JavaScript: How to circumvent the typeof NaN issue?

Question

console.log(typeof NaN)

The above returns 'number'.

Q1. How do I find a way around this?

Q2. What is a better way to find the type of a variable? (instead of typeof)

Thanks!

Update: Thank you for all your comments. But the first answerer understood my question. I was concerned about assessing the type of a return statement of 'NaN' to not show up as a 'Number'.

I was using typeof() in an if statement to act when if(typeof(x) == "number") { do this.. }

But the condition passed even though x was NaN. I wanted to resolve this.

I did not know 'NaN' was of type 'Number' cause NaN means 'Not a Number'. That led to confusion.

I apologize for not being clear on what I wanted to ask. But my issue is solved.

Thanks everyone!

Q1. way around what? typeof returning what the spec says it will? 2. what's wrong with using typeof? — djechlin, Apr 08 '16 at 22:40
Related: [Why does typeof NaN return 'number'?](http://stackoverflow.com/questions/2801601/why-does-typeof-nan-return-number) — Jonathan Lonowski, Apr 08 '16 at 22:44
@Sunny - According to the spec. NaN is of type Number. But the method above will fail for both null and arrays. See my answer below. — arc.slate .0, Apr 08 '16 at 22:48
@MarkReed to be fair it does stand for "Not a number," which would seem to preclude it being a number. — djechlin, Apr 08 '16 at 22:50
Point. Its not-a-number-ness applies to its value rather than its type, but I can understand the confusion. — Mark Reed, Apr 08 '16 at 22:55

Mehdi · Answer 1 · 2016-04-08T22:57:15.710

0

If you want to check whether a number is not NaN, you may want to use isNaN function:

var val = 4

console.log(isNaN(val)) // false

var val2 = NaN

console.log(isNaN(val2)) // true

To check whether a variable contains a number and is not NaN You may then use the following:

typeof val === 'number' && !isNAN(val)

edited Apr 08 '16 at 22:57

answered Apr 08 '16 at 22:55

Mehdi

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But be advised that `isNaN(undefined)` is `true`. – Mark Reed Apr 08 '16 at 22:56
This helps too. Thank you! – Sunny Bharadwaj Apr 08 '16 at 23:56

arc.slate .0 · Accepted Answer · 2016-04-08T22:47:21.157

-2

Don't use typeof unless speed is a need it fails for both arrays and null. However according to the spec NaN is in fact of type Number.

Use

var getType = function (obj) {
    return Object.prototype.toString.call(obj).slice(8, -1);
};

edited Apr 08 '16 at 22:47

answered Apr 08 '16 at 22:41

arc.slate .0

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Reference error: Pub is not defined. – djechlin Apr 08 '16 at 22:43
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And also: what? Seems to return typeof only with the first letter capitalized. Including Nan --> "Number" which seems to be the OP's complaint. And it internally calls typeof I'm pretty sure. This isn't "better" in any way. – djechlin Apr 08 '16 at 22:45
This is from a library. I've edited it for you to use stand alone. – arc.slate .0 Apr 08 '16 at 22:45
Thank you for understanding my issue. This solves it! Thank you! – Sunny Bharadwaj Apr 08 '16 at 22:56

JavaScript: How to circumvent the typeof NaN issue?

2 Answers2