Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.javascript > #26914

Re: puzzled by example code using the logical OR

Show all headers | View raw

On Mon, 23 Feb 2015 21:57:55 +0000, Ben Bacarisse wrote:

> "Evertjan." <exxjxw.hannivoort@inter.nl.net> writes:
> 
>> JeffG <jeffgutsell@fuse.net> wrote on 23 feb 2015 in
>> comp.lang.javascript:
>>
>>> 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.
>>
>> Incorrect. That only happens if || compares boolean values.
>>
>> AppSpace = AppSpace || {};
>>
>> AppSpace is set to AppSpace [so effectivly remains so], unless AppSpace
>> returns false or empty or 0 or undefined, then AppSpace is set to {},
>> an empty object.
> 
> It's false, the empty string, 0 (both +0 and -0), NaNs, undefined and
> null that are considered false.  (It's common not to care about -0 and
> NaNs, but null matters a bit more.)

More generally, when comparing multiple (2 or more) values with ||, from 
left to right, the first "not considered false"[1] value is returned, or 
false if all the values being compared are "considered false"[2].

[1] sometimes referred to as truthy
[2] sometimes referred to as falsey

-- 
Denis McMahon, denismfmcmahon@gmail.com

Back to comp.lang.javascript | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

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

csiph-web