Sending and receiving events with EventEmitters

EventEmitters are one of the core idioms of Node.js. If Node.js's core idea is an event-driven architecture, emitting events from an object is one of the primary mechanisms of that architecture. An EventEmitter is an object that gives notifications—events—at different points in its life cycle. For example, an HTTP Server object emits events concerning each stage of the startup/shutdown of the Server object, and as HTTP requests are made from HTTP clients.

Many core Node.js modules are EventEmitters, and EventEmitters are an excellent skeleton to implement asynchronous programming. EventEmitters have nothing to do with web application development, but they are so much part of the Node.js woodwork that you may skip over their existence. 

In this chapter, we'll work with the HTTPServer and HTTPClient objects. Both are subclasses of the EventEmitter class, and rely on it to send events for each step of the HTTP protocol. 

JavaScript classes and class...