Ecma6, Object.assign doesn't do a deep copy

Question

dst = { "a" : 1}
src = { "edf" : {"zyx" : "right"}}
Object.assign(dst, src)
src.edf.zyx = "wrong"
console.log(dst["edf"]["zyx"])

I expect to see 'right' as the output but it prints 'wrong'.

It means, Object.assign has not done a deep copy of complex objects from source to destination. How can i do deep copy?

Note: i am aware of lodash.deepClone, but i am trying to avoid outside frameworks

Yeah, `Object.assign()` only performs shallow merging of properties. But, there isn't currently a built-in function for deep merging, recursively discovering properties in nested objects. — Jonathan Lonowski, Nov 19 '15 at 06:38
you can use JSON, but that can be slow-ish for large data sets. still, it's as close to a built-in clone as possible and is actually faster than most library methods. — dandavis, Nov 19 '15 at 06:39
To note, parsing to and from JSON will not work for functions. — Travis J, Nov 19 '15 at 06:41
Sadly, it's not supposed to return a deep copy. http://www.ecma-international.org/ecma-262/6.0/#sec-object.assign — Brent Barbata, Nov 19 '15 at 06:53
let dst = JSON.parse(JSON.stringify(src)); see: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/assign — Manohar Reddy Poreddy, Dec 12 '17 at 06:28
@JonathanLonowski what about `var newObj = eval(oldObj.toSource())` for es5 and `var newO={...old}` for es6? — B''H Bi'ezras -- Boruch Hashem, Jun 03 '20 at 01:22

score 0 · Answer 1 · edited Oct 02 '18 at 10:08

0

First I want to tell you that it's not bulletproof solution (in case of date object). If you want "right" as answer, here is your solution:

var dst,src = { "edf" : {"zyx" : "right"} };
dst = JSON.parse(JSON.stringify(src));
dst["a"] = 1;
src.edf.zyx = "wrong";
console.log(src, dst);

So please read these links to understand deep copy better

edited Oct 02 '18 at 10:08

shaedrich

answered Nov 19 '15 at 07:15

Rajan Singh

1

Try running this on my above example obj to see where it fails (specifically, date and function). – Brent Barbata Nov 19 '15 at 07:40
It will fail definitely that's why I have given the links & also mentioned 'If you want "right" as answer'. – Rajan Singh Nov 19 '15 at 08:38
1

Note that this does not copy over non-enumerable properties or symbols, so this is not bullet-proof. – Sheepy Nov 19 '15 at 08:41

1 Answers1