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From: Thomas 'PointedEars' Lahn <PointedEars@web.de>
Newsgroups: comp.lang.javascript
Subject: Re: Why JavaScript 'seems' to get addition wrong
Date: Sat, 03 Oct 2015 05:24:28 +0200
Organization: PointedEars Software (PES)
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Ben Bacarisse wrote:

> AbdulFattah Popoola <abdulapopoola@gmail.com> writes:
>> One of the most popular gotchas of JavaScript is its behaviour when
>> adding operands. For example, the output of {} + 2 is different from 2
>> + {}.
> 
> That's not an example of addition.  I think it's better to say that one
> of the gochas of EcmaScript is that + means more than one thing.

If it were another programming language, you might just say that the 
operator “+” is overloaded: it does either addition or string concatenation 
in ECMAScript, depending on the type of its operands:

  window.alert(Array(16).join("wat" - 1) + " Batman!");

(Shamelessly stolen from <https://www.destroyallsoftware.com/talks/wat> when 
it was still working ;-))

Unfortunately, with few exceptions (the toString() and valueOf() methods of 
objects), in general one cannot define (this) operator overloading in 
ECMAScript.  (It would be easy if they [ECMA TC39] specified it the Python 
way, with Specification algorithms supporting __add__(), __sub__(), etc. 
methods on objects. [1]  Some of that is now even specified in ECMAScript 
2015, with Proxy [2a], and you can make use of that since quite a while 
[2b].)  But one can implement operators as methods, and call methods instead 
of using operators.  I have done that in the math library of JSX [3].
 
>> I explained why the puzzling results occur in this post:
>> http://abdulapopoola.com/2015/09/30/why-javascript-seems-to-get-addition-wrong/.
>>
>> Please do share your feedback.
> 
> Share you explanation here, and I'll share my feedback here.

They are posting via Google Groups; you can be quite certain that they do 
not even know what “here” (Usenet) actually is.
 
__________
[1] 
<https://docs.python.org/3/reference/datamodel.html?highlight=__add__#emulating-callable-objects> pp.
[2a] <https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Proxy> p.
[2b] <http://pointedears.de/wsvn/JSX/trunk/array.js> (jsx.array.Array and 
     jsx.array.BigArray)
[3] <http://PointedEars.de/wsvn/JSX/trunk/math.js>
    <http://PointedEars.de/wsvn/JSX/trunk/math/>
-- 
PointedEars
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