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How to use IntersectionObserver to implement lazy loading of images

一个新手Original: 2017-09-29 09:34:271838browse

API:

https://developer.mozilla.org/en-US/docs/Web/API/Intersection_Observer_API

Go directly to the source code ：

<!DOCTYPE html><html>
    <header>
        <style>
            .list-item{
                height: 400px; 
                margin: 5px; 
                background-color: lightblue; 
                list-style: none;
            }
        </style>
    </header>
    <body>
        <li class="list-item"><img class="list-item-img" alt="loading" src=&#39;./images/icon1.png&#39;></li>
        <li class="list-item"><img class="list-item-img" alt="loading" src=&#39;./images/icon2.png&#39;></li>
        <li class="list-item"><img class="list-item-img" alt="loading" src=&#39;./images/icon3.png&#39;></li>
        <li class="list-item"><img class="list-item-img" alt="loading" src=&#39;./images/icon4.png&#39;></li>
        <li class="list-item"><img class="list-item-img" alt="loading" src=&#39;./images/icon5.png&#39;></li>
        <li class="list-item"><img class="list-item-img" alt="loading" src=&#39;./images/icon6.png&#39;></li>

        <script>
            var observer = new IntersectionObserver(function(changes) {
                console.log(changes);
                changes.forEach(function(element, index) {                    // statements
                    if (element.intersectionRatio > 0 && element.intersectionRatio <= 1) {
                        element.target.src = element.target.dataset.src;
                    }
                });
            });            
            function addObserver() {                
                  var listItems = document.querySelectorAll(&#39;.list-item-img&#39;);
                listItems.forEach(function(item) {
                    observer.observe(item);
                });
            }

            addObserver();        
       </script>
    </body>
  </html>

After running the code, I found that when the scroll axis is scrolled, the corresponding action will only be triggered when the 25edfb22a4f469ecb59f1190150159c6 area is fully displayed. HTTP request to download the image.

Compatible browsers:

desktop:

Mobile：

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