Check out Google FlatBuffers [1], I haven't used in a while but it had a working JS implementation and better language support for other languages than Cap'n Pr

Check out Google FlatBuffers [1], I haven't used in a while but it had a working JS implementation and better language support for other languages than Cap'n Proto last time I needed something and compared the two. It's just a serialization framework and doesn't bundle RPC/distributed objects like Cap'n Proto - no event loop library or the complexity that comes with this - if you just need a serialization I think it's more approachable. [1] https://github.com/google/flatbuffers https://github.com/google/flatbuffers