<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>任务一</title>
<style>
*{
margin: 0;
padding: 0;
}
#outer{
width: 500px;
margin: 50px auto;
padding: 10px;
text-align: center;
}
</style>
<script type="text/javascript">
window.onload=function(){
var prev=document.getElementById("prev");
var next=document.getElementById("next");
var img=document.getElementsByTagName("img")[0];
var imgArr=["images/1.jpg ", "images/2.gif","images/2.jpg"];
var index=0;
var info=document.getElementById("info");
info.innerHTML="一共"+imgArr.length+"张图片，这是第"+(index+1)+"张";
prev.onclick=function(){
//alert("上一张");
index--;
if(index<0){
index=imgArr.length-1;
}
img.src=imgArr[index];
info.innerHTML="一共"+imgArr.length+"张图片，当前第"+(index+1)+"张";
};
next.onclick=function(){
//alert("上一张");
index++;
if(index>imgArr.length-1){
index=0;
}
img.src=imgArr[index];
info.innerHTML="一共"+imgArr.length+"张图片，当前第"+(index+1)+"张";
};
};
</script>
</head>
<body>
<div id="outer">
<p id="info">一共有3张，这是第一张</p>
<img src="images/1.jpg"/>
<button id="prve">上一张</button>
<button id="next">下一张</button>
</div>
</body>
</html>
```
