<div id="container">
<img src="https://ik.imagekit.io/demo/img/image1.jpeg?tr=w-400,h-300" />
<img src="https://ik.imagekit.io/demo/img/image2.jpeg?tr=w-400,h-300" />
<img src="https://ik.imagekit.io/demo/img/image3.jpg?tr=w-400,h-300" />
<img class="lazy" data-src="https://ik.imagekit.io/demo/img/image4.jpeg?tr=w-400,h-300" />
<img class="lazy" data-src="https://ik.imagekit.io/demo/img/image5.jpeg?tr=w-400,h-300" />
<img class="lazy" data-src="https://ik.imagekit.io/demo/img/image6.jpeg?tr=w-400,h-300" />
<img class="lazy" data-src="https://ik.imagekit.io/demo/img/image7.jpeg?tr=w-400,h-300" />
<img class="lazy" data-src="https://ik.imagekit.io/demo/img/image8.jpeg?tr=w-400,h-300" />
<img class="lazy" data-src="https://ik.imagekit.io/demo/img/image9.jpeg?tr=w-400,h-300" />
<img class="lazy" data-src="https://ik.imagekit.io/demo/img/image10.jpeg?tr=w-400,h-300" />
</div>

img {
  background: #F1F1FA;
  width: 400px;
  height: 300px;
  display: block;
  margin: 10px auto;
  border: 0;
}

#container {
  height: 420px;
  overflow-y: scroll;
}

$(document).ready(function() {
  var lazyloadImages;    

  if ("IntersectionObserver" in window) {
    lazyloadImages = document.querySelectorAll(".lazy");
    var imageObserver = new IntersectionObserver(function(entries, observer) {
      console.log(observer);
      entries.forEach(function(entry) {
        if (entry.isIntersecting) {
          var image = entry.target;
          image.src = image.dataset.src;
          image.classList.remove("lazy");
          imageObserver.unobserve(image);
        }
      });
    }, {
      root: document.querySelector("#container"),
      rootMargin: "0px 0px 500px 0px"
    });

    lazyloadImages.forEach(function(image) {
      imageObserver.observe(image);
    });
  } else {  
    var lazyloadThrottleTimeout;
    lazyloadImages = $(".lazy");
    
    function lazyload () {
      if(lazyloadThrottleTimeout) {
        clearTimeout(lazyloadThrottleTimeout);
      }    

      lazyloadThrottleTimeout = setTimeout(function() {
          var scrollTop = $(window).scrollTop();
          lazyloadImages.each(function() {
              var el = $(this);
              if(el.offset().top < window.innerHeight + scrollTop + 500) {
                var url = el.attr("data-src");
                el.attr("src", url);
                el.removeClass("lazy");
                lazyloadImages = $(".lazy");
              }
          });
          if(lazyloadImages.length == 0) { 
            $(document).off("scroll");
            $(window).off("resize");
          }
      }, 20);
    }

    $(document).on("scroll", lazyload);
    $(window).on("resize", lazyload);
  }
})