js 轮播效果实例分享

<!--图片轮播   start-->
<div class="pics-ul">
  <div class="pics-ulleft">              
    <ul id="allimg">
      <li><img src="img/img01.png"/></li>  
      <li><img src="img/img2.jpg"/></li>  
      <li><img src="img/img1.jpg"/></li>  
      <li><img src="img/img3.jpg"/></li>  
      <li><img src="img/img4.jpg"/></li>  
    </ul>
    <a name="btn" id="prev" class="prev" style="display: block;"></a>
    <a name="btn" id="next" class="next" style="display: block;"></a>
     <ul id="btn" class="pagination">
     <li class="hover"><a href="#0">1</a></li>
     <li><a href="#1">2</a></li>
     <li><a href="#2">3</a></li>
     <li><a href="#3">4</a></li>
     <li><a href="#4">5</a></li>
     </ul>
     </div>
     <div class="pics-ulright"><img src="img/imgright.png"/></div>
     </div>
<!--图片轮播   end-->  

/*图片轮播*/
var but1 = document.getelementbyid("prev");
var abtn = document.getelementbyid("btn").getelementsbytagname("li"); //获取所有的按钮
var lis = document.getelementbyid('allimg').getelementsbytagname('li');
var but2 = document.getelementbyid("next");
var index = 0;
var timer = null;
but2.onclick = function() {

  index++;
  if (index > lis.length - 1) {
    index = 0;
  }
  setimg(index);

}
but1.onclick = function() {
  index--;
  if (index < 0) {
    index = lis.length - 1;
  }
  setimg(index);

}
function changeimg() {
  if (index == lis.length - 1) { //当到最后一张图片时
    index = 0
  } else {
    index++; //图片索引发生改变
  }
  setimg(index);
}
function setimg(index) {
  for (j = 0; j < lis.length; j++) {
    lis[j].style.display = "none";
  }

  lis[index].style.display = "block";
  //按钮的样式要与图片对应
  for (var i = 0; i < abtn.length; i++) {
    abtn[i].classname = ""
  }
  abtn[index].classname = "hover";
}
//自动切换
timer = setinterval(changeimg, 3000);
//按钮
for (var i = 0; i < abtn.length; i++) {
  (function() {
    var p = i
    abtn[p].onclick = function() {
      index = p;
      setimg(index);
    }

  })();
}