An observable decorator

observer.js

/**
 * Creates or decorates an object with observable behavior.
 * @param  {[type]} o object to decorate
 * @return {[type]}   the observable object
 */
function makeObservable (o) {
	var undef;

	o = o || {};

	if (o.subscribers) {
		throw('Object is already an Observable');
	}
	o.subscribers = { any: [] };

	o.subscribe = function (fn, type) {
		type = type || 'any';
		if (o.subscribers[type] === undef) {
			o.subscribers[type] = [];
		}
		o.subscribers[type].push(fn);
	};

	o.unsubscribe = function (fn, type) {
		var subscribers = o.subscribers[type || 'any'],
			i = subscribers.length;

		while (i--) {
			if (subscribers[i] === fn) {
				subscribers.splice(i, 1);
			}
		}
	};

	o.publish = function (message, type) {
		var subscribers = o.subscribers[type || 'any'],
			i = subscribers.length;

		while (i--) {
			if (subscribers[i] === fn) {
				subscribers[i](message);
			}
		}
	};

	return o;
};