原生JS實現Touch滑動反彈

<template>
    <div>
        <div class="box">
            <ul @touchstart='touchstart' @touchmove='touchmove' @touchend='touchend' class="scroll">
                <li v-for="(item, i) in list" :key="i">列表{{i}}</li>
            </ul>
        </div>
    </div>
</template>
<style>
.box{
    height: 400px;
    overflow: hidden;
    border: 2px solid #cccccc;
    width: 60px;
    text-align: center;
    position: fixed;
    left: 10px;
    top: 50%;
    transform: translateY(-50%)
}
.box ul li{
    display: flex;
    flex-direction: column;
    line-height: 30px;
}
</style>
<script>
// 參考：https://segmentfault.com/a/1190000017852497
export default {
    data () {
        return {
            list: Array(16),
            startY: 0,
            maxDown: 40, //設置最大的下滑的區間
            maxUpDown: 40,  //設置最大的上滑底下留餘的區間
            maxUpBounce: 0, //向上反彈
        }
    },
    created () {
        this.touch = {}
    },
    mounted () {
        // 求一個上滑的最大的距離
        let ulBox = document.getElementsByClassName('scroll')[0]
        let box = document.getElementsByClassName('box')[0]
        this.maxUp = - (ulBox.clientHeight - box.clientHeight + this.maxUpDown)
        // 向下反彈值
        this.maxDownBounce = - (ulBox.clientHeight - box.clientHeight)
    },
    methods: {
        touchstart (e) {
            this.touch.y1 = e.targetTouches[0].clientY
        },
        touchmove (e) {
            this.scrollH = 0
            this.touch.y2 = e.targetTouches[0].clientY
            this.scrollH = this.startY + (this.touch.y2 - this.touch.y1)
            // 限制最大的下滑空間
            if(this.scrollH > this.maxDown) {
                this.scrollH = this.maxDown
            }
            // 限制最大的上滑空間
            if(this.scrollH < this.maxUp) {
                this.scrollH = this.maxUp
            }
            scroll = document.getElementsByClassName('scroll')[0]
            scroll.style.transform = `translateY(${this.scrollH}px)` 
            scroll.style.webkitTransform = `translateY(${this.scrollH}px)`
        },
        touchend (e) {
            this.startY = this.scrollH
            // 添加反彈的動畫
            let ulBox = document.getElementsByClassName('scroll')[0]
            if(this.startY > this.maxUpBounce) {
                this.startY = this.maxUpBounce
                ulBox.style.transition = 'transform .5s'
                ulBox.style.transform = `translateY(${this.startY}px)` 
                ulBox.style.webkitTransform = `translateY(${this.startY}px)`
            }
            if(this.startY < this.maxDownBounce) {
                this.startY = this.maxDownBounce
                ulBox.style.transition = 'transform .5s'
                ulBox.style.transform = `translateY(${this.startY}px)` 
                ulBox.style.webkitTransform = `translateY(${this.startY}px)`
            }
        }

    }
}
</script>