JS实现焦点图轮播

<!DOCTYPE html>
<html>
 <head> 
  <meta charset="UTF-8" /> 
  <title>JS实现焦点图轮播效果</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 len = 5;
var animated = false;
var interval = 3000;
var timer;
function animate(offset) {
    if(offset == 0) {
        return;
    }
    animated = true;
    var time = 300;
    var inteval = 10;
    var speed = offset / (time / inteval);
    var left = parseInt(list.style.left) + offset;
    var go = function() {
        if((speed > 0 && parseInt(list.style.left) < left) ||
         (speed < 0 && parseInt(list.style.left) > left)) {
            list.style.left = parseInt(list.style.left) + speed + 'px';
            setTimeout(go, inteval);
        } else {
            list.style.left = left + 'px';
            if(left > -200) {
                list.style.left = -600 * len + 'px';
            }
            if(left < (-600 * len)) {
                list.style.left = '-600px';
            }
            animated = false;
        }
    }
    go();
} 
function showButton() {
    for(var i = 0; i < buttons.length; i++) {
        if(buttons[i].className == 'on') {
            buttons[i].className = '';
            break;
        }
    }
    buttons[index - 1].className = 'on';
}
function play() {
    timer = setTimeout(function() {
        next.onclick();
        play();
    }, interval);
}
function stop() {
    clearTimeout(timer);
} 
next.onclick = function() {
    if(animated) {
        return;
    }
    if(index == 5) {
        index = 1;
    } else {
        index += 1;
    }
    animate(-600);
    showButton();
}
prev.onclick = function() {
    if(animated) {
        return;
    }
    if(index == 1) {
        index = 5;
    } else {
        index -= 1;
    }
    animate(600);
    showButton();
}
for(var i = 0; i < buttons.length; i++) {
    buttons[i].onclick = function() {
        if(animated) {
            return;
        }
        if(this.className == 'on') {
            return;
        }
        var myIndex = parseInt(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;"> 
    <!-- 放最后的一张图片 -图片需要改为自己的图片路径 --> 
    <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" /> 
    <!-- 放第一张的图片 --> 
    <img src="img/1.jpg" alt="5" /> 
   </div> 
   <div id="buttons"> 
    <span index="1" class="on"></span> 
    <span index="2"></span> 
    <span index="3"></span> 
    <span index="4"></span> 
    <span index="5"></span> 
   </div> 
   <a href="javascript:;" id="prev" class="arrow">&lt;</a> 
   <a href="javascript:;" id="next" class="arrow">&gt;</a> 
  </div>  
 </body>
</html>