What is the Not Not Operator in JavaScript

In this article, we will learn about the !! (not not) operator in JavaScript.This double negation forces a value to be evaluated as either true or false.

What is the !! Operator?

The double negation(!! ) operator is the! Operator twice and calculates the truth value of a value. It returns a Boolean value, which depends on the truthiness of the expression. 

How It Works:

• The first ! negates the value, converting it to true or false.
  
• The second ! negates it again, effectively converting it into a strict boolean (true or false).

Consider (!!p) as !(!p), here's an example ?

If p is a false value, !p is true, and !!p is false.
If p is a true value, !p is false, and !!p is true.

Truthy and Falsy Values

In JavaScript values are inherently truthy or falsy when evaluated in a boolean context. The !! operator uses this behavior to convert any value to true or false.

Falsy Values ?

false
0
"" (empty string)
null
undefined
NaN

All other values are considered truthy.

Example

Below is an example for the !! (not not) operator in JavaScript ?

console.log(!!"Hello");  
console.log(!!0);        
console.log(!!null);     
console.log(!![]);       
console.log(!!{});    

Output

true
false
false
true
true

Example

conditional statements or when passing a value to a function that expects a boolean ?

let input = "";

if (!!input) {
    console.log("Input has a value.");
} else {
    console.log("Input is empty."); // This will execute
}

Output

Input is empty.

Conclusion

The !! operator is a simple yet powerful way to convert any value to a boolean in JavaScript. It is especially useful when working with conditional logic checking variable existence, and ensuring valid data.