The book is focused on Spring reactive components, so the WebFlux framework. Since Spring is used for the background heavylifting, the reactive part of the book focuses more on the interaction between reactive microservices. The Web interface is mostly based on reactive Thymeleaf views that can interract with reactive microservices, which seemed to support resyncronization.
HTML5 imbedded DB is not really a topic I considered, because of the focus being on Spring. But I will keep it in mind for the next edition. Thank you!