javascript module dependency implementation

JS beginner here, trying to implement JS library/sdk. Have read through the common patterns and planning to use revealing module pattern as of now. For context, lets take an example. We have a library and people can rent books from library. So the library will expose 2 objects to application - library and rented_book. For simplicity, lets say this library does not maintain list of available books but just rented books.

Now I will create a file called library.js and put the complete module for library object in it. And create another module book.js and code for the same in it. Now my doubts are

1. How do I create the relationship between these two objects. When a user wants to rent a book, should I do a new on the book object and create it
2. How do I make sure that the book module is loaded before the library object?

Basically, I am confused on how to create a library in this way. Any links to stuff that explain this will help a lot.