isNaN function in nodejs

Question

why is isNaN function in nodejs returning false in the following cases?

isNaN(''),isNaN('\n'),isNaN('\t')

this is very weird.

does somebody have any ideas as I thought isNaN stood for is Not a Number.

can someone please clarify

Thanks in advance!

Answer 1

Because you are not passing it a number, it will convert it to number. All of those convert to 0 which is 0 and not NaN

Number('')
0
Number('\n')
0
Number('\t')
0
isNaN(0)
false

Note that NaN does not stand for "not a JavaScript Number". In fact it's completely separate from JavaScript and exists in all languages that support IEEE-754 floats.

If you want to check if something is a javascript number, the check is

if (typeof value === "number") {

}

Answer 2

NaN is a very specific thing: it is a floating point value which has the appropriate NaN flags set, per the IEEE754 spec (Wikipedia article).

If you want to check whether a string has a numeric value in it, you can do parseFloat(str) (MDN on parseFloat). If that fails to find any valid numeric content, or finds invalid characters before finding numbers, it will return a NaN value.

So try doing isNaN(parseFloat(str)) - it gives me true for all three examples posted.

Answer 3

isNan() is designed to help detect things that are 'mathematically undefined' - e.g. 0/0 -

node
> isNaN(0/0)
true
> isNaN(1/0)
false
> isNaN(Math.sqrt(-1))
true
> isNaN(Math.log(-1))
true

The other advice you got here in this question on how to detect numbers is solid.