JavaScript实现可切换图片的幻灯片效果

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
  <meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
  <title>JS切换图片幻灯切换效果</title>
  <style>
    body, div, ul, li { margin: 0; padding: 0; }
    ul { list-style-type: none; }
    body { background: #000; text-align: center; font: 12px/20px Arial; }
    #box { position: relative; width: 322px; height: 172px; background: #fff; border-radius: 5px; border: 8px solid #fff; margin: 10px auto; }
    #box .list { position: relative; width: 320px; height: 240px; overflow: hidden; border: 1px solid #ccc; }
    #box .list li { position: absolute; top: 0; left: 0; width: 320px; height: 240px; opacity: 0; filter: alpha(opacity=0); }
    #box .list li.current { opacity: 1; filter: alpha(opacity=100); }
    #box .count { position: absolute; right: 0; bottom: 5px; }
    #box .count li { color: #fff; float: left; width: 20px; height: 20px; cursor: pointer; margin-right: 5px; overflow: hidden; background: #F90; opacity: 0.7; filter: alpha(opacity=70); border-radius: 20px; }
    #box .count li.current { color: #fff; opacity: 1; filter: alpha(opacity=100); font-weight: 700; background: #f60; }
    #tmp { width: 100px; height: 100px; background: red; position: absolute; }
  </style>
  <script type="text/javascript">
    window.onload = function() {
      var oBox = document.getElementById("box");
      var aUl = document.getElementsByTagName("ul");
      var aImg = aUl[0].getElementsByTagName("li");
      var aNum = aUl[1].getElementsByTagName("li");
      var timer = play = null;
      var i = index = 0;
      var bOrder = true;
      //切换按钮
      for(i = 0; i < aNum.length; i++) {
        aNum[i].index = i;
        aNum[i].onmouseover = function() {
          show(this.index)
        }
      }
      //鼠标划过关闭定时器
      oBox.onmouseover = function() {
        clearInterval(play)
      };
      //鼠标离开启动自动播放
      oBox.onmouseout = function() {
        autoPlay()
      };
      //自动播放函数
      function autoPlay() {
        play = setInterval(function() {
          //判断播放顺序
          bOrder ? index++ : index--;
          //正序
          index >= aImg.length && (index = aImg.length - 2, bOrder = false);
          //倒序
          index <= 0 && (index = 0, bOrder = true);
          //调用函数
          show(index)
        }, 2000);
      }
      autoPlay();//应用
      function show(a) {
        index = a;
        var alpha = 0;
        for(i = 0; i < aNum.length; i++)aNum[i].className = "";
        aNum[index].className = "current";
        clearInterval(timer);
        for(i = 0; i < aImg.length; i++) {
          aImg[i].style.opacity = 0;
          aImg[i].style.filter = "alpha(opacity=0)";
        }
        timer = setInterval(function() {
          alpha += 2;
          alpha > 100 && (alpha = 100);
          aImg[index].style.opacity = alpha / 100;
          aImg[index].style.filter = "alpha(opacity = " + alpha + ")";
          alpha == 100 && clearInterval(timer)
        }, 20);
      }
    };
  </script>
</head>
<body>
<div id="box">
  <ul class="list">
    <li class="current"><img src="img/3.jpg" width="320" height="240"/></li>
    <li><img src="img/1.jpg" width="320" height="240"/></li>
    <li><img src="img/2.jpg" width="320" height="240"/></li>
    <li><img src="img/3.jpg" width="320" height="240"/></li>
    <li><img src="img/4.jpg" width="320" height="240"/></li>
  </ul>
  <ul class="count">
    <li class="current">1</li>
    <li>2</li>
    <li>3</li>
    <li>4</li>
    <li>5</li>
  </ul>
</div>
</body>
</html>