emitter.js

'use strict';

function unsubscribe(subscribers, callback){
	return function(){
		var index = subscribers.indexOf(callback);

		if(index > -1){
			subscribers.splice(index, 1);
		}
	};
}

function noop(){}

module.exports = function(){
	var subscribers = [];

	return {
		subscribe: function(callback){
			if(subscribers.indexOf(callback) < 0){
				subscribers.unshift(callback);

				return unsubscribe(subscribers, callback);
			}

			return noop;
		},
		publish: function(data){
			var index = subscribers.length;

			while(--index >= 0){
				subscribers[index](data);
			}
		}
	};
};

example.js

app.service('Users', function(){
	return new Store({
		getInitialState: function(){
			return [];
		},
		add: function(users, name){
			return users.concat({ name: name });
		}
	});
});

app.controller('UsersCtrl', function($scope, Users){
	Users.linkTo($scope, 'users');
	
	$scope.addUser = Users.action('add');
});

store.js

var emitter = require('./emitter');

function assign(target, source){
	Object.keys(source).forEach(function(key){
		target[key] = source[key];
	});
}

function apply(scope, key, state){
	scope.$apply(function(){
		scope[key] = state;
	});
}

function Store(reducers){
	this.reducers = reducers;
	this.state = null;
	this.emitter = emitter();
}

Store.prototype.linkTo = function(scope, key){
	this.emitter.subscribe(function(state){
		apply(scope, key, state);
	});
	
	if(!this.state){
		this.state = this.reducers.getInitialState();
	}
	
	apply(scope, key, this.state);
};

Store.prototype.action = function action(key, data){
	if(arguments.length < 2){
		return action.bind(this, key);
	}
	
	assign(this.state, this.reducers[key](this.state, data))
	this.emitter.publish(this.state);
};