How to store a JSON Variable with AngularJS ngStorage to $sessionStorage

I have the following variable which is easily transformed to a JSON-String:

var data = {
    ball: {
        colour: "",
        size: "",
        price: ""
    },
    toys: []
}

In my Controller I want add this variable to the scope like:

$scope.data = angular.copy(data)

Then I want it to store on the $sessionStorage like:

$sessionStorage.data = angular.toJson($scope.data);

After the page refresh the $scope.data is empty again. Any ideas?

This is how my code works:

    $scope.$storage = $sessionStorage;

    if (typeof $scope.$storage.data !== 'undefined') {
        $scope.data = $scope.$storage.data;
    } else {
        $scope.data = angular.copy(data);
        $scope.$storage.data = $scope.data;
    }

A shorter solution would be:

    $scope.cv = $scope.$storage.cv || angular.copy(cv);
    $scope.$storage.cv = $scope.cv;