A simple factory which returns a Pub/Sub style Event Emitter in ES6. Subscription is managed via the addListener (reusable events) or the once methods to add a new listener to a given event name. Individual handlers are removed via the returned unsubscribe function, or by using the removeListener method (both remove the first matching handler function for that event type). Handlers registered by the "once" method can only be removed using their returned unsubscribe function. The removeAllListeners method clears all registered listeners for the given event name, but does not remove the event name from the registered events. Events are emitted using the emit method, and the handlers are called in the order they were registered for a given event name, minus any listeners that were removed before an emit event occurred. Emitting an event for an emptied event name does not throw an error.

Adds a new listener for the event based on the string token eventName, or creates the event type if not in dict of events. Throws a TypeError if not passed a callback function.

Parameters

eventName: string, A string token for event type, by name

cb: function, The callback function to invoke when a matching event is emitted

Adds a one-time-use listener for the eventName, removed from listeners after first matching event is emitted. Cannot be removed by removeListener - must use the returned unsubscribe function. Throws a TypeError if not passed a function as a handler.

Parameters

eventName: string, A string token for event type, by name

cb: function, The callback function to invoke once when a matching event is emitted

When an event is emitted matching a registered event type, invokes each listener's callback function in the order they were registered, passing along whatever arguments the emit method recieved. Throws a ReferenceError if the event name has never been registered - passes silently if no handlers are currently registered for a given event name.

Parameters

eventName: string, A string token for event type, by name

args: *, Takes any number of any type of arguments and passes them to the callback functions

Removes the first matching listener for the event based on the string token eventName. Returns true if a matching callback is found, throws a ReferenceError if no events are registered by the event name or no matching listeners are found.

Parameters

eventName: string, A string token for event type, by name

cb: function, The callback function to remove from the registered listeners

Removes all matching listeners for the event based on the string token eventName. Returns the EventEmitter if a matching event name is found, throws a ReferenceError if no events are registered by the event name. Note: does not remove the event type key from the dict, simply clears all listeners.

Parameters

eventName: string, A string token for event type, by name, to remove all events.