// directives.js

import Vue from 'vue'
Vue.directive('loadmore', {
 bind (el, binding) {
  // 获取element-ui定义好的scroll盒子
  const SELECTWRAP_DOM = el.querySelector('.el-select-dropdown .el-select-dropdown__wrap')
  SELECTWRAP_DOM.addEventListener('scroll', function () {
   
   const CONDITION = this.scrollHeight - this.scrollTop <= this.clientHeight
   if (CONDITION) {
    binding.value()
   }
  })
 }
})

// main.js
// 注册滚动条加载触发事件v-loadmore绑定
import directives from './directives'
Vue.use(directives)

<!-- vue -->
<el-select
 v-model="chatmode"
 placeholder="聊天模式"
 size="mini"
 v-loadmore="loadMore">
 <el-option
  v-for="item in chatmodes"
  :key="item.value"
  :label="item.qa_name"
  :value="item.qa_code"
  :disabled="item.disabled">
 </el-option>
</el-select>
<script>
export default {
 methods: {
  loadMore () {
   // 这里写入要触发的方法
  }
 }
}
</script>