JavaScript实现简易图片轮播功能

<div id="head"> 
<button id="prev" onmousedown="p()" onmouseout="cal()"><</button>
<img height="500px" width="500px" src="image/dell.jpg" alt="Dell">
<button id="next" onmousedown="n()" onmouseout="cal()">></button>
</div>

<style type="text/css">

*
{
 margin: 0;
 padding: 0;
}

#head
{
 width:800px;
 height:500px;
 border-radius: 5px;
 border: 2px solid pink;
 margin: 200px auto;
 text-align: center; 
}

#prev
{
 width: 30px;
 height: 30px;
 border: 0px;
 border-radius: 5px;
 background-color:white;
 color: black;
 position: relative;
 margin-top: 250px;
 float: left; 
}

#next
{
 width: 30px;
 height: 30px;
 border: 0px;
 border-radius: 5px;
 background-color:white;
 color: black;
 position: relative;
 margin-top: 250px;
 float: right; 
}

</style>

<script>

 var prev=document.getElementById("prev");
 var next=document.getElementById("next");
 var img=document.getElementsByTagName("img")[0];
 var imgArr=["image/dell.jpg/dell.jpg","image/dell.jpg/sony.jpg","image/dell.jpg/费列罗.jpg","image/dell.jpg/Nike.jpg"];
 var index=0;
 
 //点击左箭头，切换上一张
 function p(){

 if(index==0)
 {
 index=imgArr.length;
 }

 index--;

 img.src=imgArr[index];

 }
 //点击右箭头，切换下一张
 function n(){

 if(index==imgArr.length)
 {
 index=0;
 }

 img.src=imgArr[index];

 index++;

 }
 //设置自动播放
 time=setInterval("p()",2000);
 
 //鼠标移入箭头内，停止自动播放
 function cal(){
 clearInterval(time);
 }

</script>