EventEmitter.md

EventEmitter

Priority-aware async event emitter built on TaskQueue.

Import

import { EventEmitter } from '@stackpress/lib';

When To Use It

Use EventEmitter when your event names are exact strings and you want ordered async listeners, before/after hooks, and status results instead of fire-and-forget callbacks.

API

Constructor

type Events = {
  'user.created': [string];
  'user.deleted': [string, boolean];
};

const emitter = new EventEmitter<Events>();

Properties

Name	Type	Notes
after	EventHook<M[keyof M]>	Runs after each task. Returning false aborts the queue.
before	EventHook<M[keyof M]>	Runs before each task. Returning false aborts the queue.
event	current Event	Metadata for the task being executed.
listeners	frozen shallow copy	Raw listener registry keyed by event name.

Methods

Method	Returns	Notes
clear(event)	this	Removes all listeners for one event.
emit(event, ...args)	Promise<ResponseStatus>	Returns Status.NOT_FOUND, Status.ABORT, or Status.OK.
makeQueue()	TaskQueue	Overridable queue factory.
match(event)	Map<string, EventMatch>	Exact-match lookup in the base class.
on(event, action, priority = 0)	this	Adds a listener. Higher priority runs first.
tasks(event)	TaskQueue	Materializes the matching listeners into a queue.
unbind(event, action)	this	Removes one listener function.
use(emitter)	this	Merges listeners from another emitter.

Example

import { EventEmitter } from '@stackpress/lib';

type Events = {
  saved: [string];
};

const emitter = new EventEmitter<Events>();

emitter.before = async event => {
  console.log('before', event.event);
};

emitter.on('saved', async id => {
  console.log('saved', id);
}, 10);

await emitter.emit('saved', 'abc123');

Related

• ExpressEmitter
• TaskQueue
• Status