javascript if else shorthand and strings

Question

var x = 'x' 
x-'m'||console.log('True 1') 
// logs True, should be false

var x = '2' 
x-2||console.log('True 2') 
// logs True

var x = '3' 
x-2||console.log('True 3') 
// logs False

Why does this if else shorthand always return true when using a string? How can it be fixed?

I learnt this from here

`NaN` is falsy. it logs only the first with `NaN` and the second with zero. — Nina Scholz, May 07 '20 at 13:51
I think by "logs false" he means "doesn't go in the console.log". — Aioros, May 07 '20 at 13:53
How are you reading the expression `x-'m'||console.log('True 1') ` : `x-( 'm'||console.log('True 1') )` - so "should not log anything because `'m'` is truthy" or `( x-'m' ) ||console.log('True 1')` - "should not log anything because `x-'m'` is truthy"? — VLAZ, May 07 '20 at 14:05

score 0 · Accepted Answer · answered May 07 '20 at 13:57

If the expression before the || returns a falsy expression, then the console.log() is executed. This happens for the first expression 'x' - 'm' which produces NaN (which is falsy):

console.log('x' - 'm')

and for the second expression '2' - 2 which returns 0 (which is falsy):

console.log('2' - 2)

Your console.log() does not get executed for the third expression '3' - 2 because that returns 1 (which is truthy):

console.log('3' - 2)

javascript if else shorthand and strings

1 Answers1