Node.js event emitter explained

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Node.js core API is based on asynchronous event-driven architecture in which certain kind of objects called emitters periodically emit events that cause listener objects to be called.

All objects that emit events are members of EventEmitter class. These objects expose an eventEmitter.on() function that allows one or more functions to be attached to named events emitted by the object.

When the EventEmitter object emits an event, all of the functions attached to that specific event are called synchronously. All values returned by the called listeners are ignored and will be discarded.

Consider the following example:

const EventEmitter = require('events');
class MyEmitter extends EventEmitter {}
const myEmitter = new MyEmitter();
myEmitter.on('event', function(a, b) {
  console.log(a, b, this);
  // Prints:
  //   Technoetics Club MyEmitter {
  //     domain: null,
  //     _events: { event: [Function] },
  //     _eventsCount: 1,
  //     _maxListeners: undefined }
});
myEmitter.emit('event','Technoetics', 'Club');

Here we create a myEmitter object and emit event at the end which triggers the callback function and we are able to get the desired output.

By default, all listeners attached to a particular event object are called by the EventListener object…