I was looking for a NodeJS Activity Pub library, and the only promising one I found looks to be only partially complete. That said, I think most Fediverse platforms use implementations in other languages: Rust (Lemmy) , PHP (Kbin), Ruby (Mastadon), etc).
Several frontends use NodeJS, though. Perhaps you can contribute there or even contribute to Actvitypub-Express to bring that to feature completion?