<el-select v-selectMore="loadMore">...</el-select>

const selectMore = {
  bind(el, binding) {
    // 获取element-ui定义好的scroll盒子
    let select_dom = el.querySelector('.el-select-dropdown .el-select-dropdown__wrap');
    select_dom.addEventListener('scroll', function () {
      const CONDITION = this.scrollHeight - this.scrollTop <= this.clientHeight;
      if (CONDITION) {
        binding.value();
      }
    });
  }
};

export default selectMore;