js 操作数组合并数组内相同值下面的子数组

合并数组下相同类型的子数组 ：

let arr = [
    {
        type: 1, 
        arrSon: [
            {
                id: 1,
                msg: 'asdad112312as'
            },
            {
                id: 2,
                msg: '131231dadas'
            }
        ]
    },
    {
        type: 1,
        arrSon: [
            {
                id: 3,
                msg: 'asdada23s'
            },
            {
                id: 4,
                msg: '131231dadas'
            }
        ]
    },
    {
        type: 2,
        arrSon: [
            {
                id: 5,
                msg: 'asda112das21'
            }
        ]
    },
    {
        type: 2,
        arrSon: [
            {
                id: 6,
                msg: '13asd32asdadas'
            },
            {
                id: 7,
                msg: '11asd2a1fsdadas'
            }
        ]
    },
    {
        type: 3,
        arrSon: [
            {
                id: 8,
                msg: '1as3d2asdadas'
            }
        ]
    }
]

let obj = {}
let newArr = []
arr.forEach(item => {
   if (!obj[item.type]) {
      obj[item.type] = {}
      obj[item.type].type = item.type
      obj[item.type].arrSon = []
      newArr.push(obj[item.type])
   }
   console.log('obj[item.type]', obj[item.type])
   obj[item.type].arrSon = obj[item.type].arrSon.concat(item.arrSon)
})
console.log(newArr)