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Message-ID: <1476035.p2tWUPlOUs@PointedEars.de>
From: Thomas 'PointedEars' Lahn <PointedEars@web.de>
Reply-To: Thomas 'PointedEars' Lahn <cljs@PointedEars.de>
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Date: Mon, 10 Feb 2014 14:53:33 +0100
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Subject: Re: Cons in the following object implementation
Newsgroups: comp.lang.javascript
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Xref: csiph.com comp.lang.javascript:23053

Alon Melanker wrote:

> On a job interview, I've been asked to defined an object with a private
> variable and getter/setter for this private variable.
> 
> I chose the following:
> 
> var obj = function() {
>    var private;
>    
>    this.setPrivate(val) {
>       private = val;
>    }
>    
>    this.getPrivate() {
>       return private;
>    }
> };
> 
> 
> When I've finished to implement the object the interviewer told me there
> are some problems\cons with this object and those "problems" are not the
> setter/getter functions.
> 
> I've been asked to point out those flaws, but I couldn't.
> 
> Does anyone can point out the flaws in the object?

This program is syntactically in error, which you would have known if you 
had tried to run it before you asked.

If one mentally corrected the syntax errors, it would still be 
*semantically* in error, which you had known if you knew the first thing 
about these languages: “obj” would refer to a *Function* instance that, when 
called in non-strict mode, returned “undefined”; a function that, when 
called in strict mode, would throw a ReferenceError exception because “this” 
would be “undefined”.

The correct code – also called the Module Pattern – is

  var obj = (function () {
    /* The underscore for privates is a matter of preference only */
    var _private;
   
    return {
      setPrivate: function (val) {
        _private = val;
      },
   
      getPrivate: function () {
        return _private;
      }
    };
  }());

You should not consider applying for another job of this kind before you 
have understood and can explain in correct terminology why this is the 
correct code.  This is _not_ “JavaScript 101”.  Do your own homework.

<http://PointedEars.de/faq#posting>

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PointedEars

Twitter: @PointedEars2
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