true && 1
> 1
true && !!1
> true

Welcome to Javascript

It's not that surprising since (!1) is 'boolean'

It looks perfectly sane to me. 1 is loosely equal to true. Thus, !1 evaluates to false. !!1 then evaluates to false before negating the expression with the remaining ! to ultimately evaluate to true. Also, logical AND and OR operators loosely evaluates the expressions from left to right which in the first example becomes "true && true"

@wessberg yes, but the thing that made me scratch my head is that true && 1 returns 1 instead of true :/

false && X == false
true && X == X
false || X == X
true || X == true

easy as that.
First and last one work even if X throws an error

Is an expresion, not an statement

Why do you even need to do something like true && 1 in your code :-)

@tomabolt I don't, it's for illustration purpose only