In javascript, 5 || 0 and 0 || 5 returns 5

Question

As the title says everything. 5 || 0 and 0 || 5 returns 5 in JavaScript. Why does this happen and what does two || means in javascript?

Short-circuit Evaluation: http://en.wikipedia.org/wiki/Short-circuit_evaluation — malifa, Feb 27 '14 at 18:18
Why does everyone seem to be discovering how Javascript's logical operators work this week? Seen this question a few times recently. — deceze, Feb 27 '14 at 18:18
Get a good reference and look things up. https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Logical_Operators — epascarello, Feb 27 '14 at 18:20

score 1 · Accepted Answer · answered Feb 27 '14 at 18:17

1

It's a boolean or, and 5 evaluates to truthy. If you want to force your types to boolean you should use the !! (double negation) like so,

!!(5 || 0)

answered Feb 27 '14 at 18:17

Elliott Frisch

score 1 · Answer 2 · answered Feb 27 '14 at 18:18

1

|| is a boolean or.

5 == true
0 == false

So, 5 || 0 = 5

answered Feb 27 '14 at 18:18

Zero Fiber

score 0 · Answer 3 · answered Feb 27 '14 at 18:19

0

The || is a synonym for the logical OR

So the statement ANY_VALUE || ANY_OTHER_VALUE means that if the first value is truthy then return that else return the second value

answered Feb 27 '14 at 18:19

Lucky Soni

3 Answers3