object-watch.coffee

/*
 * object.watch polyfill
 *
 * 2014-08-23
 *
 * By [email protected]
 *
 * Usage:
 * obj.watch('a', (name, old, new) -> console.log "#{name} changed from #{old} to #{new}"
 *
 * Public Domain.
 * NO WARRANTY EXPRESSED OR IMPLIED. USE AT YOUR OWN RISK.
 */

#  object.watch
    unless Object::watch?  
      Object.defineProperty Object::, "watch",
        enumerable: false, configurable: true, writeable: false, value: (prop, handler) ->
          oldval = @[prop]
          newval = oldval
          getter = () -> newval
          setter = (val) -> oldval = newval; newval = handler.call(@, prop, oldval, val)
          Object.defineProperty @, prop, get: getter, set: setter, enumerable: true, configurable: true if delete @[prop]

    unless Object::unwatch?
      Object.defineProperty Object::, "unwatch",
        enumerable: false, configurable: true, writeable: false, value: (prop) ->
          prop = @[prop]
          delete @[prop]
          @[prop] = val

object-watch in coffee

In unwatch:
prop = @[prop] should be
val = @[prop]
because val is not been set otherwise.