Event Multiplexer

If you ever had to register or de-register listeners in bulk and resorted to using arrays, sets, maps and dictionaries to achieve it; This library will take that responsibility off your shoulders.

This is useful for example in a game or user generated graphics application (which was the original motivation behind this library).

Features:

• Listen on multiple event emitters
• Automatic listening to existing listeners after adding to multiplexer
• Automatic listener removal after removal from multiplexer
• Multiplexer events

Installation

If you're here, you already know.

npm install --save event-multiplexer

or

yarn add event-multiplexer

Usage

The EventMultiplexer is also itself an implementation of EventEmitter hence any calls to on, off, addListener, removeListener

The new additions are add(...objects) and remove(...objects) for adding and removing emitters from the multiplexer.

Initialize

First create the multiplexer.

// Import the `EventMultiplexer` class
import { EventMultiplexer } from  'event-multiplexer';
 
// Initialize a multiplexer instance.
const  mux  =  new EventMultiplexer();

Let's make a few test emitters.

// This is for demo purposes, any emitter or
// child implementation will work.
import { EventEmitter } from 'events';
 
// Our Test objects.
const  obj_a = new EventEmitter();
obj_a.name = "Apple";
 
const  obj_b = new EventEmitter();
obj_b.name = "Bose";
 
const  obj_c  =  new EventEmitter();
obj_c.name = "Cisco";
 
const  obj_d  =  new EventEmitter();
obj_d.name  =  "Dell";

add(...objects) to the MUX

Complexity:

• O(n*m) where n = |objects| and m = |distinct events being listened to|

Add the objects to the mux

// You can add objects before you add listeners
mux.add(obj_a);
 
// This is a listener (lol duh)
// More on this later.
mux.on('EVENT', () => {
    console.log("I like trains.");
});
 
// ... and add objects after you add listeners.
mux.add(obj_b);
 
// ... or add multiple wherever
mux.add(obj_b, obj_c, obj_d);

Don't worry about repeating add operations, it will only listen on the object once.

Listen on the MUX

Add listeners on the mux and wait!

mux.on('HELLO', (object, greeting, ...args) => {
    // The first argument to a handler is always the object
    // producing the event.
    console.log(`${object.name} says: ${greeting}`);
});
 
// We have added the objects to the mux before.
obj_d.emit('HELLO', 'Bonjour');
obj_a.emit('HELLO', 'Salam');
obj_c.emit('HELLO', 'Namaste');

The above will produce the output

Dell says: Bonjour
Apple says: Salam
Cisco says: Namaste

remove(...objects) from the MUX

Complexity:

• O(n*m) where n = |objects| and m = |distinct events being listened to|

const  handler  = () => {}
mux.on('EVENT', handler);
 
// Remove.
mux.off('EVENT', handler);

MUX without the object being passed.

const mux = new EventMultiplexer(false);
mux.on('EVENT', (...args) => {});

The first argument to the constructor configures it to pass (on default true) or alternatively not pass (on false) the object producing the event to the event handlers.

Events

The library also exports OBJECT_ADDED and OBJECT_REMOVED symbols. These can be used to listen for object changes on the multiplexer.

import {
    OBJECT_ADDED,
    OBJECT_REMOVE,
    EventMultiplexer
} from `event-multiplexer`;
 
const obj_a = {name: "A"};
const obj_b = {name: "B"};
 
const mux = new EventMultiplexer();
 
mux.on(OBJECT_ADDED, (object) => {
    console.log(`${object.name} added.`);
});
 
mux.on(OBJECT_REMOVED, (object) => {
    console.log(`${object.name} removed.`);
});
 
mux.add(obj_a, obj_b);
mux.remove(obj_a);

will produce

A added.
B added.
A removed.

Requirements

Any event emitter implementation that had the on(name, listener) and off(name, listener) methods that work similar to node's implementation should work.

Internally it uses the EventEmitter export from the environment provided events module. That means you will need so setup your packager to provide that module.

Webpack provides this by default.

License

MIT