Stateful2.js

define([
    'dojo/declare',
	'dojo/promise/when'
], function (declare, when) {
	var slice = [].slice,
		nop = function () {};

	function createNotifier(object) {
		var listenerMap = {},
			objectListeners = [];

		function notify(name, newValue, oldValue) {
			var listeners = listenerMap[name];
			if (listeners) {
				listeners.forEach(function (listener) {
					listener.handler.call(object, newValue, oldValue);
				});
			}
			objectListeners.forEach(function (listener) {
				listener.handler.call(object, name, newValue, oldValue);
			});
		}
		notify.register = function (property, listener) {
			var listeners = listenerMap[property];
			if (!listener && typeof property === 'function') {
				listener = property;
				listeners = objectListeners;
			}
			else {
				if (!listeners) {
					listeners = listenerMap[property] = [];
				}
			}
			listener = { handler: listener };
			listeners.push(listener);

			var handle = {
				remove: function () {
					var index = listeners.indexOf(listener);
					if (index > -1) {
						listeners.splice(index, 1);
					}
					handle.remove = nop;
				}
			};
			return handle;
		};
		return notify;
	}

	return declare(null, {
		postscript: function (params) {
			if (params) {
				this.set(params);
			}
		},
		_get: function (property) {
			return this[property];
		},
		get: function (property) {
			var getter = this['_get_' + property];
			if (typeof getter === 'function') {
				return getter.apply(this, slice.call(arguments, 1));
			}
			else {
				return this._get(property);
			}
		},
		_set: function (property, value) {
			var oldValue = this.get(property),
				result = this[property] = value;

			if (this.__notify && value !== oldValue) {
				var self = this;
				return when(result, function () {
					self.__notify(property, value, oldValue);
				});
			}
			return result;
		},
		set: function (property, value) {
			if (typeof property === 'object') {
				var results = {};
				for (var key in property) {
					results[key] = this.set(key, property[key]);
				}
				return results;
			}

			var setter = this['_set_' + property],
				result;
			if (typeof setter === 'function') {
				result = setter.apply(this, slice.call(arguments, 1));
			}
			else {
				result = this._set(property, value);
			}

			return result;
		},
		listen: function (property, listener) {
			var notify = this.__notify;
			if (!notify) {
				Object.defineProperty(this, '__notify', {
					configurable: false,
					enumerable: false,
					writable: false,
					value: notify = createNotifier(this)
				});
			}
			return notify.register(property, listener);
		}
	});
});