EventEmitterJoint

control any number of underlying event emitters ("broadcasters") via a central joint
cascade events over chains of event emitters
dynamically add/remove broadcasters just like you would do with listeners
extends the standard EventEmitter retaining its interface
no overhead during events emission

How it works

Internally the joint is listening for newListener/removeListener events and adds/removes the listener that caused them to/from broadcasters.

Note:

It's not the events that propagate up the chain, rather the addition and removal of listeners propagates down. When a listener is added to a joint, it's propagated down the joints chain to the base joint or non-joint event emitter. When an event is emitted from the base event emitter the listener is triggered directly, thus there's no overhead implied by the chain.
There's currently no way to add a listener to the joint without adding the same listener to the underlying broadcasters, nor I know why anyone would want to do this.

API

The interface is inherited from native EventEmitter.

Extra methods:

constructor(broadcasters) - provide the constructor with a broadcaster or an array thereof
addBroadcaster(EventEmitter ee)
addBroadcasters([EventEmitter ee])
removeBroadcaster(EventEmitter ee, bool keepListeners)) - when removing a broadcaster, set keepListeners to true if you want to keep listening to the broadcaster after removal. Does not sound safe or consistent but could find its purpose.
removeBroadcasters([EventEmitter ee], bool keepListeners)
getBroadcasters() - returns a copy of the list of broadcasters.

Events

newBroadcaster - like newListener, fired when broadcaster is added, the listener receives the broadcaster as first argument
removeBroadcaster - like removeListener, see above

Usage

npm install --save event-emitter-joint

Then

const 
	EventEmitterJoint = require('event-emitter-joint'),
	EventEmitter = require('events');

const
	a = new EventEmitter(),
	b = new EventEmitter(),
	c = new EventEmitter(),
	x = new EventEmitterJoint([a,b]),
	listener = (txt) => console.log("listener 1: " + txt),
	listener2 = (txt) => console.log("listener 2: " + txt);

x.on('test', listener);

a.emit('test', 'this is emitted from a and delivered via x')
b.emit('test', 'for the sake of completeness, this is emitted from b and delivered via x')    

x.addBroadcaster(c)

c.emit('test', 'this is emitted from с which was added after instantiation and delivered via x')

x.removeBroadcaster(b)

b.emit('test', 'this is not going anywhere because b was removed from x')

x.addBroadcaster(b)

b.emit('test', 'this is emitted from b after reconnecting it as a broadcaster')

You'll find a chaining example in test directory.

Todo

Automate tests
Add custom base class to support usage in browsers

Contributing

Open an issue or make a pull request.

Changelog:

Mar 29, 2018 v0.9.3:

emitting newBroadcaster/removeBroadcaster events
.getBroadcasters() returns a reference to a copy of the internal _broadcasters property
addBroadcaster(s) now makes sure the broadcaster is not added more than once using plain object equality

Mar 15, 2018 v0.9.1:

All basic features implemented

License

MIT

License

IgorRubinovich/event-emitter-joint

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