Syncing state of complex models with local/session storage about ngstorage HOT 2 CLOSED

angular
    .module('Survey',['ngStorage'])
    .factory('Answer',($sessionStorage,$stateParams) ->
        _blankAnswer = {
            title: null
            value: null
        }
        class Answer
            constructor: ->
                self = @
                survey_id = $stateParams.survey_id
                question_id = $stateParams.question_id
                angular.extend(this, $sessionStorage.surveys[survey_id].questions[question_id].answer || _blankAnswer)
                $rootScope.$watch(
                    ->
                        self
                    ,(newValue, oldValue) ->
                        $sessionStorage.surveys[survey_id].questions[question_id] = newValue
                    ,true
                )
            # methods & custom attrs here
    )
    .controller('answerCtrl',(Answer) ->
        $scope.answer = new Answer()
    )

$sessionStorage.surveys[survey_id].questions[question_id].answer = this