This garbage demo uses a morphing library (Datastar which may switch to using morplex in future) to morph in around 12k divs per frame on any change by any user.

The event listener part is easy use a top level event handler and bubble up events.

The network part is also easy brotli compression over an SSE stream. Even though this demo returns around 180kb per frame uncompressed, a single check between frames will compress to 13bytes on the wire.

https://checkboxes.andersmurphy.com/