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Message-ID: <3504411.n7x7zaDXQ0@PointedEars.de>
From: Thomas 'PointedEars' Lahn <PointedEars@web.de>
Reply-To: Thomas 'PointedEars' Lahn <cljs@PointedEars.de>
Organization: PointedEars Software (PES)
Date: Wed, 12 Mar 2014 15:34:20 +0100
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Subject: Re: class needs to initialize vars, set data structure
Newsgroups: comp.lang.javascript
References: <972c7156-b68b-4ff4-8d82-55f00676b1a7@googlegroups.com> <return-20140312004838@ram.dialup.fu-berlin.de> <set-20140312005707@ram.dialup.fu-berlin.de> <set-20140312142217@ram.dialup.fu-berlin.de>
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Xref: csiph.com comp.lang.javascript:23570

Stefan Ram wrote:

> ram@zedat.fu-berlin.de (Stefan Ram) writes:
>> function Set(){ this.map = {}; }
> 
>   Next version:
>  
> function Set(){ this.map = Object.create( null ); };

This makes the “map” property public, allowing everyone to mess with the 
set.  It also requires an implementation of ECMAScript Edition 5 or later, 
or an emulation of Object.create().

> Set.prototype =
> { add      : function( element ){ this.map[ element ]= true; } ,
>   remove   : function( element ){ delete this.map[ element ]; },
>   contains : function( element ){ return element in this.map; },

Again, these work reliably only for String values where the value is not the 
name of a *non-inherited* built-in property, or for non-String values where 
the string representation of the value is no such name.

>   count    : function( element ){ return Object.keys( this.map ).length;
>   }};

This would prevent the methods from being created on each invocation of 
Set(), however it overwrites the existing “prototype” property so that the 
“constructor” property of the object referred to from the “prototype” 
property value refers to the same object as “Object”, not as “Set” (because 
it now refers to an Object instance).  It also allows everyone to mess with 
the methods because they are public.

Instead of bothering everyone with your repetitions of common mistakes, you 
should read previous discussions before you post, and follow-ups to your 
postings more carefully.  And RTFM, RTFFAQ, STFW.

-- 
PointedEars
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