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.