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0017. off follows the underlying emitter: Node on the server, component-emitter on the client

Status: Accepted · 2026-08-04 · #103 Governed by: 0000

TL;DR socket.io's server socket is Node's EventEmitter and its client is component-emitter, so their off differs. smocket reproduces both: the server requires a listener and off(event) throws, while the client's no-listener forms clear.

Decision​

Measured against real socket.io 4.8.3, off splits by side because the two sockets are built on different emitters.

On the server socket (Node's EventEmitter, whose off is removeListener) a listener is required: off(event) with none throws a TypeError, so bulk removal is removeAllListeners. On the client socket (component-emitter) the no-listener forms do not throw: off() clears every listener, off(event) clears that event, and off(event, listener) removes one. smocket exposes each side's shape, and the client contract widens off to match rather than forcing the server's stricter signature on it.

Two behaviours are shared and were also measured. off(listener) removes a registration made through once, because the wrapper carries the original listener and both sides compare against it; smocket does the same and removes the first match only. A catch-all (onAny) survives removeAllListeners(), because it is kept in a separate store, on the real side and here.

Because this reproduces the measured real behaviour of both emitters rather than inventing one, it is conformance, not a divergence, so it is not an entry in differences.md. It is recorded here because it reverses the off(event) bulk form the issue proposed, and because the server/client split is not obvious from the API. Emitter mutations return their receiver and therefore remain fluent. Decision 0035 records the wider inherited surface and the Server declaration and runtime return conflict.

Alternatives rejected​

  • One uniform off on both sides. Whichever emitter it copied, it would diverge from the other real socket, so a test could not compare one behaviour across the two sides.
  • off(event) as a bulk remove on the server too, as the issue first proposed. A real server socket throws there rather than clearing, so reproducing a bulk remove would invent a behaviour the server does not have.