下面的需求如何实现？

Question

let arr =[
        {
            "userId":20,
            "userName":"444",
            "itemStyle":true,
            "deptId":12
        },
        {
            "userId":22,
            "userName":"NONALPF001adminAL1",
            "itemStyle":true,
            "deptId":12
        },
        {
            "userId":1,
            "userName":"admin",
            "itemStyle":true,
            "deptId":7
        }
    ]


let arr2 = [
    {
        "deptId":7,
        "deptName":"系统管理部",
        "userList":[

        ],
        "isChecked":false,
        "listStyle":true
    },
    {
        "deptId":12,
        "deptName":"分析师",
        "userList":[
            {
                "userId":23,
                "userName":"NONALPF004adminAL1",
                "itemStyle":true,
                "deptId":12
            },
            {
                "userId":24,
                "userName":"NONALPF001adminAL2",
                "itemStyle":true,
                "deptId":12
            }]
    },
    {
        "deptId":13,
        "deptName":"外包人员",
        "userList":[
            {
                "userId":89,
                "userName":"NONALPF010adminAL2",
                "itemStyle":true
            },
            {
                "userId":90,
                "userName":"NONALPF010adminAL3",
                "itemStyle":true
            },
            {
                "userId":193,
                "userName":"NONALPF009adminMem6",
                "itemStyle":true
            }
        ],
        "isChecked":false,
        "listStyle":true
    }
]


如何通过arr的每一项里的deptId，把arr的每一项放在arr2的对应的deptId的那一项的userList中呢？
要求不使用普通的for循环或者forEach。尽量使用一下高级的写法，或者是es6,7,8的写法？

Answer 1

啥叫高级的写法
通常管接收一个函数作为参数的函数叫做高阶函数
你不能因为你天天用foreach就看不起人家
它可是正儿八经的es6提出的高阶函数