TJ's EventEmitter in CoffeeScript

Emitter.coffee

###
Initialize a new `Emitter`.

@api public
###
module.exports = Emitter = (obj) ->
  return mixin(obj) if obj
  @_callbacks = {}

###
Mixin the emitter properties.

@param {Object} obj
@return {Object}
@api private
###
mixin = (obj) ->
  obj._callbacks = {}
  for key of Emitter.prototype
    obj[key] = Emitter::[key]
  obj

###
Listen on the given `event` with `fn`.

@param {String} event
@param {Function} fn
@return {Emitter}
@api public
###
Emitter::on = (event, fn) ->
  (@_callbacks[event] or= []).push fn
  this


###
Adds an `event` listener that will be invoked a single
time then automatically removed.

@param {String} event
@param {Function} fn
@return {Emitter}
@api public
###
Emitter::once = (event, fn) ->
  once = =>
    @off event, once
    fn.apply this, arguments
  fn._off = once
  @on event, once


###
Remove the given callback for `event` or all
registered callbacks.

@param {String} event
@param {Function} fn
@return {Emitter}
@api public
###
Emitter::off = (event, fn) ->
  callbacks = @_callbacks[event]
  return this unless callbacks

  # remove all handlers
  if 1 is arguments.length
    delete @_callbacks[event]
    return this

  # remove specific handler
  i = callbacks.indexOf(fn._off or fn)
  callbacks.splice i, 1 if ~i
  this


###
Emit `event` with the given args.

@param {String} event
@param {Mixed} ...
@return {Emitter}
###
Emitter::emit = (event, args...) ->
  callbacks = @_callbacks[event]
  if callbacks
    for callback in callbacks.slice 0
      callback.apply(this, args)
  this


###
Return array of callbacks for `event`.

@param {String} event
@return {Array}
@api public
###
Emitter::listeners = (event) ->
  @_callbacks[event] or []


###
Check if this emitter has `event` handlers.

@param {String} event
@return {Boolean}
@api public
###
Emitter::hasListeners = (event) ->
  !! @listeners(event).length

Emitter.js

/**
 * Expose `Emitter`.
 */

module.exports = Emitter;

/**
 * Initialize a new `Emitter`.
 * 
 * @api public
 */

function Emitter(obj) {
  if (obj) return mixin(obj);
  this._callbacks = {};
};

/**
 * Mixin the emitter properties.
 *
 * @param {Object} obj
 * @return {Object}
 * @api private
 */

function mixin(obj) {
  obj._callbacks = {};
  for (var key in Emitter.prototype) {
    obj[key] = Emitter.prototype[key];
  }
  return obj;
}

/**
 * Listen on the given `event` with `fn`.
 *
 * @param {String} event
 * @param {Function} fn
 * @return {Emitter}
 * @api public
 */

Emitter.prototype.on = function(event, fn){
  (this._callbacks[event] = this._callbacks[event] || [])
    .push(fn);
  return this;
};

/**
 * Adds an `event` listener that will be invoked a single
 * time then automatically removed.
 *
 * @param {String} event
 * @param {Function} fn
 * @return {Emitter}
 * @api public
 */

Emitter.prototype.once = function(event, fn){
  var self = this;

  function on() {
    self.off(event, on);
    fn.apply(this, arguments);
  }

  fn._off = on;
  this.on(event, on);
  return this;
};

/**
 * Remove the given callback for `event` or all
 * registered callbacks.
 *
 * @param {String} event
 * @param {Function} fn
 * @return {Emitter}
 * @api public
 */

Emitter.prototype.off = function(event, fn){
  var callbacks = this._callbacks[event];
  if (!callbacks) return this;

  // remove all handlers
  if (1 == arguments.length) {
    delete this._callbacks[event];
    return this;
  }

  // remove specific handler
  var i = callbacks.indexOf(fn._off || fn);
  if (~i) callbacks.splice(i, 1);
  return this;
};

/**
 * Emit `event` with the given args.
 *
 * @param {String} event
 * @param {Mixed} ...
 * @return {Emitter} 
 */

Emitter.prototype.emit = function(event){
  var args = [].slice.call(arguments, 1)
    , callbacks = this._callbacks[event];

  if (callbacks) {
    callbacks = callbacks.slice(0);
    for (var i = 0, len = callbacks.length; i < len; ++i) {
      callbacks[i].apply(this, args);
    }
  }

  return this;
};

/**
 * Return array of callbacks for `event`.
 *
 * @param {String} event
 * @return {Array}
 * @api public
 */

Emitter.prototype.listeners = function(event){
  return this._callbacks[event] || [];
};

/**
 * Check if this emitter has `event` handlers.
 *
 * @param {String} event
 * @return {Boolean}
 * @api public
 */

Emitter.prototype.hasListeners = function(event){
  return !! this.listeners(event).length;
};