window.onload = function ()
{
 var oBox = document.getElementById("box");
 var oList = oBox.getElementsByTagName("ul")[0];
 var aImg = oBox.getElementsByTagName("img");
 var timer = playTimer = null;
 var index = i = 0;
 var bOrder = true;
 var aTmp = [];
 
 //生成数字按钮
 for (i = 0; i < aImg.length; i++)
 {
  aTmp.push("<li>" + (i + 1) + "</li>")
 }
 
 //插入元素
 var oCount = document.createElement("ul");
 oCount.className = "count"
 oCount.innerHTML = aTmp.join("");
 oBox.appendChild(oCount);
 
 //初始化状态
 var aBtn = oBox.getElementsByTagName("ul")[1].getElementsByTagName("li");
 aBtn[index].className = "current";
 
 //按钮点击切换
 for (i = 0; i < aBtn.length; i++)
 {
  aBtn[i].index = i;
  aBtn[i].onclick = function ()
  {
   index = this.index;
   for (i = 0; i < aBtn.length; i++) aBtn[i].className = "";
   this.className = "current";   
   startMove(-(this.index * aImg[0].offsetHeight))  
  }
 }
 
 //鼠标移入展示区停止自动播放
 oBox.onmouseover = function ()
 {
  clearInterval(playTimer)
 };
 
 //鼠标离开展示区开始自动播放
 oBox.onmouseout = function ()
 {
  autoPlay()
 };
 
 //页面加载即调用自动播放
 oBox.onmouseout();
 
 //自动播放函数
 function autoPlay()
 {
  playTimer = setInterval(function ()
  {
   bOrder ? index++ : index--;   
   index == aBtn.length - 1 && (bOrder = false);
   index == 0 && (bOrder = true);
   aBtn[index].onclick();
   startMove(-(index * aImg[0].offsetHeight))
  }, 5000)
 }
 function startMove(iTarget)
 {
  clearInterval(timer);
  timer = setInterval(function ()
  {
   doMove(iTarget)
  }, 30) 
 }
 function doMove (iTarget)
 {
  var iSpeed = (iTarget - oList.offsetTop) / 10;
  iSpeed = iSpeed > 0 ? Math.ceil(iSpeed) : Math.floor(iSpeed);  
  oList.offsetTop == iTarget ? clearInterval(timer) : oList.style.top = oList.offsetTop + iSpeed + "px"
 }
};