Groups > comp.lang.javascript > #20121

Re: No existing object

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Message-ID	<2326659.jpX2h7uNEo@PointedEars.de> (permalink)
From	Thomas 'PointedEars' Lahn <PointedEars@web.de>
Reply-To	Thomas 'PointedEars' Lahn <usenet@PointedEars.de>
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Subject	Re: No existing object
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Andrew Poulos wrote:

> If I have a constructor:
> 
> var Foo = function(el) {
>    this.elem =...
> };
> Foo.prototype.reset = function() {
>     ...
> };
> 
> and then its used like this
> 
> var a = new Foo("elem1");
> var b = new Foo("elem2");
> var c = new Foo("elem3");
> 
> ...
> a.reset();
> a = null;
> 
> How can I know if there are no objects constructed from Foo still
> existing?

You cannot.

> Should I just put a counter into the constructor and then decrement it
> when reset is called?

Depending on what this is for, putting a prototype-local counter (to 
restrict access), increasing it with each constructor call and decreasing it 
with each call of reset() might be a good idea.  I suggest naming “reset” 
“destroy” then, instead.

  function Foo ()
  {
    this.inc();
  }

  Foo.prototype = (function () {
    var counter = 0;
    
    var _Foo_prototype = {
      constructor: Foo,

      inc: function () {
        ++counter;
      },

      destroy: function () {
        --counter;

        if (counter <= 0)
        {
          /* all done */
        }
      }
    };

    if (Object.defineProperty == "function")
    {
      try
      {
        Object.defineProperty(_Foo_prototype, "constructor", {
          value: Foo
        });
      }
      catch (e)
      {
        /* borken implementation, like JScript 9.0 */
      }
    }

    return _Foo_prototype;
  }());

or with JSX:

  var Foo = (function () {
    this.inc();
  }).extend(null, (function () {
    var counter = 0;

    return {
      inc: function () {
        ++counter;
      },

      destroy: function () {
        --counter;

        if (counter <= 0)
        {
          /* all done */
        }
      }
    };
  }()));

Untested.

-- 
PointedEars

Twitter: @PointedEars2
Please do not Cc: me. / Bitte keine Kopien per E-Mail.

Thread

No existing object Andrew Poulos <ap_prog@hotmail.com> - 2013-06-03 08:26 +1000
  Re: No existing object Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2013-06-03 01:24 +0200
    Re: No existing object Scott Sauyet <scott.sauyet@gmail.com> - 2013-06-03 05:45 -0700
      Re: No existing object Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2013-06-03 15:04 +0200
        Re: No existing object Scott Sauyet <scott.sauyet@gmail.com> - 2013-06-03 10:04 -0700
  Re: No existing object John Harris <niam@jghnorth.org.uk.invalid> - 2013-06-03 14:30 +0100
    Re: No existing object Andrew Poulos <ap_prog@hotmail.com> - 2013-06-04 08:05 +1000
      Re: No existing object John Harris <niam@jghnorth.org.uk.invalid> - 2013-06-04 10:57 +0100

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