var packbuilder = new NodeGit.Packbuilder();
results in -> [Error: A new GitPackbuilder cannot be instantiated.]

From the docs http://www.nodegit.org/api/#Packbuilder , it seems that Packbuilder only has Instance methods to use Packbuilder, and no Class methods to create an instance of it. I'm also not able to create a "new" instance of Packbuilder from Js, and can't find a reference on other objects to an existing instance.