What is the difference between addListener(event, listener) and on(event, listener) method in node.js?

Question

Here i cannot understand what is the basic difference between these two methods.

var events = require(\'events\');
var eventEmitter = new events.EventEmitter         


        

Answer 1

Their functionalities are exactly the same, however, they can be used in different ways to make your code efficient. Lets assume you created a server and you create a listener, by using ".addListener(event, listener)", for every user that connects to your server. Now as soon as a user is disconnected, you can remove that listener by using the command "removeListener", but you cannot remove the ".on(event, listener)" command. So, you can use these two commands for different situations.

Answer 2

Yes you can use "removeListener" with with a listener created with "on". Try it.

var events = require('events');
var eventEmitter = new events.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', listner2);
console.log("Listner2 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.");

Answer 3

Added in: v10.0.0

emitter.off(eventName, listener)

Alias for emitter.removeListener()

Answer 4

.on() is exactly the same as .addListener() in the EventEmitter object.

Straight from the EventEmitter source code:

EventEmitter.prototype.on = EventEmitter.prototype.addListener;

Sleuthing through the GitHub repository, there is this checkin from Jul 3, 2010 that contains the comment: "Experimental: 'on' as alias to 'addListener'".

---

Update in 2017: The documentation for EventEmitter.prototype.addListener() now says this:

Alias for emitter.on(eventName, listener).