參考：https://www.cnblogs.com/wangRong-smile/articles/11880249.html

回到頂部的DOM部分：

<div
    class="back_top"
    @mouseover="enterBackTop" // 滑鼠進入回到頂部圖示的背景顏色變深
    @mouseout="outBackTop"    // 滑鼠移開，背景顏色變淺
    ref="backTop"
    :style="{ opacity: opacity }"
    v-show="gotop"
    @click="handleScrollTop"
  >
    <span class="iconfont icon-backtotop"></span>
</div>

script部分：

props: ['ele'], // 這個是接收父元件傳遞過來的值
  data() {
    return {
      opacity: '.3',
      gotop: false,
      scrollHeight: 100,
      scrollTop: 0
    };
  },

mounted() {
    window.addEventListener('scroll', this.handleScroll, true);  // 註冊滾動事件
},

methods: {
    enterBackTop() {
      this.opacity = '1';
    },
    outBackTop() {
      
 
this.opacity = '0.3';
    },
    handleScroll(e) {
      const that = this;
      const scrollTop =
        window.pageYOffset ||
        document.documentElement.scrollTop ||
        document.body.scrollTop;
      that.scrollTop = scrollTop;
      that.scrollTop > this.scrollHeight
        ? (this
 
.gotop = true)
        : (this.gotop = false);
    },
    handleScrollTop() {
      // this.$nextTick(() => {
      //   this.ele.scrollIntoView({ behavior: 'smooth' });
      // });
      const that = this;
      const timer = setInterval(() => {
        const ispeed = Math.floor(-that.scrollTop / 5);
        document.documentElement.scrollTop = document.body.scrollTop =
          that.scrollTop + ispeed;
        if (that.scrollTop === 0) {
          clearInterval(timer);
        }
      }, 16);
    }
  }