I don't know how to get the value from the javascript function. Can anyone help?

private class CreateForAllLang : IAction
        {

            public string Alias
            {
                get { return "Create for All Languages"; }
            }

            public bool CanBePermissionAssigned
            {
                get { return true; }
            }

            public string Icon
            {
                get { return "images/about.png"; }
            }

            public string JsFunctionName
            {
                get { return "AddItem();"; }
            }

            public string JsSource
            {
                get
                {
                    return "function AddItem(){" +
                           "var multiLang = confirm('Create for all languages?');}";
                }
            }

            public char Letter
            {
                get { return 'ä'; }
            }

            public bool ShowInNotifier
            {
                get { return false; }
            }
        }