Events

@oh-just-another/events is a tiny, dependency-free typed event emitter (an L0 package — no DOM, React, or Node APIs). It underpins the pub/sub in Editor, History, and Collab, and you can use it standalone for your own typed channels.

Typed emitter

Declare an event map, then createEmitter gives you a fully typed on / emit / off. Payloads are typechecked and listener arguments are inferred.

import { createEmitter, type Emitter } from "@oh-just-another/events";

interface EditorEvents {
  mode: (mode: "select" | "draw") => void;
  change: () => void;
}

const emitter: Emitter<EditorEvents> = createEmitter<EditorEvents>();

const off = emitter.on("mode", (m) => console.log(m)); // m: "select" | "draw"
emitter.emit("mode", "select"); // returns the number of listeners run
off(); // idempotent unsubscribe

Behaviour

• on(event, fn) returns an idempotent unsubscribe function.
• emit(event, ...args) calls every listener synchronously and returns how many ran. Listeners are snapshotted first, so on / off from inside a listener take effect on the next emit.
• A listener exception does not abort the loop: remaining listeners still run and the first error is re-thrown afterwards (mirrors DOM EventTarget).
• off, clear(event?), and listenerCount(event) round out the surface.

Single-channel fan-out

For a one-event channel, createListeners is a lighter primitive: add returns an unsubscribe and emit(value) notifies all subscribers.

import { createListeners, type Listeners } from "@oh-just-another/events";

const channel: Listeners<number> = createListeners<number>();
const off = channel.add((n) => console.log(n));
channel.emit(42);
off();