vue模拟聊天页面列表：滚动到底部，滚动到顶部触发加载更多

先看下效果：

代码：

<template>
  <div>
    <div style="text-align: center">
      <button @click="scrollTop">滚动到顶部button>
      <button @click="scrollBottom">滚动到底部button>
    div>

    <div class="scroll_wrap" ref="scrollWrap">
      <div v-for="(s, i) in list" :key="i" class="item">{{ s }}div>
    div>
  div>
template>

<script>
export default {
  data() {
    return {
      list: [],
      noMore: false, //暂无更多数据
    };
  },
  mounted() {
    this.initData();
    this.scrollBottom();
    this.$refs.scrollWrap.addEventListener("scroll", this.onScrollListener);
  },
  methods: {
    //滚动监听
    onScrollListener() {
      if (this.$refs.scrollWrap.scrollTop == 0) {
        console.log("滚动到顶部了");
        
        if (this.noMore) {
          this.$baseUI.showToast("暂无更多数据");
          return;
        }

        this.$baseUI.showLoading();
        
        //模拟耗时任务从接口获取数据
        setTimeout(() => {
          const scrollWrap = this.$refs.scrollWrap;

          let h1 = scrollWrap.scrollHeight;
          console.log("h1======" + h1);

          this.loadMoreData();
          this.$baseUI.hideLoading();

          //list更新后，等待页面渲染完毕再去拿scrollHeight,否则拿到的是之前的
          this.$nextTick(() => {
            let h2 = scrollWrap.scrollHeight;
            console.log("h======" + h2);
			
			//顶部在原先基础上往下滚动50px，露出新加载数据的一点	
            scrollWrap.scrollTo({
              top: h2 - h1 - 50,
              behavior: "instant", //auto-自动滚动 instant-瞬间滚动 smooth-平滑滚动
            });
          });
        }, 1000);
      }
    },
    //滚动到顶部
    scrollTop() {
      this.$nextTick(() => {
        const scrollWrap = this.$refs.scrollWrap;
        scrollWrap.scrollTo({
          top: 0,
          behavior: "smooth", //auto-自动滚动 instant-瞬间滚动 smooth-平滑滚动
        });
      });
    },
    //滚动到底部
    scrollBottom() {
      this.$nextTick(() => {
        let scrollWrap = this.$refs.scrollWrap;
        scrollWrap.scrollTo({
          top: scrollWrap.scrollHeight,
          behavior: "smooth", //auto-自动滚动 instant-瞬间滚动 smooth-平滑滚动
        });
      });
    },
    //加载更多数据
    loadMoreData() {
      let arr = [];
      for (let i = this.list.length; i < 10 + this.list.length; i++) {
        arr.unshift("data --- " + i);
      }
      this.list = [...arr, ...this.list];

      if (this.list.length == 40) {
        this.noMore = true; //数据全部加载完毕
      }
    },
    //初始化数据
    initData() {
      for (let i = 0; i < 20; i++) {
        this.list.unshift("data --- " + i);
      }
    },
  },
  beforeDestroy() {
    this.$refs.scrollWrap.removeEventListener("scroll", this.onScrollListener);
  },
};
script>

<style lang="less" scoped>
.scroll_wrap {
  width: 300px;
  height: 500px;
  position: absolute;
  top: 30px;
  left: 50%;
  transform: translateX(-50%);
  border: 1px solid #333;
  overflow: auto;

  .item {
    height: 50px;
    line-height: 50px;
    padding-left: 15px;
    border-bottom: 1px solid #e4e4e4;
  }
}
style>