IntersectionObserver实现图片懒加载

2018-06-24 00:23:35来源：未知阅读 ()

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>