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From: Cezary Tomczyk <cezary.tomczyk@gmail.com>
Newsgroups: comp.lang.javascript
Subject: Re: Cloning an object
Date: Thu, 5 Jul 2018 20:37:55 +0200
Organization: csiph.com Internet News Service
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References: <aYCdnU3Tes0_oLbGnZ2dnUU7-LHNnZ2d@westnet.com.au> <1620852.VI2in3QvqR@PointedEars.de> <d9423a2c-3ca3-7571-6fa0-aca40b1c6d0f@PointedEars.de> <9909bfec-c6e7-2a4a-2a54-ec9f271691c8@PointedEars.de> <phdcst$1hro$1@csiph.com> <4395113.31r3eYUQgx@PointedEars.de> <phkj7m$2ugj$1@csiph.com> <506b67da-b086-3d0e-5985-d0f8214da432@PointedEars.de>
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Xref: csiph.com comp.lang.javascript:35353

On 05/07/2018 19:49, Thomas 'PointedEars' Lahn wrote:
> Cezary Tomczyk wrote:
> 
>> On 04/07/2018 23:25, Thomas 'PointedEars' Lahn wrote:
>>>     function clone (obj, deepCopy)
>>>     {
>>>       const CLONE = Object.create(Object.getPrototypeOf(obj));
>>>
>>>       Object.getOwnPropertyNames(obj).forEach((name) => {
>>>         const DESC = Object.getOwnPropertyDescriptor(obj, name);
>>>
>>>         if (deepCopy)
>>>         {
>>>           /* FIXME: Standardize Object.isObject() */
>>>           if (("value" in DESC)
>>>               && (typeof DESC.value == "object")
>>>               && (DESC.value != null))
>>>           {
>>>             DESC.value = clone(DESC.value);
>>>           }
>>>         }
>>>
>>>         Object.defineProperty(CLONE, name, DESC || {});
>>>       });
>>>
>>>       return CLONE;
>>>     }
>>> […]
>>
>> It passes for simple objects, but if the property has a value as an
>> array or Date object then it doesn't work.
> 
> I agree regarding Date instances, but where is the problem with Array
> instances?

It doesn't create a real Array copy. Try clone following object:

var o = {
   a: 1,
   b: [
     {
       test: 'test'
     }
   ]
};

var cloned = clone(o);

o.b[0].test = 'something';

expect(cloned.b[0].test).toBe('test');

This test doesn't pass. Basically, modifications on original object 
should not modify cloned object.

-- 
Cezary Tomczyk
http://www.ctomczyk.pl/
https://www.aslint.org/