需求：图片预加载（打开网页等待1秒左右时间显示图片），也称懒加载
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>自定义数作用 图片懒加载</title>
<style>
.imglist img {
400px;
height: 300px;
border: 1px solid #ccc;
}
</style>
</head>
<body>
<h1>图片懒加载</h1>
<hr>
<div class="imglist">
<img loadpic='../../dist/images_one/1.jpg'>
<img loadpic='../../dist/images_one/2.jpg'>
<img loadpic='../../dist/images_one/3.jpg'>
<img loadpic='../../dist/images_one/4.jpg'>
</div>
<script src="../jquery-3.3.1.js"></script>
<script>
//console.log($('.imglist img').attr('loadpic'))
//单次定时
setTimeout(function(){
$('.imglist img').each(function(index, item){
$(item).attr('src', $(item).attr('loadpic'))
})
}, 2000)
</script>
</body>
</html>