You can't have circular dependencies in ES6 modules (although it's probably good to avoid them regardless) so unfortunately I did have to make some pretty drastic changes to the project. I haven't tried to make it pretty at this point, as I just wanted this done for my own purposes. However, if you're interested I'll submit pull requests and clean-up accordingly.
I don't know if this is something you're interested in, so I figured I'd open an issue before submitting any pull requests.
Basically I've forked this repo and its dependencies and made them all into ES6 modules that build with rollup:
https://github.com/Benjamin-Dobell/msgpack-lite https://github.com/Benjamin-Dobell/event-lite https://github.com/Benjamin-Dobell/int64-buffer
You can't have circular dependencies in ES6 modules (although it's probably good to avoid them regardless) so unfortunately I did have to make some pretty drastic changes to the project. I haven't tried to make it pretty at this point, as I just wanted this done for my own purposes. However, if you're interested I'll submit pull requests and clean-up accordingly.