that's for "True" conditions.
No, it's for any value. !! will convert any value in it's equivalent Boolean value.
Why? Because the not operator simply returns the opposite Boolean value. So
0 // is falsy
!0 // -> true
!!0 // -> false
'foo' // is truthy
!'foo' // -> false
!!'foo' // -> true
Any additional application will just toggle the value again. Thus !!! is equivalent to ! and !!!! is equivalent to !! and so on.
