JavaScript实现无缝无限轮播的原理与代码

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <title>无限轮播</title>
  <style>
    * {
      margin: 0;
      padding: 0;
      list-style: none;
    }
    img {
      vertical-align: top;
    }
    #slider {
      width: 520px;
      height: 280px;
      border: 1px solid #000;
      padding: 10px;
      margin: 100px auto;
      position: relative;

    }
    #top {
      width: 100%;
      height: 100%;
      position: relative;
      overflow: hidden;
    }
    #top ul {
      width: 3120px;
      height: 100%;
      position: absolute;
      left: 0;
      top: 0;
    }
    #top ul li {
      width: 520px;
      height: 280px;
      float: left;
    }
    #slider ol {
      position: absolute;
      right: 10px;
      bottom: 10px;
    }
    #slider ol li {
      width: 20px;
      height: 20px;
      background-color: darkgrey;
      display: inline-block;
      border-radius: 50%;
      margin-right: 3px;
      cursor: pointer;
    }
    #slider ol li.current {
      background-color: orangered;
    }
  </style>
</head>
<body>
  <div id="slider">
    <div id="top">
      <ul id="ul">
        <li><img src="images/pic01.jpg" alt=""></li>
        <li><img src="images/pic02.jpg" alt=""></li>
        <li><img src="images/pic03.jpg" alt=""></li>
        <li><img src="images/pic04.jpg" alt=""></li>
        <li><img src="images/pic05.jpg" alt=""></li>
      </ul>
    </div>
    <ol id="ol">
    </ol>
  </div>
<script src="js/myFunc.js"></script>
<script>
  window.onload = function () {
    // 1.获取需要的标签
    var lis = $("ul").children;

    // 6.自动轮播参数定义（图片索引，圆点索引）
    var currentIndex = 0, indicatorIndex = 0;

    // 2.克隆li标签(将第一个li标签克隆一份到最后一个li标签后面)
    $("ul").appendChild(lis[0].cloneNode(true));

    // 3.动态创建右下角的圆点
    for(var i=0; i<lis.length-1; i++){ // 因为克隆了一个li，所以需要减1
      var li = document.createElement("li");
      $("ol").appendChild(li);
    }

    // 4.第一个圆点选中
    $("ol").children[0].className = "current";

    // 5.监听鼠标进入圆点
    var olLis = $("ol").children;
    for(var j=0; j<olLis.length; j++){
      (function (j) { // 闭包
        // 5.1 获取单独的li标签
        var li = olLis[j];

        // 5.2 鼠标进入
        li.onmouseover = function () {
          for(var i=0; i<olLis.length; i++){ // 排他思想
            olLis[i].className = "";
          }

          this.className = "current";

          // 5.3 轮播图动起来
          constant($("ul"), -(520 * j), 60);

          // 6.1
          currentIndex = indicatorIndex = j;
        }
      })(j)
    }

    // 7.自动轮播
    var timer = setInterval(autoPlay, 1000);

    // 8.清除和设置定时器
    $("slider").onmouseover = function () {
      clearInterval(timer);
    };

    $("slider").onmouseout = function () {
      timer = setInterval(autoPlay, 1000);
    };

    /**
     * 自动轮播函数
     */
    function autoPlay() {
      // 7.1 ul 滚动起来
      currentIndex++;
      if(currentIndex > lis.length-1){
        $("ul").style.left = 0;
        currentIndex = 1;
      }
      constant($("ul"), -currentIndex * 520, 60);

      // 7.2 圆点滚动起来
      indicatorIndex++;
      if(indicatorIndex > olLis.length-1){
        indicatorIndex = 0;
      }
      for(var i=0; i<olLis.length; i++){ // 排他思想
        olLis[i].className = "";
      }

      olLis[indicatorIndex].className = "current";
    }
  }
</script>
</body>
</html>