Path: csiph.com!usenet.pasdenom.info!weretis.net!feeder4.news.weretis.net!news.teledata-fn.de!newsfeed.arcor.de!newsspool3.arcor-online.net!news.arcor.de.POSTED!not-for-mail
Content-Type: text/plain; charset="UTF-8"
Message-ID: <67583587.7BbXikoxoM@PointedEars.de>
From: Thomas 'PointedEars' Lahn <PointedEars@web.de>
Reply-To: Thomas 'PointedEars' Lahn <cljs@PointedEars.de>
Organization: PointedEars Software (PES)
Date: Wed, 24 Oct 2012 02:15:24 +0100
User-Agent: KNode/4.4.11
Content-Transfer-Encoding: 8Bit
X-Face: %i>XG-yXR'\"2P/C_aO%~;2o~?g0pPKmbOw^=NT`tprDEf++D.m7"}HW6.#=U:?2GGctkL,f89@H46O$ASoW&?s}.k+&.<b';Md8`dH6iqhT)6C^.Px|[=M@7=Ik[_w<%n1Up"LPQNu2m8|L!/3iby{-]A+#YE}Kl{Cw$\U!kD%K}\2jz"QQP6Uqr],./"?;=4v
Face: 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
Subject: Re: Built-in native method
Newsgroups: comp.lang.javascript
References: <k5sbuj$bt8$1@speranza.aioe.org>
Followup-To: comp.lang.javascript
MIME-Version: 1.0
Lines: 133
NNTP-Posting-Date: 24 Oct 2012 03:15:24 CEST
NNTP-Posting-Host: f0afe0e5.newsspool3.arcor-online.net
X-Trace: DXC=fVL4na]Y3:?_A0jCfgHO6>McF=Q^Z^V384Fo<]lROoR18kF<OcfhCO;?F<P;FJ26_2DZm8W4\YJN<J`:FmdeL>K0JjkNj3FBJ;9E<9gJZ32R\1
X-Complaints-To: usenet-abuse@arcor.de
Xref: csiph.com comp.lang.javascript:16829

Cezary Tomczyk wrote:

> I have read this article:
> http://perfectionkills.com/extending-built-in-native-objects-evil-or-not/
> 
> At the end there is:
> 
> "[...] It should be now clear that extending native built-ins is
> definitely not as risky as messing with host objects. Do it carefully,
> follow spec closely, and use your reasonable judgement.[...]"
> 
> In my project I use some of the 3-rd party library. I didn't knew that
> this library overwritten many of built-in native methods.

Do not use that library then; it is junk.  A library should only overwrite 
built-in methods (that is, the properties that refer to the respective 
Function objects) when they do _not_ exist, or are not as capable as 
required (if it is reasonable to use this and no other method).  Built-in 
methods are inevitably faster than user-defined ones because in most of the 
cases the former are already compiled.

Any library that provides an emulation of a built-in method should only do 
that after it has been determined that the built-in method is unavailable:

  if (typeof foo.whatever != "function")
  {
    foo.whatever = function (…) {
      …
    };
  }

or even

  if (typeof foo.whatever != "undefined")
  {
    foo.whatever = function (…) {
      …
    };
  }

`foo' should not refer to a host object then.  And whenever a built-in 
method is overwritten by a library, it should be done so that the specified 
way of calling that method is still supported.

For example, it has been reasonable (but may be considered obsolete now) to 
overwrite a not-as-capable Math.max() method:

  /**
   * Returns the numeric maximum of all arguments.
   * 
   * @params : Number
   * @return {Number}
   *   <code>-Infinity</code> if no arguments have been passed.
   */
  function Math_max ()
  {
    var result = Number.NEGATIVE_INFINITY;

    /* NOTE: Array.prototype.slice() was not specified before ES 3 */
    for (var i = arguments.length; i--;)
    {
      var arg = parseFloat(arguments[i]);
      if (arg > result)
      {
        result = arg;
      }
    }

    return result;
  }

  var x;

  if (typeof Math.max == "function")
  {
    x = Math.max(1, 2, 3);
  }

  if (typeof x == "undefined" || x != 3)
  {
    Math.max = Math_max;
  }

> And even worst, they work different than they should. I mean, results is
> not the same as expected.
> 
> So, when I'm doing:
> 
> if (String.prototype.trim)
> 
> and its passed then this means that trim method exists.

No, it means that the String prototype object has a `trim' property whose 
value can be type-converted to `true'.

> Is there a way to check if (for example: String.prototype.trim) is a
> real built-in method?

No (looking for "[native code]" is _not_ reliable; function serialization is 
*implementation-dependent*), and there should not be a need for it.  
However, you can increase the probabililty that the property (value) is 
callable, and you can handle odd cases (this may be part of a user-defined 
wrapper):

  if (typeof bar.trim == "function")
  {
    try
    {
      var foo = bar.trim();
    }
    catch (e)
    {
      …
    }
  }

try-catch might need to be guarded for a maximum of backwards-compatibility:

  if (typeof bar.trim == "function")
  {
    eval("try { var foo = bar.trim(); }"
       + "catch (e) { … }");
  }

See also: http://PointedEars.de/es-matrix>


PointedEars
-- 
> If you get a bunch of authors […] that state the same "best practices"
> in any programming language, then you can bet who is wrong or right...
Not with javascript. Nonsense propagates like wildfire in this field.
  -- Richard Cornford, comp.lang.javascript, 2011-11-14