VirtualList组件

<template>
  <div
    ref="vList"
    class="vl-container"
    :style="{ height: clientHeight + 'px' }"
  >
    <div class="vl-wrap" :style="{ height: vlHeight + 'px' }">
      <div
        class="vl-item"
        :style="{
          height: rowHeight + 'px',
          lineHeight: rowHeight + 'px',
          top: setTop(index) + 'px',
        }"
        v-for="(v, index) in visibleData"
        :key="v.index"
      >
        <template v-if="$scopedSlots.default">
          <slot :data="v"></slot>
        </template>
        <template v-else>{{ v.name }}</template>
      </div>
    </div>
  </div>
</template>

<script>
import { debounce } from "@/utils";
export default {
  props: {
    // 缓冲的数量(前后各缓存2个)
    bufferCount: {
      type: Number,
      default: 2,
    },
    data: {
      // 测试数据
      type: Array,
      default: () => {
        return Array(1000)
          .fill("")
          .map((v, i) => {
            return { name: i + 1, age: 11 };
          });
      },
    },
    clientHeight: {
      // 显示容器的高度
      type: Number,
      default: 300,
    },
    rowHeight: {
      // Item的高度
      type: Number,
      default: 50,
    },
  },
  data() {
    return {
      pageSize: 0, // 可视区域Item的个数
      scrollTop: 0, // 显示容器的scrollTop
      offsetIndex: 0, // 滚出去的Item的个数（往下取整）
    };
  },
  computed: {
    vlHeight() {
      return this.data.length * this.rowHeight; // List容器的真实高度
    },
    // 展示数据
    visibleData() {
      this.pageSize = Math.ceil(this.clientHeight / this.rowHeight); // 相当于pageSize
      this.offsetIndex = Math.floor(this.scrollTop / this.rowHeight); // 滚出去的Item的个数

      // console.log(this.offsetIndex, "this.offsetIndex");

      let startIndex =
        this.offsetIndex >= this.bufferCount
          ? this.offsetIndex - this.bufferCount
          : 0;

      let lastIndex = this.pageSize + this.offsetIndex + this.bufferCount;

      let endIndex =
        lastIndex > this.data.length ? this.data.length : lastIndex;

      return this.data.slice(startIndex, endIndex);
    },
  },
  mounted() {
    this.$refs.vList.addEventListener(
      "scroll",
      debounce(() => {
        this.scrollTop = this.$refs.vList.scrollTop;
      }, 10),
      false
    );
  },
  methods: {
    setTop(index) {
      if (this.offsetIndex > this.bufferCount) {
        return this.rowHeight * (index + this.offsetIndex - this.bufferCount);
      } else {
        return this.rowHeight * index;
      }
    },
  },
};
</script>
<style scoped>
.vl-container {
  border: 2px solid #0094ff;
  overflow: auto;
}
.vl-container > .vl-wrap {
  overflow: hidden;
  position: relative;
}
.vl-container > .vl-wrap > .vl-item {
  position: absolute;
  width: 100%;
  box-sizing: border-box;
  border-bottom: 1px dotted red;
  background-color: #e7e7be;
}
</style>