Node.js - Event Emitter

Node.js - Event Emitter

EventEmitter Class

As we saw in the previous section, the EventEmitter class lies within the module for events. Accessible via the following code –

// Import events module
var events = require('events');
// Create an eventEmitter object
var eventEmitter = new events.EventEmitter();

When an instance of EventEmitter faces some mistake, it will emit a 'error' event. When a new listener is added, the event 'newListener' is fired, and the event 'removeListener' is fired when a listener is removed.

EventEmitter gives several properties such as on and emit. Binding feature to an event is used on the property and emitting is used to fire an event.

Class Methods

Events

Make a js file named main.js with the following code − Node.js

var events1 = require('events');
var eventEmitter = new events1.EventEmitter();
// listener #1
var listner1 = function listner1() {
   console.log('listner1 executed.');
}
// listener #2
var listner2 = function listner2() {
   console.log('listner2 executed.');
}
// Bind the connection event with the listner1 function
eventEmitter.addListener('connection', listner1);
// Bind the connection event with the listner2 function
eventEmitter.on('connection', listner2);
var eventListeners = require('events').EventEmitter.listenerCount
   (eventEmitter,'connection');
console.log(eventListeners + " Listner(s) listening to connection event");
// Fire the connection event 
eventEmitter.emit('connection');
// Remove the binding of listner1 function
eventEmitter.removeListener('connection', listner1);
console.log("Listner1 will not listen now.");
// Fire the connection event 
eventEmitter.emit('connection');
eventListeners = require('events').EventEmitter.listenerCount(eventEmitter,'connection');
console.log(eventListeners + " Listner(s) listening to connection event");
console.log("Program Ended.");

$ node main.js