<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width,initial-scale=1,minimum-scale=1,maximum-scale=1,user-scalable=no" />
<title></title>
<style type="text/css">
*{ padding: 0; margin: 0;
}
ul,li{ list-style: none; }
img{ 100%; height: 160px; /* 以下样式是为了做渐变效果 */
opacity: 0; transition: opacity 2s;
}
img[src]{ opacity: 1; }
</style>
</head>
<body>
<ul>
<li><img data-src="//cdn.attach.qdfuns.com/promotion/201704/22/103505xf3q3n3nnpy03pd3.png"/></li>
<li><img data-src="//cdn.attach.qdfuns.com/promotion/201704/22/103505xf3q3n3nnpy03pd3.png"/></li>
<li><img data-src="//cdn.attach.qdfuns.com/promotion/201704/22/103505xf3q3n3nnpy03pd3.png"/></li>
<li><img data-src="//cdn.attach.qdfuns.com/promotion/201704/22/103505xf3q3n3nnpy03pd3.png"/></li>
<li><img data-src="//cdn.attach.qdfuns.com/promotion/201704/22/103505xf3q3n3nnpy03pd3.png"/></li>
<li><img data-src="//cdn.attach.qdfuns.com/promotion/201704/22/103505xf3q3n3nnpy03pd3.png"/></li>
<li><img data-src="//cdn.attach.qdfuns.com/promotion/201704/22/103505xf3q3n3nnpy03pd3.png"/></li>
</ul>
<script type="text/javascript">
/*
* 图片懒加载的思路
* 1、提前给所有图片设置宽和高用来占位
* 2、不设置图片的src属性，而是自定义一个data-src属性来存储图片的路径
* 3、判断当前屏幕的位置（图片的top值和屏幕底部的值），来进行是否显示
* 图片，如果需要显示的话，把data-src的值给src
*/
//获取所有图片
var imgs = document.querySelectorAll("img"); //设置滚动事件
window.onscroll = lazyloadFn; //屏幕的高度
var sh = window.innerHeight; console.log(sh); //刚进来需要先调用下
lazyloadFn(); //图片懒加载的方法
function lazyloadFn () { //获取滚动的距离
var st = document.body.scrollTop; //计算滚动中的底部的值
var sn = sh + st; //循环所有的图片
for (var i = 0; i < imgs.length; i++) {
if (imgs[i].offsetTop <= sn) {
imgs[i].src = imgs[i].getAttribute("data-src");
}
}
}
</script>
</body>
</html>