为什么设置id的属性值要用className，不能直接
为什么设置id的属性值要用className，不能直接写dot【i】.id=""，className代表什么意思
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>轮播图</title>
<link rel="stylesheet" type="text/css" href="css/背景.css">
<link rel="stylesheet" type="text/css" href="css/按钮.css">
<link rel="stylesheet" type="text/css" href="css/圆点.css">
</head>
<body>
<div class="main" id="main">
<div class="backgroud" id="bg">
<a href="">
<div class="pic pic1 "></div>
</a>
<a href="">
<div class=" pic pic2 dpy"></div>
</a>
<a href="">
<div class=" pic pic3"></div>
</a>
</div>
<a href="" class="button back" id="back"></a>
<a href="" class="button next" id="next"></a>
<div class="dot" id="dot">
<span ></span>
<span></span>
<span></span>
</div>
</div>
<!-- <script type="text/javascript" src="js/javascript.js"></script> -->
<script type="text/javascript" src="js/js1.js"></script>
</body>
</html>
*{
padding: 0px;
margin: 0px;
}
body,html{
padding: 0px;
margin: 0px;
}
.main{
width: 1200px;
height: 460px;
margin: 30px auto;
overflow: hidden;
position: relative;
}
.main .backgroud{
width: 1200px;
height: 460px;
overflow: hidden; /*减掉移除的图片部分*/
position: relative;
}
.main .backgroud a .pic{
background-repeat: no-repeat;
width: 1200px;
height: 460px;
position: absolute;
display: none;
}
.main .backgroud a .pic1{
background-image: url(../img/bg1.jpg);
}
.main .backgroud a .pic2{
background-image: url(../img/bg2.jpg);
}
.main .backgroud a .pic3{
background-image: url(../img/bg3.jpg);
}
.main .backgroud a .dpy{
display: block;
}
.main .button{
width: 40px;
height:80px;
position: absolute;
left: 244px;
top: 50%;
margin-top: -40px;
background: url(../img/arrow.png) no-repeat center center;
}
.main .button:hover{
background-color: black;
opacity: 0.8
}
.main .back{
transform: rotate(180deg);
}
.main .next{
left: auto;
right: 0;
}
.main .dot{
position: absolute;
right: 15px;
bottom: 24px;
}
.main .dot span{
display: inline-block;
width: 12px;
height:12px;
line-height: 12px;
border-radius: 50%;
background: rgba(7,17,27,0.4);
box-shadow: 0 0 0 2px rgba(255,255,255,0.8) inset; /* 设置描边*/
margin-left: 20px;
cursor:pointer;
}
.main .dot .now{
box-shadow: 0 0 0 2px rgba(7,17,27,0.4) inset;
background-color: white;
}
function byId(id) {
return typeof(id)==="string"?document.getElementById(id):id;
}
var timer=null;
var index=0;
var main=byId('main');
var pics=byId(bg).getElementsByTagName("div");
var len=pics.length;
var dot=byId('dot').getElementsByTagName('span');
function changepic(){
showPic();
main.onmouseover=function(){
if(timer){
clearInterval(timer);
}
}
main.onmouseout=function()
{
timer=setInterval(function(){
index++;
if(index>=len){
index=0;
}
console.log(index);
showPic()
},3000);
}
main.onmouseout();
for(var d=0;d<len;d++){
dot[d].id=d;
dot[d].onclick=function(){
index=this.id;
howPic();
}
}
}
function showPic(){
for(var i=0;i<len;i++){
pics[i].style.display="none";
dot[i].className="";
}
pics[index].style.display="block";
dot[index].className="now";
}
changepic();
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