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From: Cezary Tomczyk <cezary.tomczyk@gmail.com>
Newsgroups: comp.lang.javascript
Subject: Re: Object.defineProperties
Date: Sat, 6 May 2017 20:23:06 +0200
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References: <oebtq0$2611$1@csiph.com> <objects-20170503082342@ram.dialup.fu-berlin.de> <oec3h1$2dav$1@csiph.com> <1943190.NgBsaNRSFp@PointedEars.de> <oeid9d$1ag1$1@csiph.com> <1592229.TLkxdtWsSY@PointedEars.de> <oekitc$2tgv$1@csiph.com> <2032926.ElGaqSPkdT@PointedEars.de>
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Xref: csiph.com comp.lang.javascript:33239

On 06/05/2017 16:43, Thomas 'PointedEars' Lahn wrote:
> Cezary Tomczyk wrote:
>
>> On 05/05/2017 20:11, Thomas 'PointedEars' Lahn wrote:
>>> Cezary Tomczyk wrote:
>>>> On 05/05/2017 18:14, Thomas 'PointedEars' Lahn wrote:
>>>>> Cezary Tomczyk wrote:
>>>> [...]
[...]
>>> 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();
>>>   }
>>
>> Tiny optimisation, but that's fine. :-)
>
> Tiny optimization with big impact, I think.  It saves
>
>   - 1 lookup along the scope chain up to the global object for “Object”
>     *every time the function is called*
>
>   - 2 lookups along the prototype chain each for “prototype” and “toString”
>     *every time the function is called*
>
> and removes the dependency on a potentially non-initial value of
> “Object.prototype” and “Object.prototype.toString”.

That's true, but it is also important to mention that the impact is 
significant in case of hundred operations at the same time.

>>>>>> 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” ;-)).
>>
>> Ah, right, I forgot about Array.isArray() :)
>
> Be sure to emulate it if it is not there.

Yes, thanks.

>> Finally I rewrote it a bit:
>>
>>      var _toString = {}.toString;
>>
>>      function isTypeOf(obj, typeToCheck) {
>>          var objectType;
>>
>>          if (arguments.length !== 2) {
>
> This change does not make sense to me.  “< 2” was clearer.

Passing 1 argument doesn't make sense and that's why I've used !== 2.

>>              return false;
>>          }
>>
>>          objectType = typeof obj;
>
> IMO, DRY demands declaration and initialization in one statement, if
> possible.

I did it on purpose. If argument will be !== 2 then it is not efficient 
to initialize anything before.

>>          if (typeToCheck === 'array' && Array.isArray(obj)
>>              || typeToCheck === 'null' && objectType === 'object'
>>              || typeToCheck === 'object' && objectType === 'object'
>>              || typeToCheck === 'number' && objectType === 'number'
>>              || typeToCheck === 'string' && objectType === 'string'
>>              || typeToCheck === 'boolean' && objectType === 'boolean'
>>              || typeToCheck === 'undefined' && objectType === 'undefined'
>>              || typeToCheck === 'symbol' && objectType === 'symbol'
>
> I would use parentheses to make clear what conditions belong together.

That can be done :-)

>>          ) {
>>              return true;
>>          }
>>
>>          return _toString.call(obj).slice(8, -1).toLowerCase() ===
>> typeToCheck.toLowerCase();
>>      }
>
> The question remains: What is being *gained* by this comparably inefficient
> precision instead of duck typing?  _Not_ all things that *can* be done also
> *should* be done.

The gain is to get the real type (let me call it like that) of object.

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