Generic implementation of EventEmitter for browser in CoffeeScript

EventEmitter.coffee

class EventEmitter
    on: (name, listener) ->
        listeners = (@_eventListeners ?= {})[name] ?= []
        listeners.push listener

    off: (name, listener) ->
        if listeners = @_eventListeners?[name]
            index = listeners.indexOf listener
            listeners[index] = null if index >= 0

    emit: (name) ->
        if listeners = @_eventListeners?[name]
            args = Array.prototype.slice.call arguments, 1
            listener?.apply @, args for listener in listeners
        
    once: (name, listener) ->
        remover = =>
            @off name, listener
            @off name, remover
        @on name, listener
        @on name, remover

    addEventListener: @::on
    removeEventListener: @::off