Additional Properties Sheet - Send File via Form and AJAX

Hi all, I am trying to create an Additional Properties Sheet for our Custom Component, where users can upload a file to a URL. I realized this by adding a FORM element named "test_form" with a file Input. There is also a button calling the following JavaScript. While this works fine in a local web page executed in IE or Chrome, in DesignStudio the second alert is not triggered. So I bellieve there is something wrong with FormData. Can anyone help me how to find the error / debug this? Thanks! Thilo function uploadopenbi() { var l_object = document.getElementById("test_form");   alert(l_object); var l_fd = new FormData(l_object); alert(l_fd);   $.ajax({           type: "POST",           url: "http://localhost:9091/test.html",           data: l_fd, enctype: "multipart/form-data",               processData: false,                contentType: false,            success: function(data)           {               alert(data);           }         });