Spread operator copies Symbol property from one to another object

[Konrud]

Current implementation of the spread operator in browsers copy Symbol property when used.

What I see here is inconsistency.
On the one hand spread operator and Object.assign both do copy Symbol property.
On the other hand, Symbol property doesn't appear in for...in loop and completely ignored by JSON.stringify and JSON.parse.

Steps to reproduce the problem:

1. Define object on which Symbol will be used as property name (e.g. obj[Symbol("secret property")] = "secret value")
2. Using spread operator copy all properties to another object (e.g. const newObj = {...obj})

Spread operator should copy only own enumerable (which is not relevant to the property named using Symbol as it's not enumerable) properties from a provided object onto a new object.

Checked in:
Chrome version: 63.0.3239.132
(Windows 7)

working example: https://goo.gl/SkHd3H

[loganfsmyth]

Spread operator should copy only own enumerable

That is exactly what it is doing.

(which is not relevant to the property named using Symbol as it's not enumerable)

That is not the case, Symbol properties may or may not be enumerable, just like any other property.

On the other hand, Symbol property doesn't appear in for...in loop and completely ignored by JSON.stringify and JSON.parse.

What is leading to your confusion is that for..in and JSON.stringify (and Object.keys and such) don't simply iterate own enumerable properties, it is explicitly specced to iterate and only process string-keyed properties of the given object.

[gabssnake]

This seems completely rational, yet in practice, kinda sucks anyway

[LinusU]

yet in practice, kinda sucks anyway

Why? I think it would be more weird if it didn't copy symbols? 🤔

[gabssnake]

@LinusU well, if you're using plain objects as dictionaries, you'd only want stringy-key entries. I'd argue that this is a very common use case.

[LinusU]

Well, if you do that, then they wouldn't have any symbols on them that would get copied over? 🤔

Sorry, I'm not trying to argue with you, I'm just trying to understand your use case