原生JS实现移动端Web轮播图：基于Tween算法的完整解析

<head> 
 <meta charset="UTF-8"> 
 <meta name="viewport" content="width=device-width,initial-scale=.5,maximum-scale=.5"> 
 <title>移动端轮播图</title> 
 <style> 
 * { 
 box-sizing: border-box; 
 margin: 0; 
 padding: 0 
 } 
 .banner { 
 overflow: hidden; 
 width: 100%; 
 height: 300px 
 } 
 .banner .img-wrap { 
 position: relative; 
 height: 100% 
 } 
 .banner img { 
 display: block; 
 position: absolute; 
 top: 0; 
 width: 100%; 
 height: 100% 
 } 
 </style> 
</head> 

<div class="banner"> 
 <div class="img-wrap" id="imgWrap"> 
 <img src="images/banner_3.jpg" data-index="-1"> 
 <img src="images/banner_1.jpg" data-index="0"> 
 <img src="images/banner_2.jpg" data-index="1"> 
 <img src="images/banner_3.jpg" data-index="2"> 
 <img src="images/banner_1.jpg" data-index="3"> 
 </div> 
</div> 

<script> 
 HTMLElement.prototype.tweenTranslateXAnimate = function (start, end, callback) { 
 var duration = 50; 
 var t = 0; 
 var vv = end - start; 
 var Tween = { 
 Quad: { 
 easeOut: function (t, b, c, d) { 
  return -c * (t /= d) * (t - 2) + b; 
 } 
 } 
 }; 
 
 this.timer = setInterval(function () { 
 var dis = start + Tween.Quad.easeOut(++t, 0, vv, duration); 
 this.style.transform = 'translate3d(' + dis + 'px, 0, 0)'; 
 if (vv > 0 && parseInt(this.style.transform.slice(12)) >= end) { 
 this.style.transform = 'translate3d(' + parseInt(dis) + 'px, 0, 0)'; 
 clearInterval(this.timer); 
 callback && callback(); 
 } 
 if (vv < 0 && parseInt(this.style.transform.slice(12)) <= end) { 
 this.style.transform = 'translate3d(' + parseInt(dis) + 'px, 0, 0)'; 
 clearInterval(this.timer); 
 callback && callback(); 
 } 
 }.bind(this), 4); 
 } 
</script> 

<script> 
 ~function () { 
 var lastPX = 0; // 上一次触摸的位置x坐标, 需要计算出手指每次移动的一点点距离 
 var movex = 0; // 记录手指move的x方向值 
 var imgWrap = document.getElementById('imgWrap'); 
 var startX = 0; // 开始触摸时手指所在x坐标 
 var endX = 0; // 触摸结束时手指所在的x坐标位置 
 var imgSize = imgWrap.children.length - 2; // 图片个数 
 var t1 = 0; // 记录开始触摸的时刻 
 var t2 = 0; // 记录结束触摸的时刻 
 var width = window.innerWidth; // 当前窗口宽度 
 var nodeList = document.querySelectorAll('#imgWrap img'); // 所有轮播图节点数组 NodeList 
 
 // 给图片设置合适的left值, 注意 querySelectorAll返回 NodeList, 具有 forEach方法 
 nodeList.forEach(function (node, index) { 
 node.style.left = (index - 1) * width + 'px'; 
 }); 
 
 /** 
 * 移动图片到当前的 tIndex索引所在位置 
 * @param {number} tIndex 要显示的图片的索引 
 * */ 
 function toIndex(tIndex) { 
 var dis = -(tIndex * width); 
 var start = parseInt(imgWrap.style.transform.slice(12)); 
 // 动画移动 
 imgWrap.tweenTranslateXAnimate(start, dis, function () { 
 setTimeout(function () { 
  movex = dis; 
  if (tIndex === imgSize) { 
  imgWrap.style.transform = 'translate3d(0, 0, 0)'; 
  movex = 0; 
  } 
  if (tIndex === -1) { 
  imgWrap.style.transform = 'translate3d(' + width * (1 - imgSize) + 'px, 0, 0)'; 
  movex = -width * (imgSize - 1); 
  } 
 }, 0); 
 }); 
 } 
 
 /** 
 * 处理各种触摸事件 ,包括 touchstart, touchend, touchmove, touchcancel 
 * @param {Event} evt 回调函数中系统传回的 js 事件对象 
 * */ 
 function touch(evt) { 
 var touch = evt.targetTouches[0]; 
 var tar = evt.target; 
 var index = parseInt(tar.getAttribute('data-index')); 
 if (evt.type === 'touchmove') { 
 var di = parseInt(touch.pageX - lastPX); 
 endX = touch.pageX; 
 movex += di; 
 imgWrap.style.webkitTransform = 'translate3d(' + movex + 'px, 0, 0)'; 
 lastPX = touch.pageX; 
 } 
 if (evt.type === 'touchend') { 
 var minus = endX - startX; 
 t2 = new Date().getTime() - t1; 
 if (Math.abs(minus) > 0) { // 有拖动操作 
  if (Math.abs(minus) < width * 0.4 && t2 > 500) { // 拖动距离不够,返回! 
  toIndex(index); 
  } else { // 超过一半,看方向 
  console.log(minus); 
  if (Math.abs(minus) < 20) { 
  console.log('距离很短' + minus); 
  toIndex(index); 
  return; 
  } 
  if (minus < 0) { // endX < startX,向左滑动,是下一张 
  toIndex(index + 1) 
  } else { // endX > startX ,向右滑动, 是上一张 
  toIndex(index - 1) 
  } 
  } 
 } else { //没有拖动操作 
 
 } 
 } 
 if (evt.type === 'touchstart') { 
 lastPX = touch.pageX; 
 startX = lastPX; 
 endX = startX; 
 t1 = new Date().getTime(); 
 } 
 return false; 
 } 
 
 imgWrap.addEventListener('touchstart', touch, false); 
 imgWrap.addEventListener('touchmove', touch, false); 
 imgWrap.addEventListener('touchend', touch, false); 
 imgWrap.addEventListener('touchcancel', touch, false); 
 
 }(); 
 
</script>