackTimeout = setTimeout(function () {
13        lazyPicture.className = lazyPicture.className.replace("lazy", "");
14      }, 500);
15      lazyImage.addEventListener("load", function () {
16        lazyPicture.className = lazyPicture.className.replace("lazy", "");
17        clearTimeout(fallbackTimeout);
18      });
19      return;
20    }
21    lazyPicture.className = lazyPicture.className.replace("lazy", "");
22  };
23  if ("IntersectionObserver" in w) {
24    var lazyImageObserver = new IntersectionObserver(function (entries, observer) {
25      for (var i = 0; i < entries.length; i++) {
26        var entry = entries[i];
27        if (!entry.isIntersecting) {
28          continue;
29        }
30        var lazyPicture = entry.target;
31        manageLaziness(lazyPicture);
32        lazyImageObserver.unobserve(lazyPicture);
33      }
34    });
35
36    for (var i = 0; i < lazyPictures.length; i++) {
37      var lazyPicture = lazyPictures[i];
38      lazyImageObserver.observe(lazyPicture);
39    }
40  } else {
41    var lazyFallback = function () {
42      for (var x = 0; x < lazyPictures.length; x++) {
43        var lazyPicture = lazyPictures[x];
44        if ((lazyPicture.getBoundingClientRect().top <= w.innerHeight && lazyPicture.getBoundingClientRect().bottom >= 0) && getComputedStyle(lazyPicture).display !== "none") {
45          manageLaziness(lazyPicture);
46        }
47      }
48      if (d.querySelectorAll("picture.lazy").length) {
49        requestAnimationFrame(lazyFallback);
50      }
51    };
52    requestAnimationFrame(lazyFallback);
53  }
54}(document, window));