Data.prototype.send = function() {
  'use strict';
  var formData = new FormData();
  formData.append('file', this.file, this.name);
  if (this.property !== undefined) {
    formData.append('property', this.property);
  }
  var request = new XMLHttpRequest();

  request.upload.addEventListener('progress', function(e) {
    var pc = parseInt(100 - (e.loaded / e.total * 100));
    //Co tutaj?
  }, false);

  request.onreadystatechange = function(e) {
    if (xhr.readyState == 4) {
      //Co tutaj?
    }
  };
  request.open('POST', upload.php, true);
  request.send(formData);
};