JavaScript .isNaN()

The Number.isNaN() method is part of the Number class in JavaScript.

It accepts a single argument, value, and returns true if the passed argument is NaN (“Not a Number”), and returns false, otherwise.

Syntax

Number.isNaN(value);

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• value (required): The value to check.

Example 1

To verify if 0 / 0 is NaN:

const x = 0 / 0;

console.log(Number.isNaN(x));
// Output: true

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The square root of a negative number would return NaN, so it would return true.

Example 2

To verify if 5 is NaN:

const y = 5;

console.log(Number.isNaN(y));
// Output: false

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It would return false because 5 is a number.

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