示例代码如下：
<!DOCTYPE html>
<html>
<head>
<meta name="generator" content="HTML Tidy for HTML5 for Windows version 5.6.0">
<meta charset="UTF-8">
<title>
实现简单的懒加载Demo
</title>
<style>
img {
display: block;
margin-bottom: 50px;
width: 400px;
height: 400px;
}
</style>
<script type="text/javascript" src="./jquery-2.2.0.min.js"></script>
</head>
<body>
<img src="" data-src="WordPress/wp-content/themes/twentyseventeen/assets/images/coffee.jpg" alt="">
<img src="" data-src="WordPress/wp-content/themes/twentyseventeen/assets/images/espresso.jpg" alt="">
<img src="" data-src="WordPress/wp-content/themes/twentyseventeen/assets/images/header.jpg" alt="">
<img src="" data-src="WordPress/wp-content/themes/twentyseventeen/assets/images/sandwich.jpg" alt="">
<img src="" data-src="WordPress/wp-content/themes/twentyseventeen/assets/images/coffee.jpg" alt="">
<img src="" data-src="WordPress/wp-content/themes/twentyseventeen/assets/images/espresso.jpg" alt="">
<img src="" data-src="WordPress/wp-content/themes/twentyseventeen/assets/images/header.jpg" alt="">
<img src="" data-src="WordPress/wp-content/themes/twentyseventeen/assets/images/sandwich.jpg" alt="">
<img src="" data-src="WordPress/wp-content/themes/twentyseventeen/assets/images/coffee.jpg" alt="">
<img src="" data-src="WordPress/wp-content/themes/twentyseventeen/assets/images/espresso.jpg" alt="">
<img src="" data-src="WordPress/wp-content/themes/twentyseventeen/assets/images/header.jpg" alt="">
<img src="" data-src="WordPress/wp-content/themes/twentyseventeen/assets/images/sandwich.jpg" alt="">
<script type="text/javascript">
/*js版*/
/*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;
}
}
}
*/
/*JQ版本*/
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>
</body>
</html>
方法二：
// 先进行一次检查
lazyRender();
function lazyRender () {
jQuery('#detail img').each(function () {
if (checkShow(jQuery(this)) && !isLoaded(jQuery(this)) ){
loadImg(jQuery(this));
}
})
}
var clock; //这里的clock为timeID，
jQuery(window).on('scroll',function () {//当页面滚动的时候绑定事件
if (clock) { // 如果在300毫秒内进行scroll的话，都会被clearTimeout掉，setTimeout不会执行。
// 如果有300毫秒外的操作，会得到一个新的timeID即clock，会执行一次setTimeout,然后保存这次setTimeout的ID，
// 对于300毫秒内的scroll事件，不会生成新的timeID值，所以会一直被clearTimeout掉，不会执行setTimeout.
clearTimeout(clock);
}
//为了不在滚轮滚动过程中就一直判定，设置个 setTimeout,等停止滚动后再去判定是否出现在视野中。
clock = setTimeout(function () {
console.log('运行了一次');
lazyRender();
},300)
})
function checkShow(img) { // 传入一个img的jq对象
var scrollTop = jQuery(window).scrollTop(); //即页面向上滚动的距离
var windowHeight = jQuery(window).height(); // 浏览器自身的高度
//var windowHeight=window.innerHeight || document.documentElement.clientHeight || document.body.clientHeight;
var offsetTop = img.offset().top; //目标标签img相对于document顶部的位置
console.log(scrollTop, windowHeight, offsetTop);
if (offsetTop < (scrollTop + windowHeight) && offsetTop > scrollTop) { //在2个临界状态之间的就为出现在视野中的
return true;
}
return false;
}
function isLoaded (img) {
return img.attr('data-src') === img.attr('src'); //如果data-src和src相等那么就是已经加载过了
}
function loadImg (img) {
console.log(img)
img.attr('src', img.attr('data-src')); // 加载就是把自定义属性中存放的真实的src地址赋给src属性
}