observers in coffeescript

observers.coffee

_watch = (prop, fn) ->
  subs[prop] = []  unless subs[prop]
  subs[prop].push fn

_notify = (prop, val) ->
  if subs[prop]
    subs[prop].forEach (cb) ->
      cb val

_compare = (a, b) ->
  JSON.stringify(a) is JSON.stringify(b)

_change = (prop, val) ->
  unless _compare(val, save[prop])
    save[prop] = val
    _notify prop, val