当获取后台数据为空时，列表显示默认空图片，不正确姿势：

    <el-table
      v-loading="isLoading"
      :data="deviceListData"
      style="width: 100%"
      :header-cell-style="headStyle"
      row-key="id"
      @row-click="handleTabSel"
    >
      <template v-if="deviceListData.length">
        <el-table-column prop="name" label="设备名称"> </el-table-column>
        <el-table-column prop="id" label="设备ID"> </el-table-column>
        <el-table-column prop="online" label="在线状态"> </el-table-column>
        <el-table-column prop="1656121597" label="激活时间"> </el-table-column>
        <el-table-column label="操作">
          <div class="op-wrapper">
            <div @click="editDevice" class="edit">编辑</div>
            <div @click="controlDevice" class="edit">控制</div>
            <div @click="deleteDevice" class="edit">移除</div>
          </div>
        </el-table-column>
      </template>
      <el-empty v-else image-size="60"></el-empty>
    </el-table>

发现el-empty 默认空图片一直显示不出来，还以为el-empty用法有问题，弄了个空页面，直接加载el-empty 发现没有问题。查了一下原来el-table 数据为空时，显示默认图片写法不对，正确姿势如下：

    <el-table
      v-loading="isLoading"
      :data="deviceListData"
      style="width: 100%"
      :header-cell-style="headStyle"
      row-key="id"
      @row-click="handleTabSel"
    >
      <el-table-column prop="name" label="设备名称"> </el-table-column>
      <el-table-column prop="id" label="设备ID"> </el-table-column>
      <el-table-column prop="online" label="在线状态"> </el-table-column>
      <el-table-column prop="1656121597" label="激活时间"> </el-table-column>
      <el-table-column label="操作">
        <div class="op-wrapper">
          <div @click="editDevice" class="edit">编辑</div>
          <div @click="controlDevice" class="edit">控制</div>
          <div @click="deleteDevice" class="edit">移除</div>
        </div>
      </el-table-column>
      <template slot="empty">
        <el-empty image-size="60"></el-empty>
      </template>
    </el-table>    

这样就能正常显示el-emtpy 默认空图片了。