how can i get the full name of the country from the customer’s addresbook? while looping through the addressbook and using this code, i only got the abbreviated country code

var country = customer.getSublistText('addressbook', 'country_initialvalue', i);

You probably want to get the subrecord

if i get the subrecord, can i extract different parts of the address from the subrecord?

yup

i’m trying to get the full country name of the default billing address, but subrecord gives me a completely different address from the sublist

the countries list is slow changing. You could use a static lookup like this https://github.com/ExploreConsulting/netsuite-fasttrack-toolkit-ss2/blob/master/geography.ts