decorator-events

Extremely fast decorator-based event library.

This library builds a function that handles all events each time EventBus::register is called. This function is made to be easily optimized by Javascript engines, making this event library faster than native EventEmitters. Note that a big disadvantage to this approach is that registering is expensive (and unregistering is intentionally not made possible).

Event inheritance, event handler prioritization, and cancelling events is supported.

Inspired by the Spigot Event API.

Example

import { EventPriority, Event, EventHandler, EventBus } from 'decorator-events';

class SignInEvent extends Event {
  public sessionId?: string;

  constructor (public username: string, public password: string) {
    super();
  }
}

class SignInListener {
  @EventHandler
  async handleSignIn(event: SignInEvent): void {
    if (await passwordIsValid(event.username, event.password)) {
      event.sessionId = await createSessionIdForUser(event.username);
    } else {
      event.cancel();
    }
  }

  @EventHandler({ priority: EventPriority.MONITOR })
  logSignIn(event: SignInEvent): void {
    console.log(`User ${event.username} signed in!`);
  }


  @EventHandler({
    /* When to execute this handler.
     * Higher priority means later execution (thus more control over the final state of an event).
     * Defaults to EventPriority.NORMAL.
     */
    priority: EventPriority.NORMAL,
    /* Whether or not to ignore to cancelled events.
     * Defaults to false.
     */
    ignoreCancelled: true,
    /* Whether or not the override an event handler with the same name in a superclass.
     * Defaults to true. False means both methods are used.
     */
    override: false,
    /* Whether or not to listen to superclasses of the event being listened to.
     * Defaults to false.
     */
    inheritance: false,
  })
  showingOffSettings(event: Event): void {
    // ...
  }
}

const bus = new EventBus();
bus.register(new SignInListener());

await bus.emit(new SignInEvent('tim', 'password123')); // User Tim signed in!