原生JS实现简单的无缝自动轮播效果

<div id="wrap">
  <ul id="ul">
    <li>
      <img src="http://img3.imgtn.bdimg./it/u=1135520735,2369294998&fm=200&gp=0.jpg">
    </li>
    <li>
      <img src="http://img2.imgtn.bdimg./it/u=695607252,2370769232&fm=200&gp=0.jpg">
    </li>
    <li>
      <img src="http://img4.imgtn.bdimg./it/u=4133407901,1533904167&fm=200&gp=0.jpg">
    </li>
    <li>
      <img src="http://img5.imgtn.bdimg./it/u=4083237979,1376579798&fm=26&gp=0.jpg">
    </li>
    <li>
      <img src="http://img2.imgtn.bdimg./it/u=1640379911,3259036309&fm=26&gp=0.jpg">
    </li>
  </ul>
</div> 

 #wrap{
        width: 400px;
        height: 80px;
        overflow: hidden;
        margin-left: 500px;
        margin-: 300px;
        position: relative;
      }
      #ul{
        position: absolute;
        left: 0;
        : 0;
        width: 400px;
        font-size: 0;
        margin: 0;
        padding: 0;
      }

window.onload = function(){
  var odiv = document.getElementById('wrap');
  var oul = document.getElementById('ul');
  setInterval(function(){
    oul.style.left = oul.offsetLeft + 5 +'px';
  },30)

var odiv = document.getElementById('wrap');
      var oul = document.getElementById('ul');
      var oli = oul.getElementsByTagName('li');
      oul.innerHTML = oul.innerHTML + oul.innerHTML;//拼接li，因为图片可能是任意张
      oul.style.width = oli[1].offsetWidth  oli.length + 'px';//ul的宽度等于所有图片宽度的总和
    setInterval(function(){
      if (oul.offsetLeft < -oul.offsetWidth/2) {
        oul.style.left = 0;//如果ul已经显示完了一组，也就是宽度的一半，那么就把他拉回来重新轮播
      }else{
        oul.style.left = oul.offsetLeft - 2 +'px';
      }
    },30);