How Can I Reliably Check for NaN in JavaScript?

Validating NaN in JavaScript

Checking if a number is NaN (Not a Number) in JavaScript can be tricky. This is because conventional methods such as comparing a value to NaN or using the Number.NaN constant often yield false results.

Specifically, parseFloat('geoff') == NaN will return false in Firefox's JavaScript console, even though 'geoff' is not a valid number.

Solution: Using the isNaN() Function

To accurately validate NaN, JavaScript provides the isNaN() function. Here's how you can use it:

isNaN(parseFloat("geoff"))

This will return true, indicating that the parsed value of 'geoff' is NaN.

Note: The isNaN() function can also be used to check for NaN values in non-numeric data types, such as strings.

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