<div class="slider">
  <div class="ul-box">
   <ul>
    <li><a href="javascript:;"><img src="img/1.jpg"/></a></li>
    <li><a href="javascript:;"><img src="img/2.jpg"/></a></li>
    <li><a href="javascript:;"><img src="img/3.jpg"/></a></li>
    <li><a href="javascript:;"><img src="img/4.jpg"/></a></li>
    <li><a href="javascript:;"><img src="img/5.jpg"/></a></li>
    <li><a href="javascript:;"><img src="img/6.jpg"/></a></li>
   </ul>
  </div>
  <div class="mask"></div>
  <div class="prev"><img src="img/btn_l.png"/></div>
  <div class="next"><img src="img/btn_r.png"/></div>
 </div>
 <script src="js/jquery-1.11.3.js"></script>
 <script src="js/slider.js"></script>
 <script>
  $('.slider').slider({
   width : 640, 
   height : 270, 
   during : 2000, //动画执行间隔
   speed : 500, //动画速度
   btnSize : 20, //底部遮罩层的按钮大小
   btnSpace : 10, //底部的按钮间隙
   direction : 1 //轮播方向默认为1，图片向左移动
  });
 </script> 

*{
 margin: 0;
 padding: 0;
 box-sizing: border-box;
}
.slider{
 position: relative;
 overflow: hidden;
}
.slider ul{
 list-style: none;
 float: left;
}
.slider ul li{
 float: left;
}
.slider .mask{
 position: absolute;
 bottom: 0;
 width: 100%;
 background-color: rgba(0, 0, 0, .3);
}
.slider .mask .sliderBtn{
 position: absolute;
 border-radius: 50%;
 background-color: #fff;
 cursor: pointer;
 background: radial-gradient(white 20%, transparent 50%);
}
.slider .prev, .slider .next{
 position: absolute;
 width: 45px; 
 height: 100%;
 background-color: rgba(0, 0, 0, .2);
 cursor: pointer;
 top: 0;
 display: none;
}
.slider .prev{
 left: 0;
}
.slider .next{
 right: 0;
}
.slider .prev img, .slider .next img{
 position: absolute;
 top: 50%;
 left: 50%;
 margin-top: -22.5px;
 margin-left: -22.5px;
} 

(function ($) {
 $.fn.slider = function (setting) { //给jQuery的实例对象绑定一个slider方法
  var defaultSetting = {
   width : 640,
   height : 270,
   during : 3000,
   speed : 500,
   btnSize : 30,
   btnSpace : 10,
   direction : 1
  }
  setting = $.extend(true, {}, defaultSetting, setting); //用传入的参数替换掉默认的设置 
  return this.each(function (i, item) { 
   var _setInterval = window.setInterval; 
   window.setInterval = function (callback, timer, param) { //重写setInterval函数，让其可以传参
    var args = Array.prototype.slice.call(arguments, 2); 
    var _fn = function () {
     callback.apply(null, args);
    }
    return _setInterval(_fn, timer);
   }

   var _this = $(this),
   ulBox = $('.ul-box', this),
   ul = $('ul', this),
   li = $('li', ul),
   img = $('img', li),
   len = li.size(),
   mask = $('.mask', this),
   index = 0,      //用来控制按钮的下标
   flag = true,      //标识动画是否执行完成
   gap,        //执行动画的按钮下标和当前按钮的下标的差
   timer;       //计时器

   _this.width(setting.width).height(setting.height);
   ulBox.width(setting.width * 3 * len).height(setting.height).css({
    marginLeft: -setting.width * len
   });
   ul.width(setting.width * len).height(setting.height);
   img.width(setting.width).height(setting.height);
   mask.height(setting.btnSize + 2 * setting.btnSpace);

   //添加btn
   for(var i = 0, str = ''; i < len; i++){
    str += '<div class="sliderBtn"></div>';
   }
   mask.html(str);
   var ulFir = ul.clone(true);
   var ulSec = ul.clone(true);
   var sliderBtn = $('.sliderBtn', '.mask');
   ulBox.append(ulFir);
   ulBox.append(ulSec);
   sliderBtn.each(function (i, item) {
    $(item).css({
     width : setting.btnSize,
     height : setting.btnSize,
     top : setting.btnSpace,
     left : parseInt(setting.width - (setting.btnSize + setting.btnSpace *2) *len, 10) /2 + setting.btnSize * i + setting.btnSpace * i * 2 + setting.btnSpace
    });
    $(item).mouseenter(function () {
     gap = Math.abs(i - index);
     i > index ? (flag && ani(1, gap)) : (flag && ani(0, gap));
    })
   });
   btnAni(0);
   //按钮样式变化
   function btnAni (index) {
    $('.sliderBtn').css('background', 'radial-gradient(white 20%, transparent 50%)');
    $('.sliderBtn').eq(index).css('background', 'radial-gradient(white 10%, transparent 30%, white 70%)');
   }
   //动画
   function ani (direction, num) {
    if(flag){
     //默认1向左运动，0向右运动
     flag = false;
     var ulfir = $('ul', ulBox).eq(0);
     var left = parseInt(ulfir.css('margin-left'), 10);
     if(direction){
      index += num;
      index = index % len;
      left = left - num * setting.width;
      ulfir.animate({
       marginLeft: left
      }, setting.speed, function () {
       if(left <= -len * setting.width){
        ulfir = ulfir.remove();  
        ulfir.css('margin-left', 0);
        ulBox.append(ulfir);
       }
       flag = true;
      });
     }else{
      index -= num;
      index = index <= -1 ? len - 1 : index;
      left = left + num * setting.width;
      ulfir.animate({
       marginLeft: left
      }, setting.speed, function () {
       if(left >= len * setting.width){
        var ulLast = $('ul', ulBox).eq(2).remove();
        ulLast.css('margin-left', 0);
        ulBox.prepend(ulLast);
        ulfir.css('margin-left', 0);
       }
       flag = true
      })
     }
     btnAni(index)
    }
   }
   //定时器
   timer = setInterval(ani, setting.during, setting.direction, 1);
   _this.hover(function () {
    $('.prev', this).css('display', 'block');
    $('.next', this).css('display', 'block');
    clearInterval(timer);

   }, function () {
    $('.prev', this).css('display', 'none');
    $('.next', this).css('display', 'none');
    timer = setInterval(ani, setting.during, setting.direction, 1);
   })
   $('.next').click(function () {
    flag && ani(1, 1);
   })
   $('.prev').click(function () {
    flag && ani(0, 1);
   })
  })
 }
})(jQuery)