https://www.mailboxvalidator.com/includes/js/lazyloadsprite.js

1document.addEventListener("DOMContentLoaded", function() {
2  let lazySprites = [].slice.call(document.querySelectorAll("img.mainpage_ico"));
3  let active = false;
4
5  const lazyLoadSprite = function() {
6    if (active === false) {
7      active = true;
8
9      setTimeout(function() {
10        lazySprites.forEach(function(lazySprite) {
11          if ((lazySprite.getBoundingClientRect().top <= window.innerHeight && lazySprite.getBoundingClientRect().bottom >= 0) && getComputedStyle(lazySprite).display !== "none") {
12            lazySprite.classList.add(lazySprite.dataset.src);
13            // lazySprite.srcset = lazySprite.dataset.srcset;
14            // lazySprite.classList.remove("lazy");
15
16            lazySprites = lazySprites.filter(function(image) {
17              return image !== lazySprite;
18            });
19
20            if (lazySprites.length === 0) {
21              document.removeEventListener("scroll", lazyLoadSprite);
22              window.removeEventListener("resize", lazyLoadSprite);
23              window.removeEventListener("orientationchange", lazyLoadSprite);
24            }
25          }
26        });
27
28        active = false;
29      }, 200);
30    }
31  };
32
33  document.addEventListener("scroll", lazyLoadSprite);
34  window.addEventListener("resize", lazyLoadSprite);
35  window.addEventListener("orientationchange", lazyLoadSprite);
36});