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From: Thomas 'PointedEars' Lahn <PointedEars@web.de>
Newsgroups: comp.lang.javascript
Subject: Re: Object.defineProperties
Date: Fri, 05 May 2017 20:11:54 +0200
Organization: PointedEars Software (PES)
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Cezary Tomczyk wrote:

> On 05/05/2017 18:14, Thomas 'PointedEars' Lahn wrote:
>> Cezary Tomczyk wrote:
> [...]
>>> 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.
> 
> I can't find a reliable way at the moment. Perhaps I should combine few
> methods, but that might be an overengineering.

To begin with, you should have

  var _toString = {}.toString;

  function isTypeOf(obj, typeToCheck) {
    if (arguments.length < 2) {
      return false;
    }
    return _toString.call(obj).slice(8, -1).toLowerCase() === 
typeToCheck.toLowerCase();
  }
 
>>> 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)
> 
> In a sense of that [] is an object - yes, but I'd prefer to know that
> tested object is in fact an Array type. Operator instanceof looks
> promising, but I need to check it anyway.

Array.isArray() exists (since ECMAScript Ed. 5).  For general and own 
(array) types, I am using “instanceof” or “constructor”.  Most of the time, 
though, duck typing instead (“quack” ;-)).
 
>> typeof function () {} === "function", so that is not OK in theory;
>> however, one might decide that it is not OK to modify function objects.
> 
> Functions are objects so they can be extended like any other objects.

They also have built-in, non-inherited, read-only properties.  I augment 
function objects only as a last resort (currently, to tag them as user-
defined).
 
-- 
PointedEars
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