vue 监听列表元素滚动到页面可视区

 

下面看代码吧

<template>
  <div>
    <ul class="ulBox" id="ulBox">
      <li class="li" :id="'id'+item" v-for="(item,index) in list" :key="index">
        {{item}}
      </li>
    </ul>
  </div>
</template>

<script>
  export default {
  data() {
    return {
      list: [1,2,3,4,5,6,7,8,9],
    };
  },
  created() {
  },
  mounted() {
    window.addEventListener('scroll', this.scrollToTop);
  },
  methods: {
    scrollToTop() {
      // 获取视窗高度
      var domHight = document.body.offsetHeight;
      // dom滚动位置
      var scrollTop = window.pageYOffset || document.documentElement.scrollTop || document.body.scrollTop;
      // 获取监听元素
      var id;
      // 获取监听元素本身高度
      var scrollHeight;
      // 获取监听元素距离视窗顶部距离
      var offsetTop;
      // 获取监听元素距离顶部高度-窗口高度 
      var top;
      // 元素距离底部的高度+元素本身高度
      var bottom;
      this.list.map( (i) => {
        id = document.getElementById(`id${i}`);
        scrollHeight = id.scrollHeight;
        offsetTop = id.offsetTop;
        top = offsetTop - domHight > 0 ? offsetTop - domHight : 0;
        bottom = scrollHeight + offsetTop;
        // 页面滚动位置 > 元素距离顶部高度-窗口高度 && 页面滚动位置 < 元素距离顶部高度+元素本身高度
        if (scrollTop >= top && scrollTop <= bottom) {
          console.log('元素出现在可视区: ' + i);
        } else {
          console.log('元素不在了: ' + i);
        }
      });
    },
  },
}
</script>

<style lang='less' scoped>
  .ulBox {
    width: 100%;
    // height: 100vh;
    // overflow-y: scroll;
    margin: 0;
    padding: 0;
    list-style: none;
    .li {
      width: 100%;
      height: 5rem;
      border: 1px solid #999999;
      display: flex;
      justify-content: center;
      align-items: center;
    } 
    .li:not(:first-child) {
      border-top: none;
    }
  }
</style>