event-emitter-joint

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. You may provide the constructor with a broadcaster or an array of broadcasters.

Extra methods:

• addBroadcaster()
• addBroadcasters([])
• removeBroadcaster([], 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([], keepListeners)

Usage

npm install 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.

License

MIT