Ask HN: Is it feasible to have just a REST API as a back end for web app?

Read about this approach at a few places: Have only a REST API as a backend and do everything else in the frontend JS framework.

I don't know enough about web architectures to evaluate this approach. Is it possible to develop a site/app with this approach regardless of complexity of the app, or is this only suitable for certain scenarios?

Any help would be greatly appreciated.