Re: Differences between [[Class]] and constructor

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From	Thomas 'PointedEars' Lahn <PointedEars@web.de>
Newsgroups	comp.lang.javascript
Subject	Re: Differences between [[Class]] and constructor
Date	Tue, 02 Jun 2015 23:05:48 +0200
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Andreas Bergmaier wrote:

> Stefan Ram schrieb:
>>    I have observed that the class ([[Class]]) name and the
>>    constructor name of an object often is the same!
> 
> This might be the case for plain objects with the native constructors.
> It is not for almost every other object, like
> 
>      var p = new (function Person(){});
>      className(p) // "object"

No, with this code it would be a capital “O”.

>      p.constructor // Person
> 
>>    The first difference I found is: You can change the
>>    constructor name, but not the class name.
> 
> Not exactly. You cannot change constructor names either, as the `.name`
> property of functions is typically non-writable (if it exists at all, it
> is non-standard, as opposed to [[Class]]). See
> https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/name
> for more information.
> 
> What you can arbitrarily change is the `.constructor` property of any
> normal object, there are no limitiations here.

Whereas “normal object” would be one whose prototype is not constructed 
using (an emulation of) Object.create(…), as I pointed out in an update of 
my <http://stackoverflow.com/a/12593269/855543> today:

With a conforming implementation of Object.create(), following

  WeatherWidget.prototype =
    Object.create(Widget.prototype, {constructor: {value: WeatherWidget}});

the “constructor” property of WeatherWidget instances is neither writable, 
nor enumerable or configurable.  Of those, an emulation of Object.create() 
can only accomplish read-onlyness, see Function.prototype.extend() in 
JSX:object.js.

-- 
PointedEars
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Re: Differences between [[Class]] and constructor Andreas Bergmaier <andber93@web.de> - 2015-06-02 21:32 +0200
  Re: Differences between [[Class]] and constructor Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-06-02 23:05 +0200

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