EventEmitter

Instances of this class can collect listeners and emit events. An instance is either directly instantiated by calling new EventEmitter or by inheritance from other class. If other classes inherit this class, they must call the EventEmitter constructor.

If the EventEmitter is called without as function (without new operator), it'll return new instance of EventEmitter.

Usage

var require('lee').EventEmitter;
var emitter = new EventEmitter;
var emitter2 = new EventEmitter();
var emitter3 = EventEmitter();
function MyEmitter() {
    EventEmitter.call(this);
}
MyEmitter.prototype = Object.create(EventEmitter.prototype);
var customEmitter = new MyEmitter();

Methods

Method(s)	Description
[[on	EventEmitter.addEventListener]], [[addListener
[[once	EventEmitter.once]]
[[off	EventEmitter.removeEventListener]], [[removeListener
[[hasListener	EventEmitter.hasListener]]
[[getSortedListenerList	EventEmitter.getSortedListenerList]]
[[getGroupedListenerList	EventEmitter.getGroupedListenerList]]
[[getListenerDependencyList	EventEmitter.getListenerDependencyList]]
[[emit	EventEmitter.emit]]
[[emitSeries	EventEmitter.emitSeries]]

Listeners

EventEmitter support three types of listeners.

• Listener added as dependency.
• Listener with self-remove (called once).
• Normal listener.

A listener is a function. Adding function twice have no effect unless it is promoted.

Listener promotion

A listener can be promoted after they have been added. However listeners cannot be demoted. Here is the order of promotion:

Listener as dependency

Let have following example:

var emitter = new EventEmitter();
var f = function() {}, g = function() {};
emitter.on("my-event", f, [g]); //1
emitter.once("my-event", g); //2

Both functions f and g will be added as listeners for "my-event", but after (1) f is added explicitly, while g is added as dependency of f. Removing f will also remove g (unless other listener functions for this event depend on g).

After (2) however g is promoted to a listener with self-removal. If won't be removed if f is removed.

Listener with self-removal

Let have following example:

var emitter = new EventEmitter();
var f = function() {};
emitter.once("my-event", f); //1
emitter.on("my-event", f); //2

After (1) f is added as listener with self-removal. However after (2) f is promoted to normal listener and it won't be removed after the call.

Normal listener

Normal listeners stays until they are removed or EventEmitter instance has been garbage collected.