JS implementation of image lazy loading tutorial
Image lazy loading,
Idea: When the mouse slides to the height of the corresponding image, the image is loaded;
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title></title>
<style type="text/css">
#div{
width: 575px;
height: auto;
overflow: hidden;
border: red 1px solid;
margin: 0 auto;
/*给该div设置定位*/
position: relative;
}
#div img{
width: 267px;
height: 396px;
margin-left: 10px;
border: 1px solid #000;
}
</style>
<script type="text/javascript">
function getPos(obj){
var l = 0;
var t = 0;
while(obj){
l += obj.offsetLeft;
t += obj.offsetTop;
obj = obj.offsetParent;
}
return {left:l ,top : t}
}
window.onload = window.onscroll = function(){
//获取到img
var aImg = document.getElementsByTagName("img");
//获取到它的scrollTop 值 考虑兼容问题
var oScrollTop = document.documentElement.scrollTop || document.body.scrollTop;
// clientHeight = 上下padding + height
var clientH = document.documentElement.clientHeight;
//循环遍历每一项通过调用获取到每一个i 项对象的top 值
for (var i = 0;i<aImg.length;i++) {
var aImgTop = getPos(aImg[i]).top;
// 当滚动的时候进行判断,看他的滚动的高度加上它的clientHeight 是否比它的 top 值大
// 如果大或等于说明滚动到当前位置可以加载图片
if (oScrollTop + clientH >= aImgTop) {
// 进行图片的加载
aImg[i].src = aImg[i].getAttribute("_src");
}
}
}
</script>
</head>
<body>
<div id="div">
<img _src="../img/1.jpg"/>
<img _src="../img/2.jpg"/>
<img _src="../img/3.jpg"/>
<img _src="../img/4.jpg"/>
<img _src="../img/6.jpg"/>
<img _src="../img/7.jpg"/>
<img _src="../img/1.jpg"/>
<img _src="../img/2.jpg"/>
<img _src="../img/3.jpg"/>
<img _src="../img/4.jpg"/>
<img _src="../img/6.jpg"/>
<img _src="../img/7.jpg"/>
<img _src="../img/3.jpg"/>
<img _src="../img/4.jpg"/>
<img _src="../img/6.jpg"/>
<img _src="../img/7.jpg"/>
</div>
</body>
</html>When Loading mode commonly used when there is a layout similar to waterfall flow
<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") == "") {
img[i].src = img[i].getAttribute("data-src");
}
n = i + 1;
}
}
}
</script><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") == "") {
var src = img.eq(i).attr("data-src");
img.eq(i).attr("src", src);
n = i + 1;
}
}
}
}
</script>The above is the detailed content of JS implementation of image lazy loading tutorial. For more information, please follow other related articles on the PHP Chinese website!
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