event-bus-lite

A lightweight, zero-dependency event bus for Node.js with wildcard subscriptions, async handler support, once listeners, middleware chain, event history, and clean unsubscribe API.

Installation

npm install event-bus-lites

Quick Start

const { EventBus } = require('event-bus-lites');
const bus = new EventBus();

bus.on('user.created', (payload) => {
  console.log('New user:', payload.name);
});

bus.emit('user.created', { name: 'John' });

Features & Usage

Wildcard Subscriptions

bus.on('user.*', (payload, event) => {
  console.log(`Event: ${event}`, payload);
});

bus.emit('user.created', { id: 1 });  // ✅ matches
bus.emit('user.updated', { id: 1 });  // ✅ matches
bus.emit('order.created', { id: 1 }); // ❌ no match

// Deep wildcard
bus.on('**', (payload, event) => {
  console.log('Any event:', event);
});

Once Listeners

bus.once('app.ready', () => console.log('Ready!'));
bus.emit('app.ready'); // fires
bus.emit('app.ready'); // nothing happens

Async Handlers

bus.on('order.placed', async (order) => {
  await sendEmail(order.email);
  await updateInventory(order.items);
});

await bus.emit('order.placed', order); // waits for all handlers

Unsubscribe

const unsub = bus.on('tick', () => console.log('tick'));
unsub(); // removes this specific listener

Middleware

bus.use((event, payload, next) => {
  console.log(`[LOG] ${event}`);
  next(); // continue — don't call next() to block the event
});

Event History

bus.enableHistory(50);
bus.emit('user.login', { id: 1 });
console.log(bus.getHistory());

API

| Method | Description | |---|---| | on(event, handler) | Subscribe (returns unsubscribe fn) | | once(event, handler) | Subscribe once | | emit(event, payload) | Emit event (async, returns Promise) | | off(event?) | Remove listeners (all if no event) | | use(middleware) | Add middleware | | listenerCount(event) | Count listeners for event | | eventNames() | List registered event names | | enableHistory(max) | Enable event logging | | getHistory() | Get event history | | clearHistory() | Clear history |

License

MIT