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From: Thomas 'PointedEars' Lahn <PointedEars@web.de>
Newsgroups: comp.lang.javascript
Subject: Re: Object equals other object
Date: Tue, 17 Sep 2019 00:53:28 +0200
Organization: PointedEars Software (PES)
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Xref: csiph.com comp.lang.javascript:37280

Andrew Poulos wrote:

> If I have
> 
> let a = { "c": 1 },
>      b = { "c": 1 };
> 
> then
> 
> console.log(a === b); // false.
> 
> My question is, why was it decided that JavaScript is to return false
> even if the two objects have the same number of properties, all the
> properties are named the same, and all the properties values are
> identical?

History suggests that Brendan Eich decided to define it so for his language 
because Java works this way.  See also my Bachelor thesis 
(<https://10.13140/RG.2.2.25521.63840>), subsection 2.1 “ECMAScript”, and 
references.

Presumably Java, among other programming languages, defined it so because it 
is easier and more efficient to compare two references to one object each 
than to compare all properties of those objects.  Because then you only have 
to compare two pointer values.

Note that in order for two objects to be equal in all properties, not only 
the properties of the object has to be compared, but also the properties of 
their superclasses (in ECMAScript: objects in their prototype chain), i.e. 
the memory areas where the data of the objects are stored and the memory 
areas where the data of their superclasses are stored.

Java has the equals() method to facilitate the customizable comparison of 
objects based on their properties.  Unlike ECMAScript, this requirement also 
extends to strings:

  "foo" == "foo"

yields `false' in Java, while

  "foo".equals("foo")

yields true.  This is actually useful because it also handled Unicode 
composition.  In ECMAScript we usually get away with `==' because we 
consider only ASCII characters; semantically, "e" + "\u0300" == "è" should 
yield `true' but does not, and to date there is apparently no method defined 
in ECMAScript to do a proper comparison; String.prototype.localeCompare(), 
ECMA-402, §14.1.1 just ignores the accent, it does not actually compare
the composed/decomposed sequences.

<https://stackoverflow.com/a/7520464/855543>
<https://stackoverflow.com/a/56574119/855543>
<https://docs.oracle.com/javase/9/docs/api/java/lang/String.html>

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