W3cubDocs

/JavaScript

null

The value null represents the intentional absence of any object value. It is one of JavaScript's primitive values.

Syntax

null

Description

The value null is written with a literal: null. null is not an identifier for a property of the global object, like undefined can be. Instead, null expresses a lack of identification, indicating that a variable points to no object. In APIs, null is often retrieved in a place where an object can 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:
var foo = null; foo;
"null"

Difference between null and undefined

When checking for null or undefined, beware of the differences between equality (==) and identity (===) operators, as the former performs type-conversion.

typeof null        // "object" (not "null" for legacy reasons)
typeof undefined   // "undefined"
null === undefined // false
null  == undefined // true
null === null //true
null == null //true
!null // true
isNaN(1 + null) //false
isNaN(1 + undefined) //true

Specifications

Browser compatibility

Feature Chrome Edge Firefox (Gecko) Internet Explorer Opera Safari
Basic support (Yes) (Yes) (Yes) (Yes) (Yes) (Yes)
Feature Android Chrome for Android Edge Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support (Yes) (Yes) (Yes) (Yes) (Yes) (Yes) (Yes)

See also

© 2005–2017 Mozilla Developer Network and individual contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/null