The global NaN property is a value representing Not-A-Number.

Property attributes of NaN
Writable no
Enumerable no
Configurable no




NaN is a property of the global object.

The initial value of NaN is Not-A-Number — the same as the value of Number.NaN. In modern browsers, NaN is a non-configurable, non-writable property. Even when this is not the case, avoid overriding it.

It is rather rare to use NaN in a program. It is the returned value when Math functions fail (Math.sqrt(-1)) or when a function trying to parse a number fails (parseInt("blabla")).

Testing against NaN

Equality operator (== and ===) cannot be used to test a value against NaN. Use Number.isNaN() or isNaN() instead.

NaN === NaN;        // false
Number.NaN === NaN; // false
isNaN(NaN);         // true
isNaN(Number.NaN);  // true


Specification Status Comment
ECMAScript 1st Edition. Standard Initial definition. Implemented in JavaScript 1.3
ECMAScript 5.1 (ECMA-262)
The definition of 'NaN' in that specification.
ECMAScript 6 (ECMA-262)
The definition of 'NaN' in that specification.

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
Basic support (Yes) (Yes) (Yes) (Yes) (Yes)
Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support (Yes) (Yes) (Yes) (Yes) (Yes) (Yes)

See also

Document Tags and Contributors

 Contributors to this page: Sevenspade
 Last updated by: Sevenspade,