Posted almost 8 years ago. Visible to the public.

JavaScript: How to check if an object is NaN

JavaScript's NaN ("Not a Number") is hard to compare against. It never equals anything, not even itself:

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NaN === NaN; // false Number.NaN === NaN; // false

There is the isNaN method, but it is not really what you are looking for:

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isNaN(NaN) // true isNaN('hello') // true

Option 1: ES6

The Object.is() method determines whether two values are the same value. It even works for NaN:

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Object.is(NaN, NaN) // true

Option 2: ES5

The example above shows that simply using isNaN would match other objects, too. However, look at the weird type of "Not a Number":

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typeof NaN // "number"

Hence we can actually check against NaN like this:

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var something = NaN; typeof something === 'number' && isNaN(something) // true

Wow.

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Arne Hartherz
Last edit:
almost 3 years ago
by Johanna Schalk
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Posted by Arne Hartherz to makandra dev
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