By a quick glance, yes, this is what I want: a channel to communicate between processes via a piece of shared memory, protected by a pair of futexes.
In JS ecosystem, buffers that allow data loss is more common (aka ring buffers), but ringbuf.js [1] is the only complete implementation to my knowledge. In my use case on I/O between WASM modules where data must be transferred as-is, the process must block on buffer overrun/underrun in a synchronous manner. Therefore a circular buffer is required. I could not find such a niche library written in JS, so I decided to bite the bullet and reinvent the wheel [2].