js格式化树形数据（扁平化数据）

需求：

1、把如下数据按照parent_id等于id的规则建立父子关系
2、同一层级的数组按照order升序

[ { "id": 1, "name": "estate", "title": "物业管理", "type": "nav", "leave": 1, "order": 1, "parent_id": 0, "url": "/estate" },
 { "id": 2, "name": "house", "title": "费用管理", "type": "nav", "leave": 2, "order": 1, "parent_id": 1, "url": "estate" },
 { "id": 3, "name": "temporaryCharges", "title": "临时收费", "type": "nav", "leave": 3, "order": 1, "parent_id": 2, "url": "charge" }, 
{ "id": 4, "name": "propertyFees", "title": "物业费", "type": "nav", "leave": 3, "order": 2, "parent_id": 2, "url": "propertyFees" },
 { "id": 6, "name": "propertyFeesEdit", "title": "编辑", "type": "handle", "leave": 4, "order": 2, "parent_id": 4, "url": null },
 { "id": 7, "name": "propertyFeesLogs", "title": "记录", "type": "handle", "leave": 4, "order": 3, "parent_id": 4, "url": null },
 { "id": 8, "name": "propertyFeesPayment", "title": "缴费", "type": "handle", "leave": 4, "order": 4, "parent_id": 4, "url": null },
 { "id": 9, "name": "carFees", "title": "停车费", "type": "nav", "leave": 3, "order": 3, "parent_id": 2, "url": "carFees" },
 { "id": 11, "name": "carFeesLogs", "title": "记录", "type": "handle", "leave": 4, "order": 2, "parent_id": 9, "url": null },
 { "id": 12, "name": "carFeesPayment", "title": "缴费", "type": "handle", "leave": 4, "order": 3, "parent_id": 9, "url": null },
 { "id": 13, "name": "gain", "title": "固定收益", "type": "nav", "leave": 3, "order": 4, "parent_id": 2, "url": "gain" },
 { "id": 14, "name": "bill", "title": "账单管理", "type": "nav", "leave": 2, "order": 2, "parent_id": 1, "url": "estate" },
......]

最终效果：

[{
	"id": 1,
	"name": "estate",
	"title": "物业管理",
	"type": "nav",
	"leave": 1,
	"order": 1,
	"parent_id": 0,
	"url": "/estate",
	"children": [{
		"id": 2,
		"name": "house",
		"title": "费用管理",
		"type": "nav",
		"leave": 2,
		"order": 1,
		"parent_id": 1,
		"url": "estate",
		"children": [{
			"id": 3,
			"name": "temporaryCharges",
			"title": "临时收费",
			"type": "nav",
			"leave": 3,
			"order": 1,
			"parent_id": 2,
			"url": "charge"
		}, {
			"id": 4,
			"name": "propertyFees",
			"title": "物业费",
			"type": "nav",
			"leave": 3,
			"order": 2,
			"parent_id": 2,
			"url": "propertyFees",
			"children": [{
				"id": 6,
				"name": "propertyFeesEdit",
				"title": "编辑",
				"type": "handle",
				"leave": 4,
				"order": 2,
				"parent_id": 4,
				"url": null
			}, {
				"id": 7,
				"name": "propertyFeesLogs",
				"title": "记录",
				"type": "handle",
				"leave": 4,
				"order": 3,
				"parent_id": 4,
				"url": null
			}
.......
	}
}]

实现代码：

'use strict';
exports.formatRouter = {

  /**
   * 树形数据格式化，其中：
   * 子级的’parent_id‘等于父级的id,
   * 最高父级的id为0
   *
   * 排序规则为‘order’的数字顺序
   * */
  treeData(data) {
    // 对源数据深度克隆
    const cloneData = JSON.parse(JSON.stringify(data));
    // filter嵌套filter相当于for循环嵌套for循环
    const result = cloneData.filter(parent => {
      // 返回每一项的子级数组
      const branchArr = cloneData.filter(child => parent.id === child.parent_id);

      // 若子级存在，则给子级排序；且，赋值给父级
      if (branchArr.length > 0) {
        branchArr.sort(this.compare('order'));
        parent.children = branchArr;
      }
      // 返回最高的父级，即，parent_id为0，
      return parent.parent_id === 0;
    });
    // 给最高级的父级排序
    result.sort(this.compare('order'));
    return result;
  },
  // 对象数组排序
  compare(property) {
    return function(a, b) {
      const value1 = a[property];
      const value2 = b[property];
      return value1 - value2;// 升序,降序为value2 - value1
    };
  },
};

说明：

其实就是两个for循环嵌套，性能上还没有for循环好。

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