CoffeScript event emitter

emitter.coffee

class Emitter
   constructor: ->
     @events = {}
   on: (e, cb)->
     @events[e] = [] unless @events[e]
     @events[e].push cb
     this
   off: (e, cb)->
        unless cb
          @events[e] = []
        else
          index = @events[e].indexOf cb
          @events[e].splice index, 1
   emit: ->
       args = Array.prototype.slice.call arguments
       e = args.shift()
       self = this
       @events[e].forEach (cb)->
         cb.apply self, args
       this