Why isn't NaN finite?

Question

Testing the isFinite function I see that NaN is an infinite number (even if it's not a number :-)).

isFinite(NaN) // returns false

What's the logic behind this? Why isn't NaN finite?

Answer 1

As Dave Newton said, NaN is not a number, and then you have to consider that it isn't finite nor infinite. The same occurs to these:

NaN > 0  // false
NaN < 0  // false

You might want to read these articles:

• https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/NaN
• https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/isFinite

Answer 2

Because it is not a numeric value...and finite/infinite is applicable only to numbers.

Answer 3

The result of any arithmetic operation on NaN is NaN.

The result of any logic operation on NaN is false.

Answer 4

Because an infinite number... is still a number. NaN isn't a number in any possible sense.

It's like an error in Matrix.

Answer 5

Finite means capable of being counted. It has to return true or false for isFinite. I think it makes more sense for NaN to be infinite.