原生JS实现的自动轮播图功能详解

<div id="banner">
  <ul id="img-list">
    <li><img src="images/banner1.png" alt="1"/></li>
    <li><img src="images/banner2.jpg" alt="2"/></li>
    <li><img src="images/banner3.png" alt="3"/></li>
  </ul>
  <div id="list">
    <span index="1" class="on"></span>
    <span index="2"></span>
    <span index="3"></span>
  </div>
</div>

#banner {
  width:100%;
  padding:0;
  clear: both;
  position: relative;
  height: 400px;
  z-index:1;
}
#img-list {
  display: block;
  width:5760px;
  height: 400px;
  overflow: hidden;
  z-index:1;
  position: relative;
}
#img-list li{
  float: left;
  width:100%;
  height: 400px;
  overflow: hidden;
  /* position: absolute;
  top:0;
  left:0; */
  z-index: 2;
}
#list {
  width:100%;
  height:18px;
  text-align: center;
  position: absolute;
  bottom: 10px;
  z-index: 100;
}
#list > span {
  width:18px;
  height: 18px;
  overflow: hidden;
  display: inline-block;
  margin:0 2px;
  background: url(../images/yuan.png);
  cursor: pointer;
}
#list .on {
  background: url(../images/huanyu.png);
}

var banner=document.getElementById('banner');
var imglist=document.getElementById('img-list').getElementsByTagName("li");
var list=document.getElementById('list').getElementsByTagName('span');
var index=0;
var timer=null;
//设置自动播放函数
function autoPlay () {
   if (++index >= imglist.length) {index = 0};
   changeImg(index);
}
// 鼠标划过整个容器时停止自动播放
banner.onmouseover = function () {
   clearInterval(timer);
}
// 鼠标离开整个容器时继续播放至下一张
banner.onmouseout=function(){
   timer=setInterval(autoPlay,2000);
}
// 定义并调用自动播放函数
timer = setInterval(autoPlay, 2000);
接着定义图片的切换函数
// 定义图片切换函数
function changeImg (curIndex) {
   for (var i = 0; i < imglist.length; i++) {
     imglist[i].style.display = "none";
     list[i].className = "";
   }
   imglist[curIndex].style.display = "block";
   list[curIndex].className = "on";
}

for (var i = 0; i < list.length; i++) {
 list[i].index=i;
 list[i].onmouseover = function () {
 clearInterval(timer);
 changeImg(this.index);
};