Module pattern in Coffeescript

collection.coffee

class MyCollection extends Backbone.Collection
  classExtend(@, ModuleCollectionAsOptions)
  
# works
new MyCollection().toOptionsJSON()

extend.coffee

window.classExtend = (klass, module) ->
  _.extend(klass.prototype, module.prototype)

module.coffee

class ModuleCollectionAsOptions
  toOptionsJSON: (textAttribute="title")->
    @map (model) ->
      value: model.id
      text: model.get(textAttribute)