Simple Observer Pattern Framework for Nodejs

Completely untested! Completely for fun and learning experience.

Notifier Class

• Handles registration of listeners
• Emitting events to listeners
• Each 'Subject or Observed Class' must implement a property called notifier that is of type new Notifier()

Events Class ( Global / Singleton )

• Retains an index of all Events available to the program
• Handles registration of events
• Ensures that each registered inherits from Event to ensure consistency
• Provides a factory that creates new instances of events
• Provides an index of Event names for observers to use when registering instead of string literals

EventHandlers

• Each Observer should implement a property that is of type new EventHandlers()
• Ensures that only Events inheriting from EventHandler are allowed in the registry.. ensuring consistency
• When registering to listen to a Subject it must use the following syntax: subject.on(EventName, observer.eventHandlers)
• Implements a onNotify() which selects the corresponding EventHandler based on the Event recieved
• Implements an EventHandler factory that creates a new instance of the EventHandler passing in the event and a 'this' reference to the observer
• onNotify() then calls resolve() on the EventHandler (Polymorphism allows custom behaviour for each handler)

EventHandler

• A base class with properties to store a reference to the event and the observer
• abstract resolve() method that should be overridden by the custom Handler subclass

Event

• A base class with properties for name which is derived from the class name and used by notifier
• A property for data which the payload from the event broadcast
• An optional property 'invoker' which can be used to print the name of the broadcaster