jsはシームレスな輪播図の特効を実現します。

var config = {
 imgWidth:380,//    
 dotWidth:8,//     
 doms:{
 divImgs:document.querySelector('.imgs'),
 divDots:document.querySelector('.circle'),
 divDirection:document.querySelector('.direction'),
 divContainer:document.querySelector('.container')
 },
 curIndex:0,//      ，0 ~ imgNumber-1
 timer:{
 duration:16,//      
 total:1000,//   
 id:null//     
 }
}
//     
config.imgNumber = config.doms.divImgs.children.length;
//       
config.imgsWidth = (config.imgNumber + 2)*config.imgWidth;
config.dotsWidth = (config.imgNumber + 2)*config.dotWidth;

//   
function inti(){
 intiWidth();
 intiCount();
 intiElement();
 intiPosition();
 function intiWidth(){
 config.doms.divImgs.style.width = config.imgsWidth + 'px';
 config.doms.divDots.style.width = config.dotsWidth + 'px';
 }
 function intiCount(){
 for(var i = 0; i < config.imgNumber; i ++){
 var p = document.createElement('p');
 config.doms.divDots.appendChild(p);
 }
 }
 function intiElement(){
 var first = config.doms.divImgs.children[0],last = config.doms.divImgs.children[config.imgNumber-1];
 var newImg = first.cloneNode(true);//    
 config.doms.divImgs.appendChild(newImg);
 newImg = last.cloneNode(true);
 config.doms.divImgs.insertBefore(newImg,first);
 }
 function intiPosition(){
 var left = (-config.curIndex-1)*config.imgWidth;
 config.doms.divImgs.style.marginLeft = left + 'px';
 setDots();//            
 }
}
inti();

//            
function setDots(){
 for(var i = 0; i < config.doms.divDots.children.length; i++){
 var dot = config.doms.divDots.children[i];
 if(i === config.curIndex){
 dot.className = 'select';
 }else{
 dot.className = '';
 }
 }
}

/*
     
 index:     
 directions:       （left,right）
*/
function switchTo(index,directions){
 if(index === config.curIndex){
 return;
 }
 if(!directions){
 directions = 'right';//           
 }

 //       ;      marginLeft
 var newLeft = (-index-1)*config.imgWidth;
 animateSwitch();
 //config.doms.divImgs.style.marginLeft = newLeft + 'px';
 
 //            
 config.curIndex = index;
 setDots();

 //          
 var number = Math.ceil(config.timer.total/config.timer.duration);
 //      
 var curNumber = 0;
 
 var distance,//     
 totalWidth = config.imgNumber*config.imgWidth,
 marginLeft = parseFloat(getComputedStyle(config.doms.divImgs).marginLeft);
 if(directions === 'left'){
 if(newLeft < marginLeft){
 distance = newLeft - marginLeft;
 }else{
 distance = -(totalWidth-Math.abs(newLeft - marginLeft));
 }
 }
 if(directions === 'right'){
 if(newLeft > marginLeft){
 distance = newLeft - marginLeft;
 }else{
 distance = totalWidth-Math.abs(newLeft - marginLeft);
 }
 } 

 //       
 var everDistence = distance/number; 

 //    marginLeft
 function animateSwitch(){
 clearAnimate();
 config.timer.id = setInterval(function(){

 marginLeft += everDistence;
 if(directions === 'left' && Math.abs(marginLeft) > totalWidth){
 marginLeft += totalWidth;
 }
 else if(directions === 'right' && Math.abs(marginLeft) < config.imgWidth){
 marginLeft -= totalWidth;
 }
 config.doms.divImgs.style.marginLeft = marginLeft + 'px';

 curNumber ++;
 if(curNumber === number){
 clearAnimate();
 }
 },config.timer.duration);
 }

 //     
 function clearAnimate(){
 clearInterval(config.timer.id);
 config.timer.id = null;
 }
}

//             
var timer = setInterval(function(){
 toRight();
},2000);
config.doms.divContainer.onmouseleave = function() {
 timer = setInterval(function(){
 toRight();
 },2000);
}
//          
config.doms.divContainer.onmouseover = function() {
 clearInterval(timer);
}

//      
config.doms.divDirection.onclick = function(e){
 clearInterval(timer);
 if(e.target.classList.contains('left')){
 toLeft();
 }
 if(e.target.classList.contains('right')){
 toRight();
 }
}

function toLeft(){
 var index = config.curIndex - 1;
 if(index < 0){
 index = config.imgNumber - 1;
 }
 switchTo(index,'right');
}
function toRight(){
 var index = config.curIndex + 1;
 if(index > config.imgNumber - 1){
 index = 0;
 }
 switchTo(index,'left');
}

//       
config.doms.divDots.onclick = function(e){
 if(e.target.tagName === 'P'){
 var index = Array.from(this.children).indexOf(e.target);
 switchTo(index,index > config.curIndex? 'left' : 'right')
 }
}

<!DOCTYPE html>
<html lang="en">
<head>
 <meta charset="UTF-8">
 <title>     </title>
 <link rel="stylesheet" href="index.css" rel="external nofollow" >
</head>
<body>
 <div class="container">
 <div class="imgs">
 <img class="item" src="../imagejpg/1.jpg" alt="">
 <img class="item" src="../imagejpg/2.jpg" alt="">
 <img class="item" src="../imagejpg/3.jpg" alt="">
 </div>
 <div class="circle">
 <!-- <p></p>
 <p class="select"></p>
 <p></p>
 <p></p>
 <p></p> -->
 </div>
 <div class="direction">
 <div class="item left">&lt;</div>
 <div class="item right">&gt;</div>
 </div>
 </div>
 <script src="./index.js">
 
 </script>
</body>
</html>

.container{
 width:380px;
 height:250px;
 border:1px solid;
 margin:0 auto;
 position:relative;
 overflow: hidden;
}
.container .imgs{
 
}
.container .imgs .item{
 width:380px;
 height:250px;
 display:block;
 float:left;
 top:0;
}
.container .circle{
 position:absolute;
 left:0;
 right:0;
 margin:0 auto;
 background:rgba(0,0,0,.3);
 bottom:8px;
 border-radius:5px;
}
.container .circle p{
 width:8px;
 height:8px;
 background:#fff;
 border-radius:50%;
 float:left;
 margin:2px;
 cursor:pointer;
}
.container .circle p.select{
 background:#f40;
}
.container .direction .item{
 background:rgba(0,0,0,.4);
 position:absolute;
 top:120px;
 width:20px;
 height:26px;
 padding:2px;
 box-sizing:border-box;
 display:none;
 cursor:pointer;
}
.container .direction .item:hover{
 background:rgba(0,0,0,.5);
}
.container:hover .direction .item{
 display:block;
}
.container .direction .left{
 left:0;
 border-radius:0 15px 15px 0;
}
.container .direction .right{
 right:0;
 padding-left:6px;
 border-radius:15px 0 0 15px;
}