Efficient Deep copy in NodeJS

Question

I want to deep copy an array of integers in NodeJS. The first method I tried is

obj2 = JSON.parse(JSON.stringify(obj1));

However, it is so slow because it is a big array.

Now I am using

var l = obj1.length;
while (l--){
  obj2.push(obj1[l]);
}

Though it is much faster, I am wondering if there exist better solutions? Thank you all!

What exactly does a "deep copy" of a simple array of integers mean? What would be the difference from a shallow copy ? — adeneo, Apr 25 '16 at 21:31
@adneo. I need use two different array (original order and sorted) — Luyao Wang, Apr 25 '16 at 21:37
because I need some information of the original position of the original array later... — Luyao Wang, Apr 25 '16 at 21:42
In 2023, use `structuredClone` : https://stackoverflow.com/questions/122102/what-is-the-most-efficient-way-to-deep-clone-an-object-in-javascript/122704#122704 — Nico Toub, Feb 24 '23 at 06:19

adeneo · Accepted Answer · 2016-04-25T22:16:29.453

2

If it's an array, did you try just

var arr2 = arr1.slice(0);

It does create a shallow copy, but for an array containing just primitive integers it shouldn't matter.

edited Apr 25 '16 at 22:16

answered Apr 25 '16 at 21:30

adeneo

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Arguments of slice are [optional](https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Array/slice), so `arr1.slice()` would do just fine. – Роман Парадеев Apr 25 '16 at 21:38
@РоманПарадеев - and still I decided to add `0` as an argument, to make it clear that we're slicing from the beginning. – adeneo Apr 25 '16 at 21:39
Why not explicitly set both indices then? – Роман Парадеев Apr 25 '16 at 21:42
@РоманПарадеев - because according to the [documentation](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/slice) the first argument isn't optional, only the second one is. – adeneo Apr 25 '16 at 21:45
@adeneo you show docs for **string**, for an array the first argument is [optional](https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Array/slice) – isvforall Apr 25 '16 at 21:46
@isvforall - yeah, thought I was clever there and noone would notice, but both arguments are optional. Most of the time though you'll see `slice(0)` for arrays, probably because it's so common to add the zero whenever you use `slice()` as it's needed for strings, and I always add it without even thinking about it. It doesn't really matter, if you leave it out, the engine will just insert a zero for you, same thing as writing yourself. – adeneo Apr 25 '16 at 22:15
Question clearly states "deep copy" – Michal M. Jan 24 '23 at 11:39

score 1 · Answer 2 · answered Apr 25 '16 at 21:33

1

you can also make it like

var arr = [1,2,3,4,5,6,7,8],
    brr = arr.map(e => e);

answered Apr 25 '16 at 21:33

Redu

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score 0 · Answer 3 · answered Apr 25 '16 at 21:36

0

If your array contains numbers only (it won't to work if your array contains arrays), you could use Array.prototype.slice function without arguments

var arr1 = [1, 2, 3, 4, 5];
var arr2 = arr1.slice();

answered Apr 25 '16 at 21:36

isvforall

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score 0 · Answer 4 · answered Apr 25 '16 at 21:58

If you need to get a sorted array and save the information on the position of the element in the original array:

0) The original array:

var obj1 = [1, 2, 3, 100, 5, 0, 200, 30];

1) It is necessary to keep the original position:

var index = Object.keys( obj1 ).sort( function(a, b) {
  return obj1[a] - obj1[b];
});

// >> ["5", "0", "1", "2", "4", "7", "3", "6"]

2) Get a sorted array:

var obj2 = obj1.sort( function(a, b) {
  return a-b;
});

// >> [0, 1, 2, 3, 5, 30, 100, 200]

3) Find the original position of the element with new index '0':

var originalIndex = index[0];

// >> "5"

Efficient Deep copy in NodeJS

4 Answers4