How to work Javascript API Atlassian Bitbucket?

I am successfully using AP.require ('url' ..),url: api.bitbucket.org/2.0/,

but I don’t understand how to work with these javacript api bitbucket modules and how they interact with bitbucket.For example:https://docs.atlassian.com/bitbucket-server/docs/5.6.2/reference/javascript/bitbucket_util_navbuilder.html

Where to get 'bitbucket / util / navbuilder' and what is it for?