How Can I Reliably Verify if a Value is NaN in JavaScript?

Verifying NaN in JavaScript: The Definitive Solution

When validating floating-point values, determining whether a number is Not a Number (NaN) can be crucial. However, attempting to compare a non-numeric value to NaN directly often leads to unexpected results.

The Pitfall

In your attempts to check for NaN using:

parseFloat('geoff') == NaN;
parseFloat('geoff') == Number.NaN;

you may have encountered falsey outcomes. This is because these expressions attempt to coerce the non-numeric 'geoff' into a floating-point value before comparing, which results in a legitimate number (Infinity) instead of NaN.

The Solution: isNaN()

To accurately identify NaN in JavaScript, it is recommended you utilize the built-in isNaN() function. The syntax is as follows:

isNaN(value)

where value is the variable or expression you want to evaluate for NaN.

Using isNaN(), you can effectively check if a value is NaN, as demonstrated by:

isNaN(parseFloat('geoff')) // true

Note: For more comprehensive NaN checks, especially when dealing with non-numerical values, refer to the resources provided in the answer. By leveraging these approaches, you can ensure precise and robust NaN validation in your JavaScript applications.

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