Vue 实现返回顶部按钮，缓慢回到顶部

<template>
  <div class="scrollTop">
    <div class="backTop"
           @click="backTop">
        <button v-show="flag_scroll">
                   返回顶部
        </button>
      </div>
      //数据源
      <div></div>
    </div>
</template>    
<script>
export default {
  name: 'scrollTop',
  data() {
    return {
 
      flag_scroll: false,
      scroll: 0,
    }
  },
  computed: {},
  methods: {
  //返回顶部事件
    backTop() {
      //回到顶部方法 点击按钮调用
      let top = document.getElementsByClassName('scrollTop')[0].scrollTop
      // 实现滚动效果，缓慢回到顶部
      const timeTop = setInterval(() => {
        document.getElementsByClassName(
          'scrollTop'
        )[0].scrollTop = top -= 50

        if (top <= 0) {
          clearInterval(timeTop) //清除定时器
        }
      }, 20)
    },
   //滑动超过200时显示按钮
    handleScroll() {
      let scrollTop = document.getElementsByClassName('scrollTop')[0]
        .scrollTop
        console.log(scrollTop)
      if (scrollTop > 200) {
        this.flag_scroll = true
      } else {
        this.flag_scroll = false
      }
    },
  },
  mounted() {
    window.addEventListener('scroll', this.handleScroll, true)
  },
  destroyed() {
    window.removeEventListener('scroll', this.handleScroll, true) //移除监听事件
  },
  created() { },
}
</script>

<style scoped>
.scrollTop{
  width: 100%;
  height: 100vh;
  overflow-y: scroll;
}
.backTop {
  position: fixed;
  bottom: 50px;
  z-index: 100;
  right: 0;
  background: white;
}
</style>