JavaScript: what is NaN, Object or primitive?

Question

what is NaN, Object or primitive?

NaN - Not a Number

NaN is like NULL. you can refer this [SO Post][1] [1]: http://stackoverflow.com/questions/559792/what-is-the-reserved-keyword-for-nan-in-javascript — avani gadhai, May 08 '12 at 12:28
@rsplak: `NaN` is also a property of the global object, both have the value `NaN`. — Andy E, May 08 '12 at 12:30
Have a look at the specification [here](http://es5.github.com/#x8.5) and [here](http://es5.github.com/#x15.1.1.1) for more information about `NaN`. — Felix Kling, May 08 '12 at 12:42
@avanigadhai Not exactly. `null` is actually a type, with only one value: `null`. — kapa, May 08 '12 at 13:33

Dagg Nabbit · Answer 1 · 2012-05-08T12:48:38.253

15

It's a primitive. You can check in a number of ways:

typeof NaN gives "number," not "object."
Add a property, it disappears. NaN.foo = "hi"; console.log(NaN.foo) // undefined
NaN instanceof Number gives false (but we know it's a number, so it must be a primitive).

It wouldn't really make sense for NaN to be an object, because expressions like 0 / 0 need to result in NaN, and math operations always result in primitives. Having NaN as an object would also mean it could not act as a falsey value, which it does in some cases.

edited May 08 '12 at 12:48

answered May 08 '12 at 12:32

Dagg Nabbit

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note that NaN !== NaN gives true. – A. Kürşat UZUN Oct 14 '21 at 07:46

score 9 · Accepted Answer · answered May 08 '12 at 12:23

9

NaN is a primitive Number value. Just like 1, 2, etc.

answered May 08 '12 at 12:23

kapa

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score 2 · Answer 3 · edited May 08 '12 at 13:19

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")).

Reference

Vaibhav Chobisa · Answer 4 · 2023-05-02T08:12:02.677

0

Would like to add some observations about NaN that intrigued me:

typeof(NaN) returns 'number', but isNaN(NaN) returns true

Funny.

Also,

isNaN(10) and isNaN('10') both return false
isNaN('') returns false, but isNaN('any alphabetical string') returns true
isNaN(true) and isNaN(false) return false. So boolean values are also considered as a number by isNaN function.

edited May 02 '23 at 08:12

answered May 02 '23 at 07:41

Vaibhav Chobisa

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JavaScript: what is NaN, Object or primitive?

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