基于JavaScript实现带缩略图的轮播效果

<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<style>
*{padding:0;margin:0;}
#content {width:400px;height:500px;margin:10px auto;position:relative;border:1px solid #000;color:red;font-size:20px;}
#title, #bottom{position:absolute;width:400px;height:30px;line-height:30px;text-align:center;font-size:20px;background:#f1f1f1;}
#bottom{bottom:0;cursor:pointer;}
#bottom span{display:inline-block;width:15px;height:15px;border-radius:15px;background:#000;text-align:center;line-height:15px;position:relative;}
#bottom span.active{background: #FFFF33;}
#bottom span div {position:absolute;width:110px;height:110px;top:-125px;left:-46px;display:none;}
#bottom span div:after{content:'';position:absolute;left:49px;bottom:-12px;border-top:7px solid #fff;border-right:5px solid transparent;border-bottom:5px solid transparent;border-left:5px solid transparent;}
#bottom span img {width:100px;height:100px;border:5px solid #fff;}
#left, #right{position:absolute;width:60px;height:60px;border-radius:60px;line-height:60px;font-size:60px;background:#FFFF66;font-weight:bold;text-align:center;top:50%;margin-top:-25px;color:#fff;cursor:pointer;filter(opacity:70);opacity:0.7;}
#left:hover,#right:hover{filter(opacity:100);opacity:1;}
#left{left:0px;}
#right{right:0px;} 
#img{width:400px;height:500px;}
</style>
<script>
window.onload = function () {
 var bottom = $('bottom'),title = $('title'),
 img = $('img'),left = $('left'),right = $('right');
 var aSpan = bottom.getElementsByTagName('span');
 var aDiv = bottom.getElementsByTagName('div');
 var arr = ['图片一','图片二','图片三', '图片四'];
 var num = 0;
 // 初始化
 picTab();

 // 点击下一张
 right.onclick = function () {
 if (num === aDiv.length - 1) num = -1;
 num++;
 picTab();
 }

 // 点击上一张
 left.onclick = function () {
 if (num === 0) num = aDiv.length;
 num--;
 picTab();
 }

 function picTab() {
 title.innerHTML = arr[num];
 img.src = 'img/' + (num + 1) + '.png';
 for ( var i = 0; i < aSpan.length; i++ ) {
  aSpan[i].className = '';
 }
 aSpan[num].className = 'active';
 }
 // 鼠标移入移出显示缩略图
 for ( var i = 0; i < aSpan.length; i++ ) {
 aSpan[i].index = i;
 aSpan[i].onmouseover = function () {
  aDiv[this.index].style.display = 'block';
 }
 aSpan[i].onmouseout = function () {
  aDiv[this.index].style.display = 'none';
 }
 aSpan[i].onclick = function () {
  num = this.index;
  picTab();
 }
 }
 function $(id) { return document.getElementById(id);}
}
</script>
</head>
<body>
<div id="content">
 <div id="title">带缩略图的轮播</div>
 <div id="left"><</div>
 <div id="right">></div>
 <div id="bottom">
 <span><div><img src="img/1.png"/></div></span>
 <span><div><img src="img/2.png"/></div></span>
 <span><div><img src="img/3.png"/></div></span>
 <span><div><img src="img/4.png"/></div></span>
 </div>
 <img src="" id="img"/>
</div>
</body>
</html>