Is object changes immutably?

Question

I'm trying to flatten and deep copy of an object.

Here's an example of how I try to do:

const data = {
  firstObj: {
    data: 'Hi!',
    nestedArrayOfObject: [{
      name: 'hey',
      property: 'object'
    }],
  },
  secondObj: {
    name: 'second',
    nestedArray: []
  },
}

const object = {}
const keys = Object.keys(data)

for (let i = 0; i < keys.length; i += 1) {
  const items = Object.keys(data[keys[i]])

  for (let j = 0; j < items.length; j += 1) {
    object[items[j]] = data[keys[i]][items[j]]
  }
}

console.log(object)

As I understand, nested objects are being only linked to the new object, but not cloned.

How to do it correctly without additional libraries?

Are you trying to flatten the object or make a deep clone? What do you want the final object to look like? — Mark, Apr 13 '19 at 04:59
If you want to flatten it, how will you deal with duplicate keys like `name`? — Mark, Apr 13 '19 at 05:04
@MarkMeyer I mean flatten only on two levels. The code in an example is doing it but by my knowledge, it not does it immutably to 3 level objects. — Andrey Osiyuk, Apr 13 '19 at 05:09

score 1 · Accepted Answer · answered Apr 13 '19 at 05:00

1

You can use JSON.parse(JSON.stringify(obj)) to make a deep clone

const data = {
  firstObj: {
    data: 'Hi!',
    nestedArrayOfObject: [{
      name: 'hey',
      property: 'object'
    }],
  },
  secondObj: {
    name: 'second',
    nestedArray: []
  },
}

const object = {}
const keys = Object.keys(data)

for (let i = 0; i < keys.length; i += 1) {
  const items = Object.keys(data[keys[i]])

  for (let j = 0; j < items.length; j += 1) {
    object[items[j]] = JSON.parse(JSON.stringify(data[keys[i]][items[j]]))
  }
}

console.log(object)

answered Apr 13 '19 at 05:00

Code Maniac

37,143
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Wow! Didn't know that way. Is it a performance friendly way? – Andrey Osiyuk Apr 13 '19 at 05:11
You can read more [here](https://stackoverflow.com/questions/20662319/javascript-deep-copy-using-json) and also read the linked answer too – Code Maniac Apr 13 '19 at 05:18
1

@chrisands does have limitations though...for example Date objects or functions – charlietfl Apr 13 '19 at 05:21

score 0 · Answer 2 · answered Apr 13 '19 at 04:55

0

let new_object = Object.assign({}, your_object);

answered Apr 13 '19 at 04:55

Ezequiel Fernandez

954
11
18

1

Your answer came in lower quality posts. Please provide some explanation even though your code is self explanatory. – Harsha Biyani Apr 13 '19 at 05:36

Jack Bashford · Answer 3 · 2019-04-13T05:04:11.020

0

Use Object.assign:

const data = {
  firstObj: {
    data: 'Hi!',
    nestedArrayOfObject: [{
      name: 'hey',
      property: 'object'
    }],
  },
  secondObj: {
    name: 'second',
    nestedArray: []
  },
};
const object = Object.assign({}, data.firstObj, data.secondObj);

console.log(object);

Alternatively, use the spreading behaviour ... introduced in ECMAScript 6:

const data = {
  firstObj: {
    data: 'Hi!',
    nestedArrayOfObject: [{
      name: 'hey',
      property: 'object'
    }],
  },
  secondObj: {
    name: 'second',
    nestedArray: []
  },
};
const object = { ...data.firstObj, ...data.secondObj };

console.log(object);

edited Apr 13 '19 at 05:04

answered Apr 13 '19 at 05:01

Jack Bashford

43,180
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Your `Object.assign()` targets the original object property – User863 Apr 13 '19 at 05:03
Whoops, my bad @AswinKumar. – Jack Bashford Apr 13 '19 at 05:04

Is object changes immutably?

3 Answers3