IonicPopup.show() - shake on empty values instead of "nothing"

Question

I took sample code for the IonicPopup and I've modified the wifi password entry to be a username and password entry. It works as expected, but if you click the Login button without entering a username or password, all that happens is e.preventDefault().

Is there a way I can add an animation to the popup, perhaps a "shake" animation, if either field is left blank?

$scope.promptLogin = function() {

    $scope.data = {};

    // An elaborate, custom popup
    var myPopup = $ionicPopup.show({
        template: '<input type="text" placeholder="Username" ng-model="data.user"><br><input type="password" placeholder="Password" ng-model="data.pass">',
        title: 'Enter Credentials',
        subTitle: '',
        scope: $scope,
        buttons: [
        { text: 'Cancel' },
        {
            text: '<b>Login</b>',
            type: 'button-positive',
            onTap: function(e) {
            if (!$scope.data.user || !$scope.data.pass) {
                //don't allow the user to close unless he enters a user and pass
                e.preventDefault();
            } else {
                //console.log($scope.data.user + " - " + $scope.data.pass);
            }
            }
        }
        ]
    });

};