NaN% is the percentage equivalent of the fraction sitemap.xml/undefined. This result comes from the fact that dividing by an undefined value does not produce a real number, so the percentage is not a number.
When you see “NaN%” it simply means the calculation cannot be expressed as a standard numeric percentage. It’s a placeholder that tells you the operation didn’t return a valid result.
In practice, you’ll want to check the inputs and make sure both the numerator and denominator are defined before trying to turn a fraction into a percentage. This avoids getting a “NaN%” answer.
