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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

Specification Status Comment
ECMAScript 1st Edition (ECMA-262) Standard Initial definition.
ECMAScript 5.1 (ECMA-262)
The definition of 'null value' in that specification.
Standard  
ECMAScript 2015 (6th Edition, ECMA-262)
The definition of 'null value' in that specification.
Standard  
ECMAScript Latest Draft (ECMA-262)
The definition of 'null value' in that specification.
Living Standard  

Browser compatibility

FeatureChromeEdgeFirefoxInternet ExplorerOperaSafari
Basic support Yes Yes Yes Yes Yes Yes
FeatureAndroid webviewChrome for AndroidEdge mobileFirefox for AndroidIE mobileOpera AndroidiOS Safari
Basic support Yes Yes Yes Yes Yes Yes Yes

See also

Štítky a přispěvatelé do dokumentace

 Poslední aktualizace od: fscholz,