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老师批语：懒加载, 其实还有一些其它的实现方式, dom结构也不一定只有这一种, 可以试试其它方式来实现
作业1，懒加载原理是利用元素自定义属性来实现，使用判断在可视区里的图片使用一个固定的图片假地址，不在可视区里面的使用真实的地址赋给元素自定义属性来实现。
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>懒加载作业</title>
</head>
<body>
<!--<button>显示</button>-->
<!--<button>隐藏</button>-->
<!--<hr>-->
<!--<div style="width: 600px;height: 240px;background-color: lawngreen">-->
<!--<img src="#" data-src="./ljz.jpg" alt="">;-->
<!--</div>-->
<script>
var container = document.createElement('div');
var frag = document.createDocumentFragment();
for (var i = 1; i <= 12; i++) {
var imgUrl = 'images/'+ i +'.jpg';
var img = document.createElement('img');
img.setAttribute('src', 'images/loading.gif');
img.setAttribute('data-src', imgUrl);
img.setAttribute('style', 'width:300px;height:350px;margin: 5px;');
frag.appendChild(img);
}
container.appendChild(frag);
document.body.insertBefore(container, document.body.firstElementChild);
window.addEventListener('scroll', lazyLoaded, false);
function lazyLoaded() {
var scrollTop = document.documentElement.scrollTop;
var clientHeight = document.documentElement.clientHeight;
var imgArr = Array.prototype.slice.call(document.images, 0);
imgArr.forEach(function (img) {
if (img.offsetTop <= (scrollTop + clientHeight)) {
img.setAttribute('src', img.dataset.src);
}
});
}
// window.addEventListener('load', lazyLoaded, false);
</script>
</body>
</html>点击 "运行实例" 按钮查看在线实例
作业2：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>选项卡作业</title>
<style>
ul,li {
margin: 0;
padding: 0;
list-style: none;
}
a {
text-decoration: none;
}
a:hover {
text-decoration-color: red;
text-decoration-line: underline;
}
.tab-container {
width: 300px;
height: 200px;
}
.tab-nav {
overflow: hidden;
}
.tab-nav ul li {
float: left;
width: 100px;
height: 30px;
line-height: 30px;
text-align: center;
cursor: pointer;
}
.active {
background-color: lightblue;
}
.tab-content .detail{
line-height: 30px;
min-height: 200px;
padding-top: 10px;
display: none;
}
.detail.active {
display: block;
}
</style>
</head>
<body>
<div class="tab-container">
<div class="tab-nav">
<ul>
<li class="active" data-index="1">选项1</li>
<li data-index="2">选项2</li>
</ul>
</div>
<div class="tab-content">
<div class="detail" data-index="1">
<ul>
<li>选项1内容</li>
<li>选项1内容</li>
<li>选项1内容</li>
<li>选项1内容</li>
</ul>
</div>
<div class="detail" data-index="2">
<ul>
<li>选项2内容</li>
<li>选项2内容</li>
<li>选项2内容</li>
<li>选项2内容</li>
</ul>
</div>
</div>
</div>
<script>
var tabnav=document.getElementsByClassName('tab-nav').item(0);
var tablist=tabnav.firstElementChild.children;
var tabarr=Array.prototype.slice.call(tablist);
var detail= document.getElementsByClassName('detail');
var detailArr = Array.prototype.slice.call(detail, 0);
tabnav.addEventListener('click', showDetail, false);
function showDetail(ev) {
tabarr.forEach(function (tab) { tab.classList.remove('active') });
ev.target.classList.add('active');
detailArr.forEach(function (detail) {detail.classList.remove('active')});
detailArr.forEach(function (detail) {
if (detail.dataset.index === ev.target.dataset.index) {
detail.classList.add('active');
}
});
}
</script>
</body>
</html>点击 "运行实例" 按钮查看在线实例
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