如何利用IntersectionObserver实现图片懒加载

一个新手 原创: 2017-09-29 09:34:27 1359浏览

API：

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

直接上源码：

<!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='./images/icon1.png'></li>
        <li class="list-item"><img class="list-item-img" alt="loading" src='./images/icon2.png'></li>
        <li class="list-item"><img class="list-item-img" alt="loading" src='./images/icon3.png'></li>
        <li class="list-item"><img class="list-item-img" alt="loading" src='./images/icon4.png'></li>
        <li class="list-item"><img class="list-item-img" alt="loading" src='./images/icon5.png'></li>
        <li class="list-item"><img class="list-item-img" alt="loading" src='./images/icon6.png'></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('.list-item-img');
                listItems.forEach(function(item) {
                    observer.observe(item);
                });
            }

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

运行代码后发现，当滚动滚动轴时，只有当<li>区域完全显示出来后才会触发相应的下载图片的http请求。

兼容浏览器：

desktop：