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

.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).

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.");