null
The value null
represents the intentional absence of any object value. It
is one of JavaScript's primitive values and
is treated as falsy for boolean operations.
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
Examples
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 |
---|
ECMAScript Language Specification # sec-null-value |
Browser compatibility
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