thank you for this addition.
it looks good to me, only thing I personally don't like is the link to the URL being inside the isPostalCode.js

generally speaking: thank you for providing some official reference for the numbers, and I agree that there should be some place, where all of that information is stored/made available, but I'm not sure if isPostalCode.js would be the best place for that - it would get really messy in that file, otherwise, if every language had 1 or maybe even 2 references in there.