IntersectionObserver实现图片懒加载的示例

程序员文章站 2022-07-06 21:02:58

api： https://developer.mozilla.org/en-us/docs/web/api/intersection_observer_api 直接上源...

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：

IntersectionObserver实现图片懒加载的示例