A lightweight publish/subscribe event system. Listeners register with on(), fire once with once(), are removed with off(), and events are dispatched with emit(). Useful for decoupling modules, building plugin systems, and implementing the Observer pattern without a framework dependency.
JavaScript
class EventEmitter {
#events = {};
on(event, listener) {
(this.#events[event] ??= []).push(listener);
return () => this.off(event, listener);
}
once(event, listener) {
const wrapper = (...args) => { listener(...args); this.off(event, wrapper); };
return this.on(event, wrapper);
}
off(event, listener) {
this.#events[event] = (this.#events[event] ?? []).filter((l) => l !== listener);
}
emit(event, ...args) {
(this.#events[event] ?? []).forEach((l) => l(...args));
}
}
// Usage
const bus = new EventEmitter();
const off = bus.on('data', (d) => console.log('received:', d));
bus.emit('data', { id: 1 }); // received: { id: 1 }
off(); // unsubscribeSave your own code snippets
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