simple object observer

obs.coffee

Object.defineProperty Object::, "__obs",
  enumerable: false
  configurable: true
  writable: false
  value: (prop, handler) ->
    val = this[prop]

    if delete this[prop] # can't watch constants
      Object.defineProperty this, prop,
        get: ->
          val
        set: (newVal) ->
          val = newVal
          handler.call(this, prop)
        enumerable: true
        configurable: true

Object.defineProperty Object::, "__unobs",
  enumerable: false
  configurable: true
  writable: false
  value: (prop) ->
    val = this[prop]
    delete this[prop] # remove accessors

    this[prop] = val