单独点击圆点按钮和左右按钮不会出问题，先点圆点按钮再点左右按钮就会出问题？
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>焦点轮播图</title>
<style type="text/css">
*{ margin: 0; padding: 0; text-decoration: none;}
body { padding: 20px;}
#container { width: 600px; height: 400px; border: 3px solid #333; overflow: hidden; position: relative;}
#list { width: 4200px; height: 400px; position: absolute; z-index: 1;}
#list img { float: left;}
#buttons { position: absolute; height: 10px; width: 100px; z-index: 2; bottom: 20px; left: 250px;}
#buttons span { cursor: pointer; float: left; border: 1px solid #fff; width: 10px; height: 10px; border-radius: 50%; background: #333; margin-right: 5px;}
#buttons .on { background: orangered;}
.arrow { cursor: pointer; display: none; line-height: 39px; text-align: center; font-size: 36px; font-weight: bold; width: 40px; height: 40px; position: absolute; z-index: 2; top: 180px; background-color: RGBA(0,0,0,.3); color: #fff;}
.arrow:hover { background-color: RGBA(0,0,0,.7);}
#container:hover .arrow { display: block;}
#prev { left: 20px;}
#next { right: 20px;}
</style>
<script type="text/javascript">
window.onload=function(){
var container=document.getElementById('container');
var list=document.getElementById('list');
var buttons=document.getElementById('buttons').getElementsByTagName('span');
var prev=document.getElementById('prev');
var next=document.getElementById('next');
var index=1;
var animated=false;
var timer;
function animate(offset){
if(offset==0){
return;
}
animated=true;
var newLeft=parseInt(list.style.left)+offset;
var time=300;//位移总时间
var interval=10;//位移间隔时间
var speed=offset/(time/interval);//位移距离/位移次数
function go(){
if((speed<0&&parseInt(list.style.left)>newLeft)||(speed>0&&parseInt(list.style.left)<newLeft)){
list.style.left=parseInt(list.style.left)+speed+'px';
setTimeout(go,interval);
}else{
animated=false;
list.style.left=newLeft+'px';
if(newLeft>-600){
list.style.left=-3000+'px';
}
if(newLeft<-3000){
list.style.left=-600+'px';
}
}
}
go();
}
function play(){
timer=setInterval(function(){
next.onclick();
},3000);
}
function stop(){
clearInterval(timer);
}
function showButton(){
for (var i = 0; i < buttons.length; i++) {
if(buttons[i].className=='on'){
buttons[i].className='';
break;
}
}
buttons[index - 1].className = 'on';
}
next.onclick=function(){
if(index==5){
index=1;
}else{
index+=1;
}
if(!animated){
animate(-600);
}
showButton();
}
prev.onclick=function(){
if(index==1){
index=5;
}else{
index-=1;
}
showButton();
if(!animated){
animate(600);
}
}
for (var i = 0; i < buttons.length; i++) {
buttons[i].onclick=function(){
if(this.className=='on'){
return;
}
var myIndex=this.getAttribute('index');
var offset=-600*(myIndex-index);
animate(offset);
index=myIndex;
showButton();
}
}
container.onmouseover=stop;
container.onmouseout=play;
play();
}
</script>
</head>
<body>
<div id="container">
<div id="list" style="left: -600px;">
<img src="img/5.jpg" alt="1"/>
<img src="img/1.jpg" alt="1"/>
<img src="img/2.jpg" alt="2"/>
<img src="img/3.jpg" alt="3"/>
<img src="img/4.jpg" alt="4"/>
<img src="img/5.jpg" alt="5"/>
<img src="img/1.jpg" alt="5"/>
</div>
<div id="buttons">
<span index="1"></span>
<span index="2"></span>
<span index="3"></span>
<span index="4"></span>
<span index="5"></span>
</div>
<a href="javascript:;" id="prev"><</a>
<a href="javascript:;" id="next">></a>
</div>
</body>
</html>
