之前写了一篇原生JS轮播，不过是非面向对象的，并且也没有添加上自动轮播。这里来写一下如何优化和进阶。
这里简单地介绍一下之前的代码,这是html结构
<body>
<div class="wrap">
<ul class="pic-group">
<li><img src="./pic1.jpg" alt=""></li>
<li><img src="./pic2.jpg" alt=""></li>
<li><img src="./pic3.jpg" alt=""></li>
<li><img src="./pic4.jpg" alt=""></li>
<li><img src="./pic5.jpg" alt=""></li>
</ul>
<ol class="num-group">
<li class="current">1</li>
<li>2</li>
<li>3</li>
<li>4</li>
<li>5</li>
</ol>
</div>
</body>
css结构
<style type="text/css">
* {
margin: 0;
padding: 0;
}
ul, li {
list-style: none;
}
body {
background-color: #000;
}
.wrap {
position: relative;
border: 8px solid #fff;
margin: 100px auto;
400px;
height: 250px;
overflow: hidden;
}
.pic-group {
position: absolute;
}
.pic-group li img {
display: block;
100%;
height: 100%;
}
.num-group {
position: absolute;
bottom: 5px;
right: 0;
height: 20px;
}
.num-group li {
float: left;
20px;
height: 20px;
line-height: 20px;
font-size: 10px;
margin-right: 10px;
background-color: #089e8a;
color: #eee;
text-align: center;
border-radius: 10px;
cursor: pointer;
opacity: 0.8;
}
.num-group li:hover {
box-shadow: 0 0 18px #000;
}
.num-group li.current {
opacity: 1;
color: #089a8a;
background-color: #000;
}
</style>
JS 结构
const oImage = document.getElementsByClassName("pic-group")[0];
const oNumber = document.getElementsByClassName("num-group")[0];
const numList = oNumber.getElementsByTagName("li");
for (let i = 0; i < numList.length; i++) {
numList[i].onmouseover = () => {
clearNumState();
show(i);
}
}
const clearNumState = () => {
for (const item of numList) {
item.className = "";
}
}
let timer = null;
const show = (index) => {
numList[index].className = "current";
if (timer) clearInterval(timer);
const target = -250 * index;
let now = oImage.offsetTop;
timer = setInterval(() => {
if (now === target) {
clearInterval(timer);
} else {
now += move(target);
oImage.style.top = now + "px";
console.log(oImage.offsetTop);
}
}, 20);
}
const move = (target) => {
// 当前值
const now = oImage.offsetTop;
const differ = target - now;
console.log(differ / 10);
const res = differ > 0 ? Math.ceil(differ / 10) : Math.floor(differ / 10);
return res;
}
进阶1：我们可以通过offsetHeight获取图片元素的高度。好处1是我们的移动函数不用限死。也为后来将其变为通用的一组代码做铺垫。
这里遇到一个不该出现的问题。常常我们看到直接获取高度的时候是 0，原因是：一些元素是根据内容的高度自动调整的，即所谓的自适应高度，它的高度取决于内容的多少。
获取这样的自适应高度元素主要有两种办法
- currentStyle
- offsetHeight
但用在这里我的offsetHeight竟然是0？不是说好了能获取自适应高度的吗！
const oHeight = oImage.getElementsByTagName("li")[0].offsetHeight;
console.log(oHeight); // 0 !!! 0 !!!
经过我的发现，我知道了问题出在这里？JS代码跑完了？但是图片是否加载完毕了呢?
window.onload = function() {
const oT = document.getElementsByClassName("pic-group")[0];
const oI = oT.getElementsByTagName("li");
console.log(oI[0].offsetHeight); // 250
}
图片没有加载完。当然这里还有一个疑问，为什么控制台有了答案？(这个留待以后探究)
https://www.cnblogs.com/hanxingli/p/5513116.html
这里第 5 句 正是解答，图片还在加载中，先执行了代码。
那么，解决方案是什么呢？
我们需要的是等图片加载完后执行JS的办法
http://www.jb51.net/article/79233.htm
思前想后，这只是个简单的轮播，我选择了window.onload，还有一个不太破坏代码的是async/await，可是那需要加载新的库支持，所以这里选择了最开始的window.onload。
进阶2：添加自动轮播，同时，我们也可以发现，clearNumState应该放在show函数里面
const oImage = document.getElementsByClassName("pic-group")[0];
const oNumber = document.getElementsByClassName("num-group")[0];
const numList = oNumber.getElementsByTagName("li");
const imageList = oImage.getElementsByTagName("li");
const oHeight = imageList[0].offsetHeight;
for (let i = 0; i < numList.length; i++) {
numList[i].onmouseover = () => {
// clearNumState();
show(i);
}
}
const clearNumState = () => {
for (const item of numList) {
item.className = "";
}
}
let timer = null;
const show = (index) => {
clearNumState();
numList[index].className = "current";
if (timer) clearInterval(timer);
const target = -oHeight * index;
let now = oImage.offsetTop;
timer = setInterval(() => {
if (now === target) {
clearInterval(timer);
} else {
now += move(target);
oImage.style.top = now + "px";
console.log(oImage.offsetTop);
}
}, 20);
}
const move = (target) => {
const now = oImage.offsetTop;
const differ = target - now;
console.log(differ / 10);
const res = differ > 0 ? Math.ceil(differ / 10) : Math.floor(differ / 10);
return res;
}
let autoTimer = null;
let index = 0;
const auto = () => {
autoTimer = setInterval(() => {
show(index);
index < numList.length - 1 ? index++ : index = 0;
}, 2000);
}
auto();
进阶3：还需要添加上鼠标移动前后的东西
oImage.onmouseover = function() {
if (autoTimer) clearInterval(autoTimer);
}
oImage.onmouseout = function() {
auto();
}
进阶4：细节优化：关于我们若是我们刚好按到当前显示的轮播页，这个时间问题，就跟下面一起写了~
进阶5：最后就是将代码模式变为面向对象的模式，使得同一页面上的多个轮播结构能够一起进行。这里的改动比较大，就直接上代码了。
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
<style type="text/css">
* {
margin: 0;
padding: 0;
}
ul, li {
list-style: none;
}
body {
background-color: #000;
}
.wrap {
position: relative;
border: 8px solid #fff;
margin: 100px auto;
400px;
height: 250px;
overflow: hidden;
}
.pic-group {
position: absolute;
}
.pic-group li img {
display: block;
100%;
height: 100%;
}
.num-group {
position: absolute;
bottom: 5px;
right: 0;
height: 20px;
}
.num-group li {
float: left;
20px;
height: 20px;
line-height: 20px;
font-size: 10px;
margin-right: 10px;
background-color: #089e8a;
color: #eee;
text-align: center;
border-radius: 10px;
cursor: pointer;
opacity: 0.8;
}
.num-group li:hover {
box-shadow: 0 0 18px #000;
}
.num-group li.current {
opacity: 1;
color: #089a8a;
background-color: #000;
}
</style>
</head>
<body>
<div class="wrap">
<ul class="pic-group">
<li><img src="./pic1.jpg" alt=""></li>
<li><img src="./pic2.jpg" alt=""></li>
<li><img src="./pic3.jpg" alt=""></li>
<li><img src="./pic4.jpg" alt=""></li>
<li><img src="./pic5.jpg" alt=""></li>
</ul>
<ol class="num-group">
<li class="current">1</li>
<li>2</li>
<li>3</li>
<li>4</li>
<li>5</li>
</ol>
</div>
</body>
<script type="text/javascript">
var Carousel = function(cname) {
this.init(cname);
}
Carousel.prototype = {
init: function(cname) {
let me = this;
me.oWrap = document.getElementsByClassName(cname)[0];
me.oImage = me.oWrap.getElementsByTagName("ul")[0];
me.imageList = me.oImage.getElementsByTagName("li");
me.imageHeight = me.imageList[0].offsetHeight;
me.oNumber = me.oWrap.getElementsByTagName("ol")[0];
me.numberList = me.oNumber.getElementsByTagName("li");
me.index = 0;
me.moveTimer = null;
me.autoTimer = null;
for (let i = 0; i < me.numberList.length; i++) {
me.numberList[i].onmouseover = function() {
me.index = i;
me.Show(i);
}
}
me.Auto();
me.oImage.onmouseover = function() {
clearInterval(me.autoTimer);
}
me.oImage.onmouseout = function() {
me.Auto();
}
},
Show: function(index) {
let me = this;
me.clearClass(index);
me.Move(index);
},
Move(index) {
let me = this;
let target = -index * me.imageHeight;
let now;
let speed;
if (me.moveTimer) clearInterval(me.moveTimer);
me.moveTimer = setInterval(() => {
now = me.oImage.offsetTop;
speed = (target - now) / 10;
speed = speed > 0 ? Math.ceil(speed) : Math.floor(speed);
now === target ? clearInterval(me.moveTimer) : me.oImage.style.top = now + speed + "px";
}, 20);
},
Auto() {
let me = this;
me.autoTimer = setInterval(() => {
me.index < me.imageList.length - 1 ? me.index++ : me.index = 0;
me.Show(me.index);
}, 2000);
},
clearClass(index) {
let me = this;
for (let i = 0; i < me.numberList.length; i++) {
me.numberList[i].className = "";
}
me.numberList[index].className = "current";
}
}
window.onload = function() {
new Carousel("wrap");
}
</script>
</html>