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Re: what does var adc = adc || {}; mean?

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From Gregor Kofler <usenet@gregorkofler.com>
Newsgroups comp.lang.javascript
Subject Re: what does var adc = adc || {}; mean?
Date Thu, 28 Jun 2012 00:32:11 +0200
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Am 2012-06-27 23:17, Gene Wirchenko meinte:
> On Wed, 27 Jun 2012 19:28:46 +0200, Gregor Kofler
> <usenet@gregorkofler.com> wrote:
>
>> Am 2012-06-27 16:59, von kristoff meinte:
>>> var adc = adc || {};
>>>
>>> im building an object .. but why is the logical or there? any insite?!
>>>
>>> is it 'create adc' but if adc exists - then use adc .. ?
>>
>> Sort of. If adc evaluates to false (boolean false, undefined, 0, ...)
>> adc is initialized as empty object, otherwise adc keeps its value or
>> reference.
>
>       Because adc is being declared in that very statement, how could
> it have a value other than undefined in the assignment expression?

(Re-)declaring a variable within a certain scope doesn't change or reset 
it's value.

var foo = 10;

...

var foo = foo || 20;

console.log(foo); // 10


I suppose situations without the var are more frequent:

function foo(bar) {
   bar = bar || 42;
   ...
}

though a

function foo(bar) {
   var bar = bar || 42;
   ...
}

wouldn't do any harm.

Gregor

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Thread

what does var adc = adc || {}; mean? von kristoff <mrjcnicolas@gmail.com> - 2012-06-27 07:59 -0700
  Re: what does var adc = adc || {}; mean? Mike Winter <usenet@michael-winter.me.invalid> - 2012-06-27 18:04 +0100
  Re: what does var adc = adc || {}; mean? Gregor Kofler <usenet@gregorkofler.com> - 2012-06-27 19:28 +0200
    Re: what does var adc = adc || {}; mean? Gene Wirchenko <genew@ocis.net> - 2012-06-27 14:17 -0700
      Re: what does var adc = adc || {}; mean? Gregor Kofler <usenet@gregorkofler.com> - 2012-06-28 00:32 +0200
        Re: what does var adc = adc || {}; mean? Gene Wirchenko <genew@ocis.net> - 2012-06-27 19:22 -0700
        Re: what does var adc = adc || {}; mean? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-06-30 10:54 +0200
  Re: what does var adc = adc || {}; mean? von kristoff <mrjcnicolas@gmail.com> - 2012-06-27 11:46 -0700
  Re: what does var adc = adc || {}; mean? Scott Sauyet <scott.sauyet@gmail.com> - 2012-06-28 06:53 -0700

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