   #
   # Returns a {Disposable} on which `.dispose()` can be called to unsubscribe.
   on: (eventName, handler, unshift=false) ->
-    if @isDisposed
+    if @disposed
       throw new Error("Emitter has been disposed")
 
     if typeof handler isnt 'function'

# ```
module.exports =
class Emitter
  isDisposed: false

  ###
  Section: Construction and Destruction

  # Public: Unsubscribe all handlers.
  dispose: ->
    @handlersByEventName = null
    @disposed = true

  ###
  Section: Event Subscription
