Javascript: Is my variable NaN or is it a Number?

Question

I'm not able to establish if my javascript variable is a number or not.

Here's what I have:

alert('variable startDateB: ' + startDateB);

Results:

variable startDateB: NaN

In the very next line I have:

alert('typeof startDateB: '  + typeof(startDateB));

Results:

typeof startDateB: number

My end goal is to compare this date with other dates, but I don't know whether a conversion is necessary since I appear to be getting mixed information about the variable's data type.

Any help is greatly appreciated!

Thanks!

The special value `NaN` **is** a number. – Pointy Feb 05 '18 at 13:50 — Pointy, Feb 05 '18 at 13:50
`console.log(typeof NaN)` – epascarello Feb 05 '18 at 13:52 — epascarello, Feb 05 '18 at 13:52

score 3 · Accepted Answer · answered Feb 05 '18 at 13:53

By definition, NaN is the return value from operations which have an undefined numerical result.

Aside from being part of the global object, it is also part of the Number object: Number.NaN.

This is why you are seeing the behavior you describe. NaN is part of the Number object.

It is still a numeric data type, but it is undefined as a real number.

Javascript: Is my variable NaN or is it a Number?

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