What is the !! (not not) Operator in JavaScript?

The !! (double negation) operator is a repetition of the unary logical "not" (!) operator twice. It is used to determine the truthiness of a value and convert it to a boolean (either true or false). Here’s how it works:

• The single ! (logical "not") inverts the truth value of a given expression:
  • !false becomes true, because "false is not true."
  • !true becomes false, because "true is not false."
• The double negation !! reverses this inversion, converting a value to its boolean equivalent:
  • !!true returns true, because "true is not not true."
  • !!false returns false, because "false is not not false."

In essence, !! forces a value into its corresponding boolean form, reflecting its inherent truthiness.

Example 1: This example checks the truthiness of the boolean value true.

// Declare a variable using let
let n1;

/* Checking the truthiness of
   the boolean value true using !! */
n1 = !!true;

// Log the result to the console
console.log(n1);

true

Example 2: This example checks the falsyness of the boolean value false.

// Declare a variable using let
let n1;

// Checking the falsiness of the boolean value false using !!
n1 = !!false;

// Output the result using console.log
console.log(n1);

false

Example3: This example checks the truthyness or falsyness of a given string.

// Write Javascript code here
let n1;
// checking the truthiness of a given string.
n1 = !!"Javascript programming";

// Output the result (which will be true) 
// using console.log
console.log(n1);

true

Example 4: This example checks the truthyness or falsyness of a given object.

// Write Javascript code here
let n1;
// checking the truthiness 
// of a given object.
n1 = !!{
    articles: 70
};

// Output the result (which will be true) using console.log
console.log(n1);

true