Path: csiph.com!.POSTED.204-73-239-109.cust.centrio.cz!not-for-mail
From: Cezary Tomczyk <cezary.tomczyk@gmail.com>
Newsgroups: comp.lang.javascript
Subject: Re: Object.defineProperties
Date: Wed, 3 May 2017 12:36:12 +0200
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On 03/05/2017 11:24, Stefan Ram wrote:
> Cezary Tomczyk <cezary.tomczyk@gmail.com> writes:
>> And they are all passing.
>
>   Yes, but the OP question was about detecting
>   whether something is an /object/.

To be precise I was asking rather about why polyfill of 
Object.defineProperties

https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Object/defineProperties#Polyfill

doesn't allow

   if (typeof obj !== 'object' || obj === null)
     throw new TypeError('bad obj');

to add properties to the other objects like function or array. :-)

The native built-in Object.defineProperties does allow it.

>   And, my previous example was not to the point!
>   This is more like it:
>
> let a = new String( "abc" );
>
> console.log( Object.prototype.toString.call( a ) );
>
> Object.defineProperty
> ( a, Symbol.toStringTag, { get: function() { return "Number"; }});
>
> console.log( Object.prototype.toString.call( a ) );
>
>   This will print
>
> [object String]
> [object Number]
>
>   even though ťaŤ is still a string. Console:
>
>> a
> < String { "abc", 4 more... }

Interesting. I didn't know about Symbol.toStringTag 
(https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol/toStringTag). 


Seems typeof operator returns "object" before changing and after 
changing string description of an object.

So, I can't trust what's returned by 
Object.prototype.toString.call(obj). However, if I want to check what 
type is an object then I can use typeof operator, but it's not quite 
thing I want as the typeof for object type array give me "object".

 From one side it is fine as the array is an object in fact, but what I 
wanted is to check what's the real type of an object. 
Object.prototype.toString.call() gives me what I want, but only under 
condition that the default string description of an object has not changed.

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