Example of FormaData for Chrome and Firefox

gistfile1.js

    $.each(dataTransfer.files, function ( i, file ) {
      var xhr    = new XMLHttpRequest();
      var upload = xhr.upload;
      var formdata = new FormData();

      //formdata.append("session",socket.transport.sessionid);
      formdata.append('mycustomfieldforfile', file);
      xhr.open("POST", "/post/file");
      xhr.send(formdata);

    });