图片懒加载-蒲公英云

图片懒加载

青旅半醒 2022-11-16 13:41 485阅读 0赞

watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3NvbmdsZjUyMQ_size_16_color_FFFFFF_t_70

如果：offsetTop-scrollTop<clientHeight，则图片进入了可视区内，则被请求；

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>图片懒加载</title>
    <style>
        img {
            display: block;
            width: 100%;
            height: 300px;
            margin-bottom: 20px;
        }
    </style>
</head>
<body>
    <img data-src="./images/1.jpg" alt="">
    <img data-src="./images/2.jpg" alt="">
    <img data-src="./images/3.jpg" alt="">
    <img data-src="./images/4.jpg" alt="">
    <img data-src="./images/5.jpg" alt="">
    <img data-src="./images/6.jpg" alt="">
    <img data-src="./images/7.jpg" alt="">
    <img data-src="./images/8.jpg" alt="">
    <img data-src="./images/9.jpg" alt="">
    <img data-src="./images/10.jpg" alt="">
    <img data-src="./images/1.jpg" alt="">
    <img data-src="./images/2.jpg" alt="">
</body>
<script>
        var imgs = document.querySelectorAll('img');
        //offsetTop是元素与offsetParent的距离，循环获取直到页面顶部
        function getTop(e) {
            var T = e.offsetTop;
            while(e = e.offsetParent) {
                T += e.offsetTop;
            }
            return T;
        }
        function lazyLoad() {
            var H = document.documentElement.clientHeight;//获取可视区域高度
            var S = document.documentElement.scrollTop || document.body.scrollTop;
            for (var i = 0; i < imgs.length; i++) {
                if (H + S > getTop(imgs[i])) { // clientHeight + scrollTop > offsetTop
                    imgs[i].src = imgs[i].getAttribute('data-src');
                }
            }
        }
          function throttling(callback, delay = 1000) {
                let timer = null
                return function () {
                  if (timer) return
                  timer = setTimeout(() => {
                    callback()
                    timer = null
                  }, delay)
            }
          }
        window.onload = window.onscroll = throttling(lazyLoad);
</script>
</html>