null
The null value represents the intentional absence of any object value. It
is one of JavaScript's primitive values and
is treated as falsy for boolean operations.
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Syntax
js
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.
js
// foo does not exist. It is not defined and has never been initialized:
foo; //ReferenceError: foo is not defined
js
// foo is known to exist now but it has no type or value:
const 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.
js
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
Number.isNaN(1 + null); // false
Number.isNaN(1 + undefined); // true
Specifications
| Specification |
|---|
| ECMAScript Language Specification # sec-null-value |
Browser compatibility
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