Eonemitter

A minimal, fully-typed, and reactive event emitter for TypeScript and JavaScript.

This lightweight utility provides a simple yet powerful mechanism for handling events in a reactive style. It offers a fully type-safe API, supports multiple listeners, and integrates cleanly with observable patterns without any external dependencies.

✅ Features

• ✅ EventEmitter – basic event system for emitting and listening to events
• ✅ BehaviorEventEmitter – like BehaviorSubject, emits the last value to new subscribers
• ✅ Fully typed and lightweight

📦 Installation

npm install eonemitter

🚀 Quick Start

ES Modules

import { EventEmitter, BehaviorEventEmitter } from 'eonemitter';

// Basic EventEmitter
const emitter = new EventEmitter<string>();

const subscription = emitter.subscribe((value) => {
  console.log(value); // Logs: 'Hello!'
});

emitter.emit('Hello!');
subscription.unsubscribe();

// BehaviorEventEmitter emits the latest value to new subscribers
const behaviorEmitter = new BehaviorEventEmitter<number>();

const subscription2 = behaviorEmitter.subscribe((value) => {
  console.log(value); // Logs: 777 repeatedly
});

setInterval(() => behaviorEmitter.emit(777), 100);
setTimeout(() => subscription2.unsubscribe(), 500);

CommonJS

const { EventEmitter } = require('eonemitter');

const emitter = new EventEmitter<string>();
emitter.subscribe((value) => {
  console.log(value);
});

emitter.emit('Hi from CommonJS!');

📚 API

EventEmitter

EventEmitter - a generic event emitter that allows subscribing to and emitting events of type T. Supports multiple subscribers and provides control over subscription lifecycles.

subscribe(callback: (value: T) => void): ISubscription
// Subscribes to all future events

subscribeOnce(callback: (value: T) => void): ISubscription
// Subscribes to only the next event, then automatically unsubscribes

asObservable(): IObservable<T> 
// Returns a read-only observable interface to this emitter.

hasSubscribers(): boolean
// Returns true if there are any active subscribers.

emit(value: T): void
// Emits a new event to all current subscribers

unsubscribeAll(): void
// Removes all active subscribers

BehaviorEventEmitter

BehaviorEventEmitter - extends EventEmitter by storing the most recent value. New subscribers will immediately receive the last emitted value upon subscribing.

getValue(): T
// Returns the most recently emitted value.

IObservable

IObservable - exposes a interface for subscribing to events

subscribe(callback: (value: T) => void): ISubscription
// Subscribes to all future events.

subscribeOnce(callback: (value: T) => void): ISubscription
// Subscribes to the next emitted event only, then automatically unsubscribes.

ISubscription

ISubscription - represents a subscription to an event stream. Used to manually unsubscribe when needed.

  unsubscribe(): void; 
  // Cancels the subscription.