Clean version of Flux Dispatcher

Dispatcher.js

/**
 * Copyright (c) 2014-2015, Facebook, Inc.
 * All rights reserved.
 *
 * This source code is licensed under the BSD-style license found in 
 * https://github.com/facebook/flux/blob/master/LICENSE. An additional grant
 * of patent rights can be found in the PATENTS file in the same directory.
 *
 */

define(function (require) {
    "use strict";

	var Dispatcher = {
		callbacks: {},
		isDispatching: false,
		isHandled: {},
		isPending: {},
		pendingAction: null,
		lastID: 1,

		register: function (callback) {
			var id = 'ID_' + this.lastID++;
			this.callbacks[id] = callback;
			return id;
		},

		unregister: function (id) {
			if (!this.callbacks[id]) {
				throw new Error('Dispatcher.unregister(...): ' + id + ' does not map to a registered callback. ');
			}
			delete this.callbacks[id];
		},

		waitFor: function (ids) {
			if (!this.isDispatching) {
				throw new Error('Dispatcher.waitFor(...): Must be invoked while dispatching.');
			}
			for (var ii = 0; ii < ids.length; ii++) {
				var id = ids[ii];
				if (this.isPending[id]) {
					if (!this.isHandled[id]) {
						throw new Error('Dispatcher.waitFor(...): Circular dependency detected while waiting for ' + id);
					}
					continue;
				}
				if (!this.callbacks[id]) {
					throw new Error('Dispatcher.waitFor(...): ' + id + ' does not map to a registered callback. ');
				}
				this.invokeCallback(id);
			}
		},

		dispatch: function (action) {
			if (this.isDispatching) {
				throw new Error('Dispatch.dispatch(...): Cannot dispatch in the middle of a dispatch.');
			}

			this.startDispatching(action);

			try {
				for (var id in this.callbacks) {
					if (this.isPending[id]) {
						continue;
					}
					this.invokeCallback(id);
				}
			} finally {
				this.stopDispatching();
			}
		},

		invokeCallback: function (id) {
			this.isPending[id] = true;
			this.callbacks[id](this.pendingAction);
			this.isHandled[id] = true;
		},

		startDispatching: function (action) {
			for (var id in this.callbacks) {
				this.isPending[id] = false;
				this.isHandled[id] = false;
			}
			this.pendingAction = action;
			this.isDispatching = true;
		},

		stopDispatching: function () {
			delete this.pendingAction;
			this.isDispatching = false;
		}
	};

	return Dispatcher; // singleton


});