what does " !! "mean in this code ? and what does the first if statement mean?

Question

var num = 20;
if ( !! num || ! num && num - num){
console.log("A");
} else if (num == 20) {
console.log("C")
} else {
console.log("B");
}

Answer 1

! = NOT
! true = false
! false = true

!! = NOT NOT
!! true = true
!! false = false

!!! true = false
!!! false = true

https://medium.com/@edplatomail/js-double-bang-or-the-not-operator-part-40e55d089bf0

!! num returns true.
! num returns false
|| OR (true || true = true, false || true = true, true || false = true)
&& AND (only true for true && true)

if(true OR false && 0)

false AND 0 returns false
true || false returns true

-> the whole condition in if statement is true

output: A

But don't ask me about the sense of such a condition ;)

Edit: Maybe it is just an exercise about boolean

Answer 2

!!X === !(!X) === Boolean(X)
!X === !(Boolean(X))
For me the first if statement has not meaning.

Answer 3

A trick to convert a number to its boolean form.