JS实现动态无缝轮播

<div class="banner" id="banner">
    <ul class="clear" >
      <li style="left:0" ><img src="k1.jpg"></li>
      <li style="left:100%" ><img src="k-2.jpg"></li>
      <li style="left:100%"><img src="k-3.jpg"></li>
    </ul>
    <div class="pageNav"></div>
    <div class="leftBtn"></div>
    <div class="rightBtn"></div>
</div>

.clear:after{
     display:block;
     content:"";
     clear:both;
    }
    .banner{
      width: 100%;
      position:relative;
      height: 390px;
    }
    .banner ul{
      width: 100%;
      height: 390px;
      list-style-type:none;
      overflow: hidden;
    }
    .banner ul li{
      width: 100%;
      position: absolute;
    }
    .pageNav{
      position: absolute;
      left:50%;
      bottom:20px;
      transform: translateX(-50%);
    }
    .pageNav a{
      display:inline-block;
      margin:0 5px;
      width: 20px;
      height: 20px;
      background-color:#fff;
      border-radius:50%;
      border:2px solid #000;
      cursor:pointer;
    }
    .pageNav a.cur{
      background-color:red;
    }
    .leftBtn, .rightBtn{
      position:absolute;
      top: 50%;
      transform:translateY(-50%);
      width: 40px;
      height: 50px;
      background-color:rgba(0, 0, 0, 0.5);
      cursor:pointer;
    }
    .leftBtn{
      left:0;
    }
    .rightBtn{
      right:0;
    }
    .leftBtn:hover,.rightBtn:hover{
      background-color:rgba(0, 0, 0, 0.8);
 }

var banner=document.getElementById("banner");
  var ul=banner.getElementsByTagName("ul")[0];
  var li=ul.getElementsByTagName("li");
  var pageNav=banner.getElementsByClassName("pageNav")[0],leftBtn=document.getElementsByClassName("leftBtn")[0],rightBtn=document.getElementsByClassName("rightBtn")[0],n=0,index=0,timerElem=null,state=false;
  for(var i=0;i<li.length;i++){//给图片底下添加按钮
    pageA=document.createElement("a");
    if(i==0){
      pageA.className="cur";
    }
    pageNav.appendChild(pageA);
  }
  pageNav.addEventListener('click',pageNavClick,false);
  function pageNavClick(e){
    if(state){
      return;
    }
    e=e||window.event;//兼容性考虑
    for(var i=0;i<li.length;i++){
      if(pageNav.children[i]==e.target){
        index=n;
        var offset=i-n;
        n=i;
        showBtn(n);
        if(offset>0){
          showImg(-100);
        }else{
          showImg(100);
        }
      }
    }
  }
  function showBtn(index){
    for(var z=0;z<li.length;z++){
      pageNav.children[z].className="";
    }
    pageNav.children[index].className="cur";
  }
  function showImg(offset){
    clearInterval(timerElem);
    var speed=offset/20;
    timerElem=setInterval(function(){
      state=true;
      if(parseInt(li[n].style.left)==0){
        state=false;
        clearInterval(timerElem);
        li[n].style.left="0";
        for(var l=0;l<n;l++){
          li[l].style.left="-100%"
        }
        for(var r=n+1;r<li.length;r++){
          li[r].style.left="100%";
        }
      }else{
        li[n].style.left=parseInt(li[n].style.left)+speed+"%";
        li[index].style.left=parseInt(li[index].style.left)+speed+"%";
      }
    },100)
  }
  leftBtn.onclick=function(){
    if(state){
      return;
    }
    index=n;
    n--;
    if(n<0){
      n=li.length-1;
      li[n].style.left="-100%";
    }
    showBtn(n);
    showImg(100);
  }
  rightBtn.onclick=function(){
    if(state){
      return;
    }
    index=n;
    n++;
    if(n>li.length-
      1){
      n=0;
      li[n].style.left="100%";
    }
    showBtn(n);
    showImg(-100);
  }
  var timer;
  timer=setInterval(autoLunbo,3000);
  function autoLunbo(){
    rightBtn.onclick();
  }
  banner.onmouseover=function(){
    clearInterval(timer);
  }
  banner.onmouseout=function(){
    timer=setInterval(autoLunbo,3000);
}