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: Sat, 6 May 2017 15:26:03 +0200
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In-Reply-To: <1592229.TLkxdtWsSY@PointedEars.de>
Xref: csiph.com comp.lang.javascript:33235

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. :-)

>>>> 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() :)

Finally I rewrote it a bit:

     var _toString = {}.toString;

     function isTypeOf(obj, typeToCheck) {
         var objectType;

         if (arguments.length !== 2) {
             return false;
         }

         objectType = typeof obj;

         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'
         ) {
             return true;
         }

         return _toString.call(obj).slice(8, -1).toLowerCase() === 
typeToCheck.toLowerCase();
     }

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