null
BaselineWidely available
This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.
Thenull value represents the intentional absence of any object value. Itis one of JavaScript'sprimitive values andis treated asfalsy for boolean operations.
Try it
function getVowels(str) { const m = str.match(/[aeiou]/gi); if (m === null) { return 0; } return m.length;}console.log(getVowels("sky"));// Expected output: 0Syntax
nullDescription
The valuenull is written with a literal:null.null is not an identifier for a property of the global object, likeundefined can be. Instead,null expresses a lack of identification, indicating that a variable pointsto no object. In APIs,null is often retrieved in a place where an objectcan be expected but no object is relevant.
// foo does not exist. It is not defined and has never been initialized:foo; // ReferenceError: foo is not defined// foo is known to exist now but it has no type or value:const foo = null;foo; // nullExamples
Difference betweennull andundefined
When checking fornull orundefined, beware of thedifferences between equality (==) and identity (===) operators, as the former performstype-conversion.
typeof null; // "object" (not "null" for legacy reasons)typeof undefined; // "undefined"null === undefined; // falsenull == undefined; // truenull === null; // truenull == null; // true!null; // trueNumber.isNaN(1 + null); // falseNumber.isNaN(1 + undefined); // trueSpecifications
| Specification |
|---|
| ECMAScript® 2026 Language Specification # sec-null-value |