Re: puzzled by example code using the logical OR

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From	Joao Rodrigues <groups_jr-1@yahoo.com.br>
Newsgroups	comp.lang.javascript
Subject	Re: puzzled by example code using the logical OR
Date	Mon, 23 Feb 2015 23:09:37 -0300
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On 02/23/2015 04:20 PM, JeffG wrote:
> I've been looking at a discussion of creating objects that are containers of all related functions and vars. An example first step is as follows:
> ar AppSpace = AppSpace || {};
> I don't see the purpose of "||". I would appreciate an explanation since I cannot get a response from the author.
> I thought the logical OR only returns true or false based on comparing two values or expressions.
>

According to the ES 5.1, §11.11 (Binary Logical Operators), "The value 
produced by a && or || operator is not necessarily of type Boolean. The 
value produced will always be the value of one of the two operand 
expressions".
<http://ecma-international.org/ecma-262/5.1/#sec-11.11>

Also, as described in ES 5.1, §9.2 (ToBoolean), there are seven "falsy" 
values: false, +0, -0, "", NaN, null, and undefined. All other values 
are "truthy".
<http://ecma-international.org/ecma-262/5.1/#sec-9.2>

So, AppSpace || {} is evaluated as follows:

If ToBoolean(AppSpace) is true, return AppSpace; otherwise, return {} 
(an empty object).

But it is a tad efficient to use:

var AppSpace;
if (!AppSpace) {
   AppSpace = {};
}

Or simply:

var AppSpace;
if (!AppSpace) AppSpace = {};

The logical operators may be described in the following table:
<https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Logical_Operators>

-- 
Joao Rodrigues

Thread

puzzled by example code using the logical OR JeffG <jeffgutsell@fuse.net> - 2015-02-23 11:20 -0800
  Re: puzzled by example code using the logical OR "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2015-02-23 21:57 +0100
    Re: puzzled by example code using the logical OR Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-02-23 21:57 +0000
      Re: puzzled by example code using the logical OR Denis McMahon <denismfmcmahon@gmail.com> - 2015-02-23 22:10 +0000
        Re: puzzled by example code using the logical OR Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-02-23 23:39 +0100
      Re: puzzled by example code using the logical OR Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-02-23 23:12 +0100
  Re: puzzled by example code using the logical OR Joao Rodrigues <groups_jr-1@yahoo.com.br> - 2015-02-23 23:09 -0300
    Re: puzzled by example code using the logical OR Joao Rodrigues <groups_jr-1@yahoo.com.br> - 2015-02-23 23:26 -0300

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