elementui 樹形表格懶加載與全部摺疊

<div id="app">
    <el-table ref="tabletree" size="mini"
              :data="data"
              :height="tableheight"
              row-key="code"
              border
              v-loading="loading"
              lazy
              :load="list"
              :tree-props="{children: 'children', hasChildren: 'hasChildren'}">
        <el-table-column prop="name" label="名稱" width="300" header-align="center">
            <template slot="header">
                名稱
                <el-link type="primary" v-on:click="fold" style="float:right;">摺疊全部</el-link>
            </template>
        </el-table-column>
        <el-table-column prop="code" label="代碼" width="100" align="center"></el-table-column>
        <el-table-column width="200" align="center">
            <template slot="header" slot-scope="scope">
                <el-link type="primary" v-on:click="addRoot">新建根項</el-link>
            </template>
            <template slot-scope="scope">
                <el-button-group>
                    <el-link type="primary" v-on:click="addChild(scope.row)">新建子項</el-link>
                    <el-link type="warning" v-on:click="edit(scope.row)">修改</el-link>
                    <el-link type="danger" v-on:click="del(scope.row.code)">刪除</el-link>
                </el-button-group>
            </template>
        </el-table-column>
        <el-table-column></el-table-column>
    </el-table>
</div>

<script>
    new Vue({
        el: '#app',
        data() {
            return {
                data: [],
                loading: false,
                tableheight: 500
            }
        },
        methods: {
            list(tree, treeNode, resolve) {
                var that = this;
                this.loading = true;
                $.post('/admin_areas/code/listXzqh', { parentcode: tree ? tree.code : null }, function (res) {
                    accecpResult(res, function () {
                        if (treeNode) {
                            resolve(res.data);
                        } else {
                            that.data = res.data;
                        }
                        that.loading = false;
                    })
                })
            },
            fold() {
                var els = this.$el.getElementsByClassName('el-table__expand-icon el-table__expand-icon--expanded')
                for (var i = 0; i < els.length; i++) {
                    els[i].click()
                }
            },
            addRoot() {

            },
            addChild(row) {
                
            },
            edit(row) {

            },
            del(code) {

            }
        },
        mounted() {
            this.list();
            this.$nextTick(function () {
                this.tableheight = window.innerHeight - 10;
                var self = this;
                window.onresize = function () {
                    self.tableheight = window.innerHeight - 10;
                }
            })
        }
    });
</script>

注：
1、hasChildren屬性必須，children也必須，不過可以通過tree-props設置屬性名稱
2、list方法中判斷treeNode是否爲undifined來確定是初次加載還是展開後加載，初次加載要賦值，展開後加載需使用resolve加入數據。
3、實測中，expand-change事件觸發不了，toggleRowExpansion方法也不可用，百度後得知觸發箭頭圖標的點擊事件即可，因此在fold方法中通過已展開的圖標樣式類名查找，然後模擬點擊