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.
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.
function getVowels(str) {
const m = str.match(/[aeiou]/gi);
if (m === null) {
return 0;
}
return m.length;
}
console.log(getVowels("sky"));
/ Expected output: 0
null
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:
const foo = null;
foo; / null
null and undefinedWhen 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
Number.isNaN(1 + null); / false
Number.isNaN(1 + undefined); / true
| Specification |
|---|
| ECMAScript® 2026 Language Specification # sec-null-value |