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

See also

• undefined
• NaN