Overview
The Emitter class provides a simple and efficient event emitter implementation for the publish-subscribe pattern. It allows you to register event listeners, emit events, and manage subscriptions.
Class: Emitter
Constructor
const emitter = new Emitter();
Methods
on()
Registers an event listener for the specified event.
on<Args extends unknown[]>(event: string, callback: Callback<Args>): () => void
The name of the event to listen for
The callback function to execute when the event is emitted. The callback receives the arguments passed to emit().
Returns an unsubscribe function that removes the listener when called
const unsubscribe = emitter.on('user:created', (user) => {
console.log('User created:', user);
});
// Later, to remove the listener
unsubscribe();
off()
Removes a specific event listener.
off<Args extends unknown[]>(event: string, callback: Callback<Args>): void
The callback function to remove
const handler = (data) => console.log(data);
emitter.on('data:update', handler);
// Remove the specific listener
emitter.off('data:update', handler);
offAll()
Removes all listeners for a specific event, or all listeners for all events.
offAll(event?: string): void
The name of the event to clear. If omitted, clears all listeners for all events.
// Remove all listeners for a specific event
emitter.offAll('user:created');
// Remove all listeners for all events
emitter.offAll();
once()
Registers a one-time event listener that automatically unsubscribes after being called once.
once<Args extends unknown[]>(event: string, callback: Callback<Args>): void
The name of the event to listen for
The callback function to execute once when the event is emitted
emitter.once('app:ready', () => {
console.log('Application is ready!');
});
emitter.emit('app:ready'); // Logs: "Application is ready!"
emitter.emit('app:ready'); // Does nothing - listener was removed
emit()
Emits an event synchronously, calling all registered listeners immediately.
emit<Args extends unknown[]>(event: string, ...args: Args): void
The name of the event to emit
Arguments to pass to the event listeners
emitter.emit('user:created', { id: 1, name: 'John' });
emitter.emit('data:processed', 'result', 42, true);
emitAsync()
Emits an event asynchronously, calling all registered listeners in the next microtask.
emitAsync<Args extends unknown[]>(event: string, ...args: Args): void
The name of the event to emit
Arguments to pass to the event listeners
emitter.emitAsync('background:task', taskData);
console.log('This logs first');
// The event listeners will be called in the next microtask
Type Definitions
Callback
type Callback<Args extends unknown[] = unknown[]> = (...args: Args) => void;
Usage Example
import { Emitter } from '@resolid/event';
const emitter = new Emitter();
// Register event listeners
const unsubscribe = emitter.on('user:login', (user) => {
console.log(`User ${user.name} logged in`);
});
emitter.on('user:login', (user) => {
console.log(`Welcome back, ${user.name}!`);
});
// Emit an event
emitter.emit('user:login', { name: 'Alice', id: 1 });
// Logs:
// "User Alice logged in"
// "Welcome back, Alice!"
// One-time listener
emitter.once('app:initialized', () => {
console.log('App initialized!');
});
// Unsubscribe
unsubscribe();
// Clear all listeners for an event
emitter.offAll('user:login');
Source Code
Location: packages/event/src/index.ts