Boolean

The boolean type has only two values: true and false. They are often used in conditions and logical operations.

let isLogged = true;
let isReady = false;

Booleans result from comparisons:

console.log(5 > 3); // true
console.log(5 === 3); // false

They can also be created with the Boolean function or double NOT (!!):

console.log(Boolean(0)); // false
console.log(Boolean("hello")); // true
console.log(!!"hello"); // true

Falsy values (evaluate to false): false, 0, ” (empty string), null, undefined, NaN. Everything else is truthy.