Lozza runs single-threaded in a Web Worker, yet still responds to stop during a search. This example starts go infinite and sends stop a second later. Lozza replies with bestmove, then answers the uci command that was queued behind stop.
At high depths stop can take a while, as it's only checked between iterative deepening iterations. For an immediate stop use worker.terminate() and create a new worker; the hash is lost and there's a short startup delay.