var xhr = new XMLHttpRequest();
      xhr.open(method, url, true);
      //xhr.setRequestHeader("Content-type", "application/x-www-form-urlencoded");

      xhr.onreadystatechange = function() {
        if (xhr.readyState === 4 && xhr.status === 200) {
          var type = xhr.getResponseHeader('Content-Type');

          if (type.match(/^text/))
            callback(xhr.responseText);
        }
      };

      xhr.send();