关于flatMap的用法

//从一个总的行政区里面将所有行政区平铺
let districtCode = [
  {
    "id": 1,
    "code": "350400",
    "name": "三明市",
    "grade": "city",
    "orderNo": 1,
    "parentCode": null,
    "children": [
      {
        "id": 8,
        "code": "350426",
        "name": "尤溪县",
        "grade": "county",
        "orderNo": 7,
        "parentCode": "350400",
        "children": []
      },
      {
        "id": 12,
        "code": "350430",
        "name": "建宁县",
        "grade": "county",
        "orderNo": 11,
        "parentCode": "350400",
        "children": []
      },
      {
        "id": 11,
        "code": "350429",
        "name": "泰宁县",
        "grade": "county",
        "orderNo": 10,
        "parentCode": "350400",
        "children": []
      },
      {
        "id": 9,
        "code": "350427",
        "name": "沙县",
        "grade": "county",
        "orderNo": 8,
        "parentCode": "350400",
        "children": []
      },
      {
        "id": 2,
        "code": "350402",
        "name": "梅列区",
        "grade": "county",
        "orderNo": 1,
        "parentCode": "350400",
        "children": []
      },
      {
        "id": 4,
        "code": "350421",
        "name": "明溪县",
        "grade": "county",
        "orderNo": 3,
        "parentCode": "350400",
        "children": []
      },
      {
        "id": 7,
        "code": "350425",
        "name": "大田县",
        "grade": "county",
        "orderNo": 6,
        "parentCode": "350400",
        "children": []
      },
      {
        "id": 5,
        "code": "350423",
        "name": "清流县",
        "grade": "county",
        "orderNo": 4,
        "parentCode": "350400",
        "children": []
      },
      {
        "id": 10,
        "code": "350428",
        "name": "将乐县",
        "grade": "county",
        "orderNo": 9,
        "parentCode": "350400",
        "children": []
      },
      {
        "id": 13,
        "code": "350481",
        "name": "永安市",
        "grade": "county",
        "orderNo": 12,
        "parentCode": "350400",
        "children": []
      },
      {
        "id": 3,
        "code": "350403",
        "name": "三元区",
        "grade": "county",
        "orderNo": 2,
        "parentCode": "350400",
        "children": []
      },
      {
        "id": 6,
        "code": "350424",
        "name": "宁化县",
        "grade": "county",
        "orderNo": 5,
        "parentCode": "350400",
        "children": []
      }
    ]
  }
]
let test = districtCode.flatMap(d => {
                return [d].concat(d.children)
            })

结果

又一个例子

把这个数组对象的每个属性拼接并且按照需要组合成一个新的数组返回

let currentPayLoads = this.flightTasks.find(f=>f.id == this.taskId)!.payloads
let a = currentPayLoads.flatMap((p)=>{
            if(p.liveReadingDefinitions == null) {
                return []
            }
            return p.liveReadingDefinitions.map(d=>{
                return {
                    title: d.name,
                    prop: `readings.${d.index}`
                }
            })
        })
  console.log("a", a)

结果