code: function upload(file_mngr_url, file, filename, success, error) {
      // Assemble data
      var fd = new FormData();
      fd.append("filename", filename);
      fd.append("file", file);
      var req = new XMLHttpRequest();
      req.open("POST", file_mngr_url + "/upload");
      req.onload = function(e) {
          var url = JSON.parse(req.response).url;
          if (url === undefined)
              error();
          else
              success(url);
      };
      req.send(fd);
  }
docs: Helper function This function uploads a file with a certain file name. If the upload is successful the first callback is executed, otherwise the second one is.