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From: Thomas 'PointedEars' Lahn <PointedEars@web.de>
Newsgroups: comp.lang.javascript
Subject: Re: Object.defineProperties
Date: Fri, 05 May 2017 18:14:59 +0200
Organization: PointedEars Software (PES)
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References: <oebtq0$2611$1@csiph.com> <objects-20170503082342@ram.dialup.fu-berlin.de> <oec3h1$2dav$1@csiph.com>
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Cezary Tomczyk wrote:

> On 03/05/2017 09:24, Stefan Ram wrote:
>> Cezary Tomczyk <cezary.tomczyk@gmail.com> writes:
>>> Native built-in Object.defineProperties method allows me to add
>>> properties to a function as the function is an object.
>>
>>   The Web gives:
>>
>> function isObject(val) {
>>     if (val === null) { return false;}
>>     return ( (typeof val === 'function') || (typeof val === 'object') );
>> }
>>
>>   . The above might not work with host objects, which might
>>   have even other types.

Correct.  But it SHOULD work with newer implementations, see 

<http://www.ecma-international.org/ecma-262/7.0/#sec-typeof-operator>

    [This *huge* specification has a content filter in the sidebar (now?),
     which is very handy.  It would be better, though, if it were not *only*
     one huge document.]

>>   So another suggestion from the Web is:
>>
>> function isObject(obj) {
>>   return obj === Object(obj);
>> }

Nice.  But note that this would also designate convertible primitive values 
“not an object”: isObject(42) === false.

>>   Other observations:
>>
>>   Object.getPrototypeOf does /not/ throw when called with an object.

I beg your pardon?
 
> I use:
> 
>      function isTypeOf(obj, typeToCheck) {
>          if (arguments.length < 2) {
>              return false;
>          }
>          return Object.prototype.toString.call(obj).slice(8,
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> -1).toLowerCase() === typeToCheck.toLowerCase();
  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>      }
> 
> which gives me more precisely a type of object.

I hope you have optimized that somewhat.

> The Object.defineProperties says about object, but function, array are
> also objects. That's why:
> 
>    if (typeof obj !== 'object' || obj === null)
>      throw new TypeError('bad obj');
> 
> looks like a bug to me.

typeof [] === "object", so that is OK.  (common misconception)

typeof function () {} === "function", so that is not OK in theory; however, 
one might decide that it is not OK to modify function objects.
 
-- 
PointedEars
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