JavaScript: variable = variable || variable

Question

I have absolutely no idea how this is called which is the reason why my searches failed miserably.

What does this code mean

var a = b || c;

I believe it's something like a will equal which ever is defined but.. I just have to be sure what it exactly does before I use it.

It is a boolean OR operation, a way you could search for it is "javascript double pipe operation", just for future reference :) — Jaime Gómez, Jul 31 '14 at 21:23
Yes, this is one of the things I wanted to find out, asking this question, thank you! — php_nub_qq, Jul 31 '14 at 21:25

score 2 · Accepted Answer · answered Jul 31 '14 at 21:21

2

If b is defined, it will use b, if c is defined and b isn't, it will use c. If you put it in parenthesis () it will return true/false.

answered Jul 31 '14 at 21:21

Blake A. Nichols

what if both are defined, are there docs for this :? – php_nub_qq Jul 31 '14 at 21:22
In this context it makes sense to define "defined" more precisely. – Felix Kling Jul 31 '14 at 21:23
@php_nub_qq: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Logical_Operators#Logical_OR_(.7C.7C) – Felix Kling Jul 31 '14 at 21:23
1

if both are defined it will use b. It stops evaluating as soon as its gets a valid (not null/false/undefined/0/empty string). – Blake A. Nichols Jul 31 '14 at 21:23
@BlakeA.Nichols but if I need to set a default value of `false` how would that work – php_nub_qq Jul 31 '14 at 21:27
1

var a = b || c || false; – Blake A. Nichols Jul 31 '14 at 21:29
*"If you put it in parenthesis () it will return true/false."* What? – Felix Kling Aug 01 '14 at 00:20

1 Answers1