<el-tree
      ref="tree"
      lazy
      :load="load"
      highlight-current
      @node-click="handleNodeClick"
      :expand-on-click-node="false"
      :node-key="key"
      :props="defaultProps"
      :current-node-key="currentNodeKey"
    >
   </el-tree>

  methods: {
    /** 傳遞一個(gè)懶加載函數(shù)給el-tree組件 */
    load(node, resolve) {
      this.chooseNode = node;
      // 這里后端給的數(shù)據(jù)唯一標(biāo)識(shí)不是id，是key，根據(jù)個(gè)人數(shù)據(jù)修改
      this.getTreeData(node.level, node.data.key, resolve);
    },
    /** 懶加載樹節(jié)點(diǎn)數(shù)據(jù)處理函數(shù) */
    async getTreeData(level, key, resolve) {
      if (level === 0) {
        this.loading = true;
        const { data: res } = await http.post('getTreeNode');
        if (res.code === 200 && res.data && res.data.length) {
          this.treeData = this.treeArrayToArray(res.data);
          resolve(res.data);
          this.$nextTick(() => {
            // 零級(jí)的第一個(gè)子節(jié)點(diǎn)，也就是第一級(jí)的第一個(gè)節(jié)點(diǎn)
            let nodedata = this.chooseNode.childNodes[0];
            nodedata.expanded = true;
            // 再次觸發(fā)load方法
            nodedata.loadData();
            // 注意，因?yàn)樯戏皆俅斡|發(fā)load方法，走了this.chooseNode = node;這一步，所以這里的 this.chooseNode指向的是零級(jí)的子節(jié)點(diǎn)，也就是第一級(jí)，這里的`this.chooseNode.childNodes[0]`表示的是是第二級(jí)的第一個(gè)節(jié)點(diǎn)
            this.currentNodeKey = this.chooseNode.childNodes[0].data.key;
            this.handleNodeClick(this.chooseNode.childNodes[0].data);
          });
        } else {
          resolve([]);
        }
        this.loading = false;
      } else {
        // 根據(jù)key去找到點(diǎn)擊樹節(jié)點(diǎn)的children數(shù)組，加載數(shù)據(jù)到其下
        const currentNode = this.treeData.find(item => item.key === key);
        if (currentNode.children && currentNode.children.length) {
          resolve(currentNode.children);
        } else {
          resolve([]);
        }
      }
    },
    /** 樹結(jié)構(gòu)數(shù)組轉(zhuǎn)換成扁平數(shù)組 */
    treeArrayToArray(tree) {
      const arr = [];
      function recursiveFunction(tree) {
        for (let i = 0; i < tree.length; i++) {
          // 給所有沒有子節(jié)點(diǎn)的節(jié)點(diǎn)添加leaf屬性，該屬性用來取消左側(cè)小箭頭
          if (!(tree[i].children && tree[i].children.length)) {
            tree[i].leaf = true;
          }
          arr.push(tree[i]);
          if (tree[i].children && tree[i].children.length) {
            recursiveFunction(tree[i].children);
          }
        }
      }
      recursiveFunction(tree);
      return arr;
    },
    /** 獲取點(diǎn)擊樹節(jié)點(diǎn)的數(shù)據(jù)，進(jìn)行渲染右側(cè)頁面等操作 */
    handleNodeClick(data) {
    },
  },