How to push response in nested onject

Question

I have a nested data inside which I am trying to push my response I am getting from the server,

My data is :

let d = [{
    "dashId": 3,
    "dashName": "one",
    "dashData": []
  },
  {
    "dashId": 4,
    "dashName": "two",
    "dashData": [{
      "nestedId": 1,
      "nestedData": "how are you"
    }]
  }
]

This the data below I want to push

let res = [{
  "nestedId": 11,
  "nestedData": "I am fine"
}]

What I am doing is:-

let dd = d.map(li => {
  if (li.dashId === 3) {
    li.dashData.push(res)
  }
})

console.log(dd)

I am getting output as undefined

[ undefined, undefined ]

You should be returning from the map callback to specify what you want to map the current element to. You're not returning anything so you'll get undefined. Instead, you're changing your original `d` array's objects - See: [Is performing a mapping operation without using returned value an antipattern?](https://stackoverflow.com/q/56903693) — Nick Parsons, Nov 11 '20 at 13:55
You need to return a value from `map` if you want to get a new array. — , Nov 11 '20 at 13:58
@expressjs123 OI tried returning like ` return li.dashData.push(res)` but it returns `[1, undefined]` — manish thakur, Nov 11 '20 at 14:02

score 3 · Accepted Answer · answered Nov 11 '20 at 13:57

Array.map function creates a new array populated with the results of calling a provided function on every element in the calling array. So the callback inside map should return an item and on your code, nothing is returned on callback.

In your case, it's better to use Array.forEach as follows.

const d = [{
    "dashId": 3,
    "dashName": "one",
    "dashData": []
  },
  {
    "dashId": 4,
    "dashName": "two",
    "dashData": [{
      "nestedId": 1,
      "nestedData": "how are you"
    }]
  }
];

const res = [{
  "nestedId": 11,
  "nestedData": "I am fine"
}];

d.forEach(li => {
  if (li.dashId === 3) {
    li.dashData.push(...res)
  }
});

console.log(d);

score 0 · Answer 2 · answered Nov 11 '20 at 17:38

You just need to return the li in your map callback:

let dd = d.map(li => {
  if (li.dashId === 3) {
    li.dashData.push(res)
  }
  return li
})

I'm not sure what do you need but I think res should not be an array:

const res = {
  "nestedId": 11,
  "nestedData": "I am fine"
};

How to push response in nested onject

2 Answers2