作者：前端精髓
https://blog.csdn.net/wu_xianqiang/article/details/136777572
在移动端，如果你使用过 overflow: scroll 生成一个滚动容器，会发现它的滚动是比较卡顿，呆滞的。为什么会出现这种情况呢？
因为我们早已习惯了目前的主流操作系统和浏览器视窗的滚动体验，比如滚动到边缘会有回弹，手指停止滑动以后还会按惯性继续滚动一会，手指快速滑动时页面也会快速滚动。而这种原生滚动容器却没有，就会让人感到卡顿。
首先，让我们来看一下它是怎样让滚动更流畅的吧。
<html><head><meta charset="UTF-8" /><meta name="viewport" content="width=device-width, initial-scale=1.0" /><title>Document</title></head><body><div id="app"></div><template id="tpl"><divclass="wrapper"ref="wrapper"@touchstart.prevent="onStart"@touchmove.prevent="onMove"@touchend.prevent="onEnd"@touchcancel.prevent="onEnd"@mousedown.prevent="onStart"@mousemove.prevent="onMove"@mouseup.prevent="onEnd"@mousecancel.prevent="onEnd"@mouseleave.prevent="onEnd"@transitionend="onTransitionEnd"><ul class="list" ref="scroller" :style="scrollerStyle"><li class="list-item" v-for="item in list">{{item}}</li></ul></div></template><style>body,ul {margin: 0;padding: 0;}ul {list-style: none;}.wrapper {width: 100vw;height: 100vh;overflow: hidden;}.list {background-color: #70f3b7;}.list-item {height: 40px;line-height: 40px;width: 100%;text-align: center;border-bottom: 1px solid #ccc;}</style><script src="https://cdn.jsdelivr.net/npm/vue@2"></script><script>new Vue({el: "#app",template: "#tpl",computed: {list() {let list = [];for (let i = 0; i < 100; i++) {list.push(i);}return list;},scrollerStyle() {return {transform: `translate3d(0, ${this.offsetY}px, 0)`,"transition-duration": `${this.duration}ms`,"transition-timing-function": this.bezier,};},},data() {return {minY: 0,maxY: 0,wrapperHeight: 0,duration: 0,bezier: "linear",pointY: 0, // touchStart 手势 y 坐标startY: 0, // touchStart 元素 y 偏移值offsetY: 0, // 元素实时 y 偏移值startTime: 0, // 惯性滑动范围内的 startTimemomentumStartY: 0, // 惯性滑动范围内的 startYmomentumTimeThreshold: 300, // 惯性滑动的启动 时间阈值momentumYThreshold: 15, // 惯性滑动的启动 距离阈值isStarted: false, // start锁};},mounted() {this.$nextTick(() => {this.wrapperHeight =this.$refs.wrapper.getBoundingClientRect().height;this.minY =this.wrapperHeight -this.$refs.scroller.getBoundingClientRect().height;});},methods: {onStart(e) {const point = e.touches ? e.touches[0] : e;this.isStarted = true;this.duration = 0;this.stop();this.pointY = point.pageY;this.momentumStartY = this.startY = this.offsetY;this.startTime = new Date().getTime();},onMove(e) {if (!this.isStarted) return;const point = e.touches ? e.touches[0] : e;const deltaY = point.pageY - this.pointY;this.offsetY = Math.round(this.startY + deltaY);const now = new Date().getTime();// 记录在触发惯性滑动条件下的偏移值和时间if (now - this.startTime > this.momentumTimeThreshold) {this.momentumStartY = this.offsetY;this.startTime = now;}},onEnd(e) {if (!this.isStarted) return;this.isStarted = false;if (this.isNeedReset()) return;const absDeltaY = Math.abs(this.offsetY - this.momentumStartY);const duration = new Date().getTime() - this.startTime;// 启动惯性滑动if (duration < this.momentumTimeThreshold &&absDeltaY > this.momentumYThreshold) {const momentum = this.momentum(this.offsetY,this.momentumStartY,duration);this.offsetY = Math.round(momentum.destination);this.duration = momentum.duration;this.bezier = momentum.bezier;}},onTransitionEnd() {this.isNeedReset();},momentum(current, start, duration) {const durationMap = {noBounce: 2500,weekBounce: 800,strongBounce: 400,};const bezierMap = {noBounce: "cubic-bezier(.17, .89, .45, 1)",weekBounce: "cubic-bezier(.25, .46, .45, .94)",strongBounce: "cubic-bezier(.25, .46, .45, .94)",};let type = "noBounce";// 惯性滑动加速度const deceleration = 0.003;// 回弹阻力const bounceRate = 10;// 强弱回弹的分割值const bounceThreshold = 300;// 回弹的最大限度const maxOverflowY = this.wrapperHeight / 6;let overflowY;const distance = current - start;const speed = (2 * Math.abs(distance)) / duration;let destination =current + (speed / deceleration) * (distance < 0 ? -1 : 1);if (destination < this.minY) {overflowY = this.minY - destination;type =overflowY > bounceThreshold ? "strongBounce" : "weekBounce";destination = Math.max(this.minY - maxOverflowY,this.minY - overflowY / bounceRate);} else if (destination > this.maxY) {overflowY = destination - this.maxY;type =overflowY > bounceThreshold ? "strongBounce" : "weekBounce";destination = Math.min(this.maxY + maxOverflowY,this.maxY + overflowY / bounceRate);}return {destination,duration: durationMap[type],bezier: bezierMap[type],};},// 超出边界时需要重置位置isNeedReset() {let offsetY;if (this.offsetY < this.minY) {offsetY = this.minY;} else if (this.offsetY > this.maxY) {offsetY = this.maxY;}if (typeof offsetY !== "undefined") {this.offsetY = offsetY;this.duration = 500;this.bezier = "cubic-bezier(.165, .84, .44, 1)";return true;}return false;},// 停止滚动stop() {const matrix = window.getComputedStyle(this.$refs.scroller).getPropertyValue("transform");this.offsetY = Math.round(+matrix.split(")")[0].split(", ")[5]);},},});</script></body></html>
可以发现，在增加惯性滚动，边缘回弹等效果之后，明显流畅、舒服了很多。那么，这些效果是怎么实现的呢？在用户滑动操作结束时，还会继续惯性滚动一段。首先看一下源码中的函数，这是 touchend 事件的处理函数，也就是用户滚动操作结束时的逻辑。