懒加载 

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <title>Document</title>
    <script src="https://cdn.bootcss.com/jquery/1.11.1/jquery.js"></script>
    <style>
        img {
            display: block;
            margin-bottom: 50px;
            width: 400px;
            height: 400px;
        }
    </style>
</head>

<body>
    <img src="default.jpg" data-src="http://ww4.sinaimg.cn/large/006y8mN6gw1fa5obmqrmvj305k05k3yh.jpg" alt="">
    <img src="default.jpg" data-src="http://ww4.sinaimg.cn/large/006y8mN6gw1fa5obmqrmvj305k05k3yh.jpg" alt="">
    <img src="default.jpg" data-src="http://ww1.sinaimg.cn/large/006y8mN6gw1fa7kaed2hpj30sg0l9q54.jpg" alt="">
    <img src="default.jpg" data-src="http://ww1.sinaimg.cn/large/006y8mN6gw1fa7kaed2hpj30sg0l9q54.jpg" alt="">
    <img src="default.jpg" data-src="http://ww4.sinaimg.cn/large/006y8mN6gw1fa5obmqrmvj305k05k3yh.jpg" alt="">
    <img src="default.jpg" data-src="http://ww4.sinaimg.cn/large/006y8mN6gw1fa5obmqrmvj305k05k3yh.jpg" alt="">
    <img src="default.jpg" data-src="http://ww4.sinaimg.cn/large/006y8mN6gw1fa5obmqrmvj305k05k3yh.jpg" alt="">
    <img src="default.jpg" data-src="http://ww4.sinaimg.cn/large/006y8mN6gw1fa5obmqrmvj305k05k3yh.jpg" alt="">
    <img src="default.jpg" data-src="http://ww1.sinaimg.cn/large/006y8mN6gw1fa7kaed2hpj30sg0l9q54.jpg" alt="">
    <img src="default.jpg" data-src="http://ww4.sinaimg.cn/large/006y8mN6gw1fa5obmqrmvj305k05k3yh.jpg" alt="">
    <img src="default.jpg" data-src="http://ww4.sinaimg.cn/large/006y8mN6gw1fa5obmqrmvj305k05k3yh.jpg" alt="">
</body>

<!-- js代码 -->
<script>
    var num = document.getElementsByTagName('img').length;
    var img = document.getElementsByTagName("img");
    var n = 0; //存储图片加载到的位置，避免每次都从第一张图片开始遍历
    lazyload(); //页面载入完毕加载可是区域内的图片
    window.onscroll = lazyload;

    function lazyload() { //监听页面滚动事件
        var seeHeight = document.documentElement.clientHeight; //可见区域高度
        var scrollTop = document.documentElement.scrollTop || document.body.scrollTop; //滚动条距离顶部高度
        for (var i = n; i < num; i++) {
            if (img[i].offsetTop < seeHeight + scrollTop) {
                if (img[i].getAttribute("src") == "default.jpg") {
                    img[i].src = img[i].getAttribute("data-src");
                }
                n = i + 1;
            }
        }
    }
</script>
<!-- jquery代码 -->
<script>
    var n = 0,
        imgNum = $("img").length,
        img = $('img');
    lazyload();
    $(window).scroll(lazyload);

    function lazyload(event) {
        for (var i = n; i < imgNum; i++) {
            if (img.eq(i).offset().top < parseInt($(window).height()) + parseInt($(window).scrollTop())) {
                if (img.eq(i).attr("src") == "default.jpg") {
                    var src = img.eq(i).attr("data-src");
                    img.eq(i).attr("src", src);
                    n = i + 1;
                }
            }
        }
    }
</script>

</html>

 

posted @ 2017-11-30 19:28  a权  阅读(137)  评论(0)    收藏  举报
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