懒加载
代码实现
html
<!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>Document</title>
<link rel="stylesheet" href="lazyload.css">
</head>
<body>
<div class="image-list">
<img src="" class="image-item" lazyload="true" data-original="https://img.alicdn.com/imgextra/i2/252339290/TB29PYUXnIlyKJjSZFrXXXn2VXa_!!252339290-0-beehive-scenes.jpg_180x180xzq90.jpg_.webp" alt="">
<img src="" class="image-item" lazyload="true" data-original="https://img.alicdn.com/imgextra/i4/2260152888/O1CN01vw2e251XCkJr0VPZU_!!2260152888-0-beehive-scenes.jpg_250x250xz.jpg" alt="">
<img src="" class="image-item" lazyload="true" data-original="https://img.alicdn.com/imgextra/i3/24687421/TB2Xg1izsyYBuNkSnfoXXcWgVXa_!!24687421-0-beehive-scenes.jpg_250x250xz.jpg" alt="">
<img src="" class="image-item" lazyload="true" data-original="https://img.alicdn.com/imgextra/i4/890151842/TB2II1mnZbI8KJjy1zdXXbe1VXa_!!890151842-0-beehive-scenes.jpg_250x250xz.jpg" alt="">
<img src="" class="image-item" lazyload="true" data-original="https://img.alicdn.com/imgextra/i2/2096513830/TB2l1W0kRnTBKNjSZPfXXbf1XXa_!!2096513830-0-beehive-scenes.jpg_250x250xz.jpg" alt="">
<img src="" class="image-item" lazyload="true" data-original="https://img.alicdn.com/imgextra/i3/2586222636/TB2RDGrpqAoBKNjSZSyXXaHAVXa_!!2586222636-0-daren.jpg_250x250xz.jpg" alt="">
<img src="" class="image-item" lazyload="true" data-original="https://img.alicdn.com/imgextra/i2/1870112525/TB2Ae.xbOwIL1JjSZFsXXcXFFXa_!!1870112525-2-beehive-scenes.png_250x250xz.jpg" alt="">
<img src="" class="image-item" lazyload="true" data-original="https://img.alicdn.com/imgextra/i2/2194952831/TB2PwWty7qvpuFjSZFhXXaOgXXa_!!2194952831-0-beehive-scenes.jpg_250x250xz.jpg" alt="">
</div>
<script src="./lazyload.js"></script>
</body>
</html>css
.image-item {
display: inline-block;
width: 100%;
height: 300px;
background: gray;
}js
var viewHeight = document.documentElement.clientHeight;
function lazyload() {
var imgs = document.querySelectorAll('img[data-original][lazyload]');
imgs.forEach(item => {
if (item.dataset.original == '') {
return;
}
var rect = item.getBoundingClientRect();
if (rect.bottom >= 0 && rect.top < viewHeight) {
var img = new Image();
img.src = item.dataset.original;
console.log(img.src)
img.onload = function() {
item.src = img.src;
}
item.removeAttribute('data-original');
item.removeAttribute('lazyload')
}
})
}
lazyload();
document.addEventListener('scroll', lazyload)效果
- 蓝色为已经请求加载的图片
- 红色为还没有请求加载的图片
默认打开，没有操作前
向下滚动前
向下滚动后
冷门属性
ocument.addEventListener（事件监听）
document.addEventListener('scroll', function() {
console.log('aa')
})
dataset
用`dataset.original`获取`data-original` 的属性 img.onload
事件在图片加载完成后立即执行
getBoundingClientRect
用于获取某个元素相对于视窗的位置集合。集合中有top, right, bottom, left等属性
文档各种高度
document.documentElement.clientHeight:视口的大小document.documentElement.scrollHeight:文档的大小document.documentElement.offsetHeight:文档的大小
预加载
标签
<img style="display:none;" src="https://img.alicdn.com/imgextra/i4/2260152888/O1CN01vw2e251XCkJr0VPZU_!!2260152888-0-beehive-scenes.jpg_250x250xz.jpg" alt="">new Image()
var image = new Image();
image.src = 'https://img.alicdn.com/imgextra/i4/2260152888/O1CN01vw2e251XCkJr0VPZU_!!2260152888-0-beehive-scenes.jpg_250x250xz.jpg';<script src='./myPreload.js'></script>xml
<script src="https://cdn.bootcss.com/PreloadJS/1.0.1/preloadjs.min.js"></script>
<script>
var queue = new createjs.LoadQueue();
queue.installPlugin(createjs.Sound);
queue.on("complete", handleComplete, this);
queue.loadFile({
id: "sound",
src: "http://path/to/sound.mp3"
});
queue.loadManifest([{
id: "myImage",
src: "path/to/myImage.jpg"
}]);
function handleComplete() {
createjs.Sound.play("sound");
var image = queue.getResult("myImage");
document.body.appendChild(image);
}
</script>
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