javascript - 轮播图显示不了图片-PHP中文网问答

    <!doctype html>
<html lang="zh-cn">
<head>
    <meta charset="utf-8">
    <title>图片轮播</title>
    <style type="text/css">
    body{
      font:12px "微软雅黑";
    }
    body, p, ul, li {
  margin: 0;
  padding: 0;
}
    img{
        width:600px;
        height:300px;
        position:absolute;
        left:100px;
    }
    p{
        width:800px;
        height:500px;
        margin:0 auto;
        position:relative;
    }
    ul{
         position:absolute;
         right:400px;
         top:250px;
         z-index:5px;
          overflow:hidden;

    }
    li{
        width:50px;
        height:50px;
        display:inline;
       cursor:pointer;
        background:#0003FF;
       border-radius:50%;
        color:white;
        opacity: 0.7;
        margin-left:20px;
    }
    </style>
</head>
<body>


<p>
    <img src="http://1.yuhuo.sinaapp.com/3.jpg" >
    <ul>
        <li>1</li>
        <li>2</li>
        <li>3</li>
    </ul>
</p>


</body>


<

script type="text/javascript">
   var imgs=document.getElementsByTagName("img")[0];
  var imgSrc=new Array("http://1.yuhuo.sinaapp.com/3.jpg","http://1.yuhuo.sinaapp.com/2.jpg","http://1.yuhuo.sinaapp.com/1.jpg");
  var lis=document.getElementsByTagName("li");
  for(var i=0;i<lis.length;i++){
    lis[0].onclick=function(){
     imgs.setAttribute("src",imgSrc[i]);

    }
  }

</script>
</html>

为什么这样写不行呢，点击显示不了图片？

javascript<script src="jquery-1.9.1.min.js"></script> <script type="text/javascript"> var imgSrc = new Array("http://1.yuhuo.sinaapp.com/3.jpg", "http://1.yuhuo.sinaapp.com/2.jpg", "http://1.yuhuo.sinaapp.com/1.jpg"); $(function(){ $( "ul li" ).each(function(i, e) { $(this).click(function(){ $("#img").attr("src", imgSrc[i]) }); }); }); </script>

<script type="text/javascript"> var imgs=document.getElementsByTagName("img")[0]; var imgSrc=new Array("http://1.yuhuo.sinaapp.com/3.jpg","http://1.yuhuo.sinaapp.com/2.jpg","http://1.yuhuo.sinaapp.com/1.jpg"); var lis=document.getElementsByTagName("li"); for(var i=0;i<lis.length;i++){ lis[i].num = i; lis[i].onclick=function(){ imgs.setAttribute("src",imgSrc[this.num]); } } </script>