elementUI-tree组件 懒加载

<el-tree ref="tree" :data="menu.treeData" :props="menu.defaultProps"
                                         :filter-node-method="filterNode"
                                         :expand-on-click-node="false"
                                         :load="loadTreeNodes"
                                         lazy
                                         @node-click="handleNodeClick">

 loadTreeNodes: function (node, resolve) {
                if (node.level === ) { // 第一次调用
                    return resolve(this.doLoadTreeNodes(""));
                }
                if (node.level >= ) { // 点击之后触发
                    return resolve(this.doLoadTreeNodes(node.data.id));
                }
            },