当页面需要请求大量图片时，会耗费大量的数据，使用懒加载，跨域提高用户的体验
js代码
var num = document.getElementsByTagName('img').length;
var img = document.getElementsByTagName("img");
// 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
var n = 0;
// 页面载入完毕加载可视区域内的图片
lazyLoad();
window.onscroll = lazyLoad;
// 监听页面滚动事件
function lazyLoad() {
// 可见区域高度
var seeHeight = document.documentElement.clientHeight;
// 滚动条距离顶部高度
var scrollTop = document.documentElement.scrollTop || document.body.scrollTop;
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;
}
}
}
完整的代码如下
<!DOCTYPE HTML>
<html>
<head>
<meta charset="UTF-8">
<title>页面懒加载</title>
<style>
img {
display: block;
margin: 0 auto 50px;
960px;
height: 540px;
}
</style>
</head>
<body>
<img src="default.jpg" data-src="http://ww1.sinaimg.cn/large/005ODVHQgy1fuzutb8xegj31hc0u0k77.jpg" alt="">
<img src="default.jpg" data-src="http://ww1.sinaimg.cn/large/005ODVHQgy1fuzutz6y29j31hc0u0ak4.jpg" alt="">
<img src="default.jpg" data-src="http://ww1.sinaimg.cn/large/005ODVHQgy1fuzuu8igyyj31hc0u0qgv.jpg" alt="">
<img src="default.jpg" data-src="http://ww1.sinaimg.cn/large/005ODVHQgy1fuzuug47wrj31hc0u0k2q.jpg" alt="">
<img src="default.jpg" data-src="http://ww1.sinaimg.cn/large/005ODVHQgy1fuzuuowb0hj31hc0u0akx.jpg" alt="">
<img src="default.jpg" data-src="http://ww1.sinaimg.cn/large/005ODVHQgy1fuzuuyjapsj31hc0u0ths.jpg" alt="">
<img src="default.jpg" data-src="http://ww1.sinaimg.cn/large/005ODVHQgy1fuzutb8xegj31hc0u0k77.jpg" alt="">
<img src="default.jpg" data-src="http://ww1.sinaimg.cn/large/005ODVHQgy1fuzutz6y29j31hc0u0ak4.jpg" alt="">
<img src="default.jpg" data-src="http://ww1.sinaimg.cn/large/005ODVHQgy1fuzuu8igyyj31hc0u0qgv.jpg" alt="">
<img src="default.jpg" data-src="http://ww1.sinaimg.cn/large/005ODVHQgy1fuzuug47wrj31hc0u0k2q.jpg" alt="">
<img src="default.jpg" data-src="http://ww1.sinaimg.cn/large/005ODVHQgy1fuzuuowb0hj31hc0u0akx.jpg" alt="">
<img src="default.jpg" data-src="http://ww1.sinaimg.cn/large/005ODVHQgy1fuzuuyjapsj31hc0u0ths.jpg" alt=""> <img
src="default.jpg" data-src="http://ww1.sinaimg.cn/large/005ODVHQgy1fuzutb8xegj31hc0u0k77.jpg" alt="">
<img src="default.jpg" data-src="http://ww1.sinaimg.cn/large/005ODVHQgy1fuzutz6y29j31hc0u0ak4.jpg" alt="">
<img src="default.jpg" data-src="http://ww1.sinaimg.cn/large/005ODVHQgy1fuzuu8igyyj31hc0u0qgv.jpg" alt="">
<img src="default.jpg" data-src="http://ww1.sinaimg.cn/large/005ODVHQgy1fuzuug47wrj31hc0u0k2q.jpg" alt="">
<img src="default.jpg" data-src="http://ww1.sinaimg.cn/large/005ODVHQgy1fuzuuowb0hj31hc0u0akx.jpg" alt="">
<img src="default.jpg" data-src="http://ww1.sinaimg.cn/large/005ODVHQgy1fuzuuyjapsj31hc0u0ths.jpg" alt="">
</body>
<script>
var num = document.getElementsByTagName('img').length;
var img = document.getElementsByTagName("img");
// 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
var n = 0;
// 页面载入完毕加载可视区域内的图片
lazyload();
window.onscroll = lazyload;
// 监听页面滚动事件
function lazyload() {
// 可见区域高度
var seeHeight = document.documentElement.clientHeight;
// 滚动条距离顶部高度
var scrollTop = document.documentElement.scrollTop || document.body.scrollTop;
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>
</html>