Reduce recordset to array of same keys with nested array of objects

Question

I have a data set that I query from a database that gives the following object.

[{
    item_id: 'adsfsdf',
    order_no: '2499321',
    line_no: 8,
    uom: 'EA',
    qty: 0,
    req_date: 2021-06-07T00:00:00.000Z,
    tracking: 'asdfsad',
    carrier_name: 'UPS Ground',
    carrier_address: 'asdf'
  },
  {
    item_id: 'asdfasdf',
    order_no: '2499321',
    line_no: 9,
    uom: 'EA',
    qty: 2,
    req_date: 2021-06-07T00:00:00.000Z,
    tracking: 'asdf',
    carrier_name: 'UPS Ground',
    carrier_address: 'asdfasdf'
  },
  {
    item_id: 'asdfsdf',
    order_no: '2499903',
    line_no: 1,
    uom: 'EA',
    qty: 4,
    req_date: 2021-06-04T00:00:00.000Z,
    tracking: null,
    carrier_name: 'UPS Ground',
    carrier_address: 'asdfasdfa'
  }]

I would like to reduce the array into a smaller array grouped by the order_no value.

So far, I have something like this:

request.query(q).then(function (res) {
            let newObj = []
            res.recordset.forEach((e) => {
                newObj.push({[e.order_no] : [e]})
            })

            let finalObj = newObj.reduce((a, obj) => {
                let [k, v] = Object.entries(obj)[0]
                a[k] = a[k] + v
                return a
            }, {})

            let final = Object.entries(finalObj).map(([k,v]) => {
                return {[k]:v}
            })
            
            dbConn.close();
        }).catch(function (err) {
            console.log(err);
            dbConn.close();
        });

When I console.log the "final" variable, this is how it looks:

{
    '2499321': 'undefined[object Object][object Object][object Object][object Object][object Object][object Object][object Object][object Object][object Object]'
  },
  { '2499903': 'undefined[object Object]' },
  { '2501438': 'undefined[object Object][object Object]' },
  { '2501803': 'undefined[object Object][object Object]' },
  { '2502223': 'undefined[object Object]' },
  { '2502627': 'undefined[object Object]' },
  { '2503022': 'undefined[object Object][object Object]' },
  { '2503169': 'undefined[object Object]' }
]

Expected result would be something like:

['2499321': [{
    item_id: 'adsfsdf',
    line_no: 8,
    uom: 'EA',
    qty: 0,
    req_date: 2021-06-07T00:00:00.000Z,
    tracking: 'asdfsad',
    carrier_name: 'UPS Ground',
    carrier_address: 'asdf'
  },{
    item_id: 'asdfasdf',
    line_no: 9,
    uom: 'EA',
    qty: 2,
    req_date: 2021-06-07T00:00:00.000Z,
    tracking: 'asdf',
    carrier_name: 'UPS Ground',
    carrier_address: 'asdfasdf'
  }]


//Then next order_no with objects as nested array

I am not sure why it shows the "undefined" and how do I expand the object? Is this the correct way of achieving this result?

All help is appreciated.

Thank you.