Rebuy.Js is the front end library that loads in to Shopify stores and powers the Rebuy experience.
For Rebuy widgets, Rebuy looks for divs with attribute of data-rebuy-id="XXX" and will hydrate those elements with Rebuy merchandising components and merchandising widgets.
Rebuy also includes customer identity tracking and event tracking which leverages Shopify's consent tracking API If a customer has declined consent, Rebuy will track event anonymously .
Rebuy JS is very extensible SDK that allows complex work flows to fit your needs. Rebuy JS contains events and public functions which can be found in the respective section of these doc's.