[Аркадий Укупник]

function post(url, cb, data) {
  var req = new XMLHttpRequest;
  req.open('POST', url);
  // req.setRequestHeader('X-Requested-With', 'XMLHttpRequest');
  req.onload = function () {
    try {
      req.responseJSON = JSON.parse(req.responseText);
    } catch (e) {}
    cb.call(this, req);
  };
  if (isFormElement(data)) { // data instanceof HTMLFormElement
    data = new FormData(data);
  } else if (false == data instanceof FormData) {
    req.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
    if (isPlainObject(data)) { // typeof data=='object'
      data = buildQuery(data); // var temp=[];for(var i in data) temp.push(encodeURIComponent(i)+'='+encodeURIComponent(data[i]));data=temp.join('&');
    }
  }
  req.send(data);
}