实现效果与原理

我们希望实现鼠标移动至树型结构的结点上就显示按钮，移出就隐藏按钮
 
实现原理：是通过@mouseenter 和 @mouseleave两个属性来控制鼠标hover的效果，再配合v-show来控制是否展示你需要的控件

具体代码

<el-tree
  :data="data"
  ref="tree"
  default-expand-all
  node-key="id"
  :expand-on-click-node="false">
  <span class="custom-tree-node" slot-scope="{ node, data }" @mouseenter="mouseenter(data)" @mouseleave="mouseleave(data)">
    <span>{{ node.label }}</span>
    <span>
      <el-tooltip v-show="data.show" class="item" effect="dark" content="文字提示" placement="top">
        <el-button
          type="text"
          size="mini"
          @click="() => append(data)"
          icon="el-icon-plus"
        >
        </el-button>
      </el-tooltip>
      <el-dropdown v-show="data.show" @command="handleCommand">
        <span class="el-dropdown-link">
          <i class="el-icon-more"></i>
        </span>
        <el-dropdown-menu slot="dropdown">
          <el-dropdown-item command="addFolder">新增文件夹</el-dropdown-item>
          <el-dropdown-item command="edit">编辑</el-dropdown-item>
          <el-dropdown-item command="delete">删除</el-dropdown-item>
        </el-dropdown-menu>
      </el-dropdown>
    </span>
  </span>
</el-tree>
<script>
export default {
  data() {
    const data = [{
      id: 1,
      label: '一级 1',
      children: [{
        id: 4,
        label: '二级 1-1',
      }]
    }, {
      id: 2,
      label: '一级 2',
      children: [{
        id: 5,
        label: '二级 2-1',
      }, {
        id: 6,
        label: '二级 2-2',
      }]
    }, {
      id: 3,
      label: '一级 3',
      children: [{
        id: 7,
        label: '二级 3-1',
      }, {
        id: 8,
        label: '二级 3-2',
      }]
    }]
    return {
      defaultProps: {
        children: 'children',
        label: 'label'
      },
      data: JSON.parse(JSON.stringify(data))
    }
  },
  methods: {
    mouseenter(data) {
      this.$set(data, 'show', true)
    },
    mouseleave(data) {
      this.$set(data, 'show', false)
    },
  }
}
</script>