JS实现图片懒加载
2021-02-23 本文已影响0人
Thesand
第一种
<!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(imgs) {
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])) {
imgs[i].src = imgs[i].getAttribute('data-src');
}
}
}
window.onload = window.onscroll = function () { //onscroll()在滚动条滚动的时候触发
lazyLoad(imgs);
}
</script>
</html>
第二种
var imgs = document.querySelectorAll('img');
//用来判断bound.top<=clientHeight的函数，返回一个bool值
function isIn(el) {
var bound = el.getBoundingClientRect();
var clientHeight = window.innerHeight;
return bound.top <= clientHeight;
}
//检查图片是否在可视区内，如果不在，则加载
function check() {
Array.from(imgs).forEach(function(el){
if(isIn(el)){
loadImg(el);
}
})
}
function loadImg(el) {
if(!el.src){
var source = el.dataset.src;
el.src = source;
}
}
window.onload = window.onscroll = function () { //onscroll()在滚动条滚动的时候触发
check();
}
