div class="cm-banner">
  <div class="cm-banner-list">
    <ul id="cm_banner_list">
      <!--图片宽度和高度在css中定为1920x300-->
      <li><img src="cm-banner-01.png" /></li>
      <li><img src="cm-banner-02.png" /></li>
      <li><img src="cm-banner-03.png" /></li>
      <li><img src="cm-banner-04.png" /></li>
    </ul>
    <ul class="cm-banner-num" id="cm_banner_num"></ul>
  </div>
  <div class="cm-banner-in w">
    <img src="cm-arrow-left.png" id="cm_prev" class="cm-banner-arrow" />
    <img src="cm-arrow-right.png" id="cm_next" class="cm-banner-arrow" />
  </div>
</div>

*{
  margin: 0;
  padding: 0;
}
.cm-banner {
  width: 100%;
  height: 300px;
  overflow: hidden;
  cursor: pointer;
  position: relative;
}

.cm-banner-in {
  width: 1100px;
  height: 300px;
  position: absolute;
  top: 0;
  left: 50%;
  margin-left: -550px;
}

#cm_banner_list li{
  display: none;
  position: absolute;
  top: 0;
  left: 0;
}

.cm-banner-num {
  width: 100%;
  position: absolute;
  bottom: 0;
  text-align: center;
  z-index: 2; /*如果没有在这里设置层次小圆点的点击效果无法触发*/
}

.cm-banner-num li{
  width: 10px;
  margin: 10px 3px;
  height: 10px;
  background-color: #fff;
  border-radius: 5px;
  -webkit-border-radius: 5px;
  display: inline-block;
  opacity: 0.7;
}

.cm-banner-num .active {
  background-color: #3982de;
}

.cm-banner-arrow {
  position: absolute;
  top: 50%;
  margin-top: -22px;
  opacity: 0.5;
  display: none;
}

#cm_prev {
  left: 0;
}

#cm_next {
  right: 0;
}

$(function(){
  //鼠标移入显示箭头按钮
  $('.cm-banner').hover(function(){
    $('.cm-banner-arrow').show();
    clearInterval(cm_timer);
  },function(){
    $('.cm-banner-arrow').hide();
    cm_timer = setInterval(function(){
      i++;
      if(i > cm_length - 1){
        i = 0;
      }
      $('#cm_banner_list li').eq(i).fadeIn(800).siblings().fadeOut(800);
      cm_toggle(i);
    },2500);
  });

  //鼠标移入箭头按钮高亮
  $('.cm-banner-arrow').hover(function(){
    $(this).css('opacity','1');
  },function(){
    $(this).css('opacity','0.5');
  });

  //初始化必要变量
  var i = 0;
  var cm_length = $('#cm_banner_list li').length;
  var cm_toggle = function(point){
    $('#cm_banner_num li').eq(point).addClass('active').siblings().removeClass('active');
  };

  //动态添加小圆点
  for(j = 0;j < cm_length;j++){
    $('#cm_banner_num').append('<li></li>');
  }

  //给第一个小圆点添加样式
  $('#cm_banner_num li').first().addClass('active');

  //给第一张图片添加样式
  $('#cm_banner_list li').first().css('display','block');

  //鼠标点击左箭头切换
  $('#cm_prev').click(function(){
    i--;
    if(i < 0){
      i = cm_length - 1;
    }
    $('#cm_banner_list li').eq(i).fadeIn(800).siblings().fadeOut(800);
    cm_toggle(i);
  });

  //鼠标点击右箭头切换
  $('#cm_next').click(function(){
    i++;
    if(i > cm_length - 1){
      i = 0;
    }
    $('#cm_banner_list li').eq(i).fadeIn(800).siblings().fadeOut(800);
    cm_toggle(i);
  });

  //鼠标点击圆点切换
  $('#cm_banner_num li').click(function(){
    var cm_index = $(this).index();
    $('#cm_banner_list li').eq(cm_index).fadeIn(800).siblings().fadeOut(800);
    i = cm_index;
    cm_toggle(cm_index);
  });

  //自动播放
  cm_timer = setInterval(function(){
    i++;
    if(i > cm_length - 1){
      i = 0;
    }
    $('#cm_banner_list li').eq(i).fadeIn(800).siblings().fadeOut(800);
    cm_toggle(i);
  },2500);
});