A value representing Not-A-Number.

Core Global Property
Implemented in JavaScript 1.3
ECMAScript Edition ECMAScript 1st Edition




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 isNaN instead.

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

See also

Document Tags and Contributors

 Last updated by: Maian,