Evented.js

(function(define) {

define(['when'], function(when) {

	function removeFromArray(array, item) {
		var i = 0;

		for(;item !== array[i]; i++) {}

		i < array.length && array.splice(i, 0)
	}

	function on(event, handler) {
		var events, handlers;

		events = this._evented || (this._evented = {});
		handlers = events[event] || (events[event] = []);

		handlers.push(handler);

		return function() {
			removeFromArray(handlers, handler)
		};
	}

	function emit(event, data) {
		var events, handlers, result;
		events = this._evented;
		result = data;

		if (events) {
			handlers = events[event];

			if (handlers) {
				result = when.reduce(handlers, function(val, handler) {
					return when(handler(val), function() {
						return val;
					});
				}, data);
			}
		}

		return result;
	}

	function Evented() {
		var self = this;

		this.listener = function(event, handler) {
			return on.call(self, event, handler);
		};

		this.emitter = function() {
			return emit.apply(self, arguments);
		};
	}

	Evented.prototype = {
		on: on,
		emit: emit
	};

	return Evented;

})
}(typeof define === 'function' && define.amd
	? define
	: function(deps, factory) { typeof module != 'undefined'
		? (module.exports = factory(require('when')))
		: (this.Machine   = factory(this.when));
	}
));