Re: Object.defineProperties

From	Thomas 'PointedEars' Lahn <PointedEars@web.de>
Newsgroups	comp.lang.javascript
Subject	Re: Object.defineProperties
Date	2017-05-06 16:43 +0200
Organization	PointedEars Software (PES)
Message-ID	<2032926.ElGaqSPkdT@PointedEars.de> (permalink)
References	(2 earlier) <oec3h1$2dav$1@csiph.com> <1943190.NgBsaNRSFp@PointedEars.de> <oeid9d$1ag1$1@csiph.com> <1592229.TLkxdtWsSY@PointedEars.de> <oekitc$2tgv$1@csiph.com>

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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:
>>> [...]
>>>>> 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();
>>   }
> 
> 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”.
 
>>>>> 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.
 
> 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.

>              return false;
>          }
> 
>          objectType = typeof obj;

IMO, DRY demands declaration and initialization in one statement, if 
possible.
 
>          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.

>          ) {
>              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.
 
-- 
PointedEars
FAQ: <http://PointedEars.de/faq> | <http://PointedEars.de/es-matrix>
<https://github.com/PointedEars> | <http://PointedEars.de/wsvn/>
Twitter: @PointedEars2 | Please do not cc me./Bitte keine Kopien per E-Mail.

Thread

Object.defineProperties Cezary Tomczyk <cezary.tomczyk@gmail.com> - 2017-05-03 08:36 +0200
  Re: Object.defineProperties Cezary Tomczyk <cezary.tomczyk@gmail.com> - 2017-05-03 10:14 +0200
    Re: Object.defineProperties Cezary Tomczyk <cezary.tomczyk@gmail.com> - 2017-05-03 10:59 +0200
      Re: Object.defineProperties Cezary Tomczyk <cezary.tomczyk@gmail.com> - 2017-05-03 12:36 +0200
        Re: Object.defineProperties Cezary Tomczyk <cezary.tomczyk@gmail.com> - 2017-05-03 18:47 +0200
          Re: Object.defineProperties Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2017-05-05 18:18 +0200
    Re: Object.defineProperties Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2017-05-05 18:14 +0200
      Re: Object.defineProperties Cezary Tomczyk <cezary.tomczyk@gmail.com> - 2017-05-05 19:37 +0200
        Re: Object.defineProperties Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2017-05-05 20:11 +0200
          Re: Object.defineProperties Cezary Tomczyk <cezary.tomczyk@gmail.com> - 2017-05-06 15:26 +0200
            Re: Object.defineProperties Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2017-05-06 16:43 +0200
              Re: Object.defineProperties Cezary Tomczyk <cezary.tomczyk@gmail.com> - 2017-05-06 20:23 +0200
                Re: Object.defineProperties Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2017-05-06 22:21 +0200
                Re: Object.defineProperties Cezary Tomczyk <cezary.tomczyk@gmail.com> - 2017-05-06 23:19 +0200
                Re: Object.defineProperties Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2017-05-07 02:40 +0200
            Re: Object.defineProperties Stefan Weiss <krewecherl@gmail.com> - 2017-05-06 22:37 +0200
              Re: Object.defineProperties Cezary Tomczyk <cezary.tomczyk@gmail.com> - 2017-05-06 23:05 +0200
                Re: Object.defineProperties Stefan Weiss <krewecherl@gmail.com> - 2017-05-07 00:29 +0200
                Re: Object.defineProperties Cezary Tomczyk <cezary.tomczyk@gmail.com> - 2017-05-07 10:06 +0200
                Re: Object.defineProperties Stefan Weiss <krewecherl@gmail.com> - 2017-05-08 00:50 +0200
                Re: Object.defineProperties Cezary Tomczyk <cezary.tomczyk@gmail.com> - 2017-05-08 13:17 +0200
                Re: Object.defineProperties Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2017-05-07 02:37 +0200
                Re: Object.defineProperties Cezary Tomczyk <cezary.tomczyk@gmail.com> - 2017-05-07 09:42 +0200
                Re: Object.defineProperties Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2017-05-07 17:11 +0200
                Re: Object.defineProperties Cezary Tomczyk <cezary.tomczyk@gmail.com> - 2017-05-07 20:08 +0200
        Re: Object.defineProperties Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2017-05-05 20:59 +0200
          Re: Object.defineProperties John G Harris <niam@jghnorth.org.uk.invalid> - 2017-05-06 10:35 +0100
  Re: Object.defineProperties Cezary Tomczyk <cezary.tomczyk@gmail.com> - 2017-05-05 08:32 +0200
  Re: Object.defineProperties Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2017-05-05 18:24 +0200

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