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NOT (!) - JavaScript | MDN
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NOT (!)

Baseline Widely available

This feature is well established and works across many devices and browser versions. Its been available across browsers since 2015 7.

NOT (!) ( , ) , . () . , true false , true .

In this article

const a = 3;
const b = -2;

console.log(!(a > 0 || b > 0));
// Expected output: false

js
!x

true false . , true .

true , . false , .

.

  • null;
  • NaN;
  • 0;
  • ("" or '' or ``);
  • undefined.

! , . ( ) NOT (!!) Boolean .

NOT

!( NOT) .

js
!true; // !t  false 
!false; // !f  true 
!""; // !f  true 
!"Cat"; // !t  false

NOT (!!)

NOT 2 . " " " " ( ).

Boolean .

js
!!true; // !!truthy true .
!!{}; // !!truthy true .  object   .
!!new Boolean(false); // .valueOf() false   !
!!false; // !!falsy false .
!!""; // !!falsy false .
!!Boolean(false); // !!falsy false .

NOT

js
!!bCondition

.

js
bCondition

Specification
ECMAScript 2027 LanguageSpecification
# sec-logical-not-operator

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