NaN
The global NaN
property is a value representing Not-A-Number.
Property attributes of NaN |
|
---|---|
Writable | no |
Enumerable | no |
Configurable | no |
Syntax
NaN
Description
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
NaN
compares unequal (via ==
, !=
, ===
, and !==
) to any other value -- including to another NaN value. Use Number.isNaN()
or isNaN()
to most clearly determine whether a value is NaN. Or perform a self-comparison: NaN, and only NaN, will compare unequal to itself.
NaN === NaN; // false Number.NaN === NaN; // false isNaN(NaN); // true isNaN(Number.NaN); // true function valueIsNaN(v) { return v !== v; } valueIsNaN(1); // false valueIsNaN(NaN); // true valueIsNaN(Number.NaN); // true
Specifications
Specification | Status | Comment |
---|---|---|
ECMAScript 1st Edition (ECMA-262) | Standard | Initial definition. Implemented in JavaScript 1.3 |
ECMAScript 5.1 (ECMA-262) The definition of 'NaN' in that specification. |
Standard | |
ECMAScript 2015 (6th Edition, ECMA-262) The definition of 'NaN' in that specification. |
Standard | |
ECMAScript 2017 Draft (ECMA-262) The definition of 'NaN' in that specification. |
Draft |
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
License
© 2016 Mozilla Contributors
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-us/docs/web/javascript/reference/global_objects/nan