IntersectionObserver实现图片懒加载的示例

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" data-src='./images/icon1.png'></li>
    <li class="list-item"><img class="list-item-img" alt="loading" data-src='./images/icon2.png'></li>
    <li class="list-item"><img class="list-item-img" alt="loading" data-src='./images/icon3.png'></li>
    <li class="list-item"><img class="list-item-img" alt="loading" data-src='./images/icon4.png'></li>
    <li class="list-item"><img class="list-item-img" alt="loading" data-src='./images/icon5.png'></li>
    <li class="list-item"><img class="list-item-img" alt="loading" data-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:

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