vue如何实现el-select下拉选项的懒加载

interface IScrollOption {
  distance: number; // 触发loadData事件的滚轴距底部的距离
  loadData: () => void; // 数据加载函数
}

function handleScroll(dom: Element, option: IScrollOption) {
  //
  const scrollBottom = dom.scrollTop + dom.clientHeight;
  if (dom.scrollHeight - scrollBottom <= option.distance) {
    // 数据加载
    option.loadData();
  }
}

<el-select v-model="selectData">
  <el-option v-for="item in data" :key="item.id" value="item.id" :label="item.name"></el-option>
</el-select>

import Vue from "vue";
import { throttle } from "lodash";
export interface ILazyProps {
  loadData: () => void; // 数据加载函数
  distance: number; // 触发函数调用的滚动距离
  scrollBody?: string; // 置顶滚动容器 , 不指定则为指令绑定元素
  callback: (fn: () => void) => void; // 自定义回调逻辑,可用于适时销毁监听事件
}
Vue.directive("lazy-load", {
  
  inserted: (el, binding) => {
    // 获取scroll 滚动的容器元素,由参数传入
    // 如果没有传入,则默认绑定指令的元素自己
    // 获取懒加载处理函数 , 以及其他参数
    const { loadData, distance, scrollBody, callback } =
      binding.value as ILazyProps;
    let scrollContainer = el;
    if (scrollBody) {
      scrollContainer = el.querySelector(scrollBody) || el;
    }
    // 滚动事件监听
    const scroll = throttle(
      handleScroll.bind(null, scrollContainer, { distance, loadData }),
      500
    );
    scrollContainer.addEventListener("scroll", scroll);
    // 回调时 返回事件销毁函数
    callback(() => {
      scrollContainer.removeEventListener("scroll", scroll);
    });
  },
});

<el-select v-model="selectData" v-lazy-load="lazyOption">
  <el-option v-for="item in data" :key="item.id" value="item.id" :label="item.name"></el-option>
</el-select>

import { ILazyProps } from "@/directives/lazyLoad";
export default class extends Vue {
  lazyOption: ILazyProps = {
    loadData: this.loadData,
    distance: 20,
    scrollBody: ".el-scrollbar__wrap", // 为el-select 滚动容器的DOM元素的class选择器
    callback: (fn: () => void) => {
    	// 这里是在组件销毁前, 移除监听事件.
      this.$once("hook:beforeDestroy", () => fn());
    },
  };
	loadData(): void {
    this.data = this.data.concat(
      new Array(5).fill({
        id: "1009",
        name: "双十一",
      })
    );
  }
}

<div v-infinite-scroll="loadData" infinite-scroll-disabled="disabled" infinite-scroll-delay="delay">
    <table
      :showPagination="false"
      :tableOption="tableOption"
      :tableColumns="tableColumns"
    ></table>
</div>

export default {
  name: 'InfiniteScroll',
  inserted(el, binding, vnode) {
    // 绑定的回调函数
    const cb = binding.value;
		// 当前组件实例引用
    const vm = vnode.context;
    // only include vertical scroll
    // 滚动容器DOM元素
    const container = getScrollContainer(el, true);
    // 获取指令需要的参数 delay distance immediate disabled 
    const { delay, immediate } = getScrollOptions(el, vm);
    // 滚动事件处理函数,节流
    const onScroll = throttle(delay, handleScroll.bind(el, cb));
		// 将额外的计算属性绑定到el上,在unbind 可用于移除监听函数
    el[scope] = { el, vm, container, onScroll };
    if (container) {
      container.addEventListener('scroll', onScroll);
      if (immediate) {
        // 容器内元素发生节点变更时触发执行
        // MutationObserver API 功能调用
        const observer = el[scope].observer = new MutationObserver(onScroll);
        observer.observe(container, { childList: true, subtree: true });
        // 初始调用一次滚动加载函数
        onScroll();
      }
    }
  },
  unbind(el) {
    // 移除滚动事件
    const { container, onScroll } = el[scope];
    if (container) {
      container.removeEventListener('scroll', onScroll);
    }
  }
};