state.js

angular.module('services', [])
  .factory('State', function ($rootScope) {
    'use strict';
    var state;

    var broadcast = function (state) {
      $rootScope.$broadcast('State.Update', state);
    };

    var update = function (newState) {
      state = newState;
      broadcast(state);
    };
    
    var onUpdate = function ($scope, callback) {
      $scope.$on('State.Update', function (newState) {
        callback(newState);
      });
    };

    return {
      update: update,
      state: state,
      listen: listen
    };
  });