element el-tree折叠收缩

<h3>
  <span>el-tree折叠收缩 </span>
   <el-tooltip class="item" effect="dark" :content="treeBtn.iconTip" placement="top">
     <svg-icon :icon-class="treeBtn.iconClass" @click="toggleEltree"></svg-icon>
   </el-tooltip>
 </h3>
 <el-row>
   <el-col :span="3">
     <el-tree 
       ref="elTree" 
       :data="data" 
       :props="defaultProps" 
       node-key="id"
       :default-expand-all="expandNode">
     </el-tree>
   </el-col>
 </el-row>

export default {
	data() {
	    return {
	      treeBtn: {
	        iconClass: 'fullscreen',
	        iconTip: '展开'
	      },
	      expandNode: false,
	      defaultProps: {
	        children: 'children',
	        label: 'label'
	      },
	      data: [
	        {
	          label: '一级 1',
	          id: 98543,
	          children: [{
	            label: '二级 1-1',
	            id: 98343,
	            children: [{
	              label: '三级 1-1-1',
	              id: 98043,
	            }]
	          }]
	        },
	        {
	          label: '一级 2',
	          id: 98545,
	          children: [{
	            label: '二级 2-1',
	            id: 45545,
	            children: [{
	              label: '三级 2-1-1',
	              id: 44456,
	            }]
	          }]
	        }
	   ]
	},
	methods: {
		toggleEltree() {
	      this.expandNode = !this.expandNode
	      if(this.expandNode) {
	        this.treeBtn.iconClass = 'exit-fullscreen'
	        this.treeBtn.iconTip = '收缩'
	      } else {
	        this.treeBtn.iconClass = 'fullscreen'
	        this.treeBtn.iconTip = '展开'
	      }
	
	      let allNodes = this.$refs.elTree.store.nodesMap;
	      for (let x in allNodes) {
	        allNodes[x].expanded = this.expandNode;
	      }
	    }
	}
}