Description In JavaScript NaN is short for "Not-a-Number". The isNaN() method returns true if a value is NaN. The isNaN() method converts the value to a number before testing it.

Jul 8, 2025 · The isNaN() function answers the question "is the input functionally equivalent to NaN when used in a number context". If isNaN(x) returns false, you can use x in an arithmetic expression …

Jul 23, 2025 · The JavaScript isNaN () Function is used to check whether a given value is an illegal number or not. It returns true if the value is a NaN else returns false. It is different from the …

Apr 16, 2010 · 182 I just came across this technique in the book Effective JavaScript that is pretty simple: Since NaN is the only JavaScript value that is treated as unequal to itself, you can always …

Nov 2, 2025 · In this blog, we’ll demystify `NaN`, explore why checking for it is non-trivial, and dive deep into the differences between `isNaN ()` and `Number.isNaN ()`. By the end, you’ll understand when …

Feb 5, 2025 · A comprehensive guide to the JavaScript isNaN () function, explaining how it checks if a value is NaN (Not-a-Number), its quirks, and how to use it effectively.

Understand how JavaScript isNaN works, its quirks with type coercion, and when to use Number.isNaN instead. Includes real examples and best practices.

In this comprehensive guide, I‘m going to walk you through everything you need to know about the isNaN() function in JavaScript. We‘ll explore its inner workings, quirks, practical applications, and …

Jul 10, 2025 · The Number.isNaN() static method determines whether the passed value is the number value NaN, and returns false if the input is not of the Number type. It is a more robust version of the …

isNaN() is a top-level function and is not associated with any object. If the argument is not of type Number, the value is first coerced to NaN and then checked.