js对象-平铺与嵌套的互相转换

一个json对象，包含嵌套关系，传输过来的时候是平铺的，顺序打乱，用parentCode属性来关联，如下

{
    "1":{
        "name": "中国",
        "code": "1",
        "parentCode":"0"
    },
    "12":{
        "name": "上海",
        "code": "12",
        "parentCode":"1"
    },
    "121":{
        "name": "杨浦区",
        "code": "121",
        "parentCode":"12"
    },
    "13":{

        "name": "南京",
        "code": "13",
        "parentCode":"1"
    },

    "122":{ 
      "name": "嘉定区", 
      "code": "122", 
      "parentCode":"12" 
    } 
}

parentCode位0的对象是根对象，要求把平铺对象转换成这样的嵌套对象

[
    {
        "name": "中国",
        "code": "1",
        "parentCode":"0",
        "children":[
            {
                "name": "上海",
                "code": "12",
                "parentCode":"1",
                "children":[
                    {
                        "name": "杨浦区",
                        "code": "121",
                        "parentCode":"12"
                    },
                    {
                        "name": "嘉定区",
                        "code": "122",
                        "parentCode":"12"
                    }
                ]
            },
            {
                "name": "南京",
                "code": "13",
                "parentCode":"1"
            }
        ]
    }
]

思路：

对象是引用变量，直接遍历添加即可，无需按照层级顺序从外到内添加。

function transfer(origin){
    var root = null;
    Object.keys(origin).forEach(key => {
        var obj = origin[key]
        if (obj.parentCode === '0') {
            root = obj;
            return
        }
        var parent = origin[obj.parentCode];
        !parent.children && (parent.children = [])
        parent.children.push(obj)
    })
    return root
}