What does an exclamation mark before a variable mean in JavaScript

Question

I\'m trying to learn JavaScript by going through some code in an application and I keep seeing !variable in if conditions. For example:

if (!va         


        

Answer 1

! is a logic reversal operator, if something was true it will change it to false, if something is false, it will change to true.

example, we know that empty string or 0 in boolean is false.

let a = Boolean("")
console.log(a) // shows false, because empty string in boolean is false
console.log(!a) // shows true, because logic is reversed

easier example:

let a = 5
let b = 1
let c = a > b
console.log(c) // shows true, since a,5 is bigger than b,1
console.log(!c) // shows false, since logic is now reversed