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如何利用IntersectionObserver实现图片懒加载

来源：爱玩科技网

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：

Mobile：