Ajax works only through false how to be?

Question

JavaScript

ajax works only synchronously and asynchronously does not work what am I doing wrong?
var req = new XMLHttpRequest();

req.open('POST','FlieTest17.php',true);
req.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
req send(body);

Answer 1

var req = new XMLHttpRequest();
req.open('POST','FlieTest17.php',true);
req.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded'); 
req.onreadystatechange = function (aEvt) {
  if (req.readyState == 4) {
     if(req.status == 200)
      {
           // тут обрабатываем ответ
      }
     else
      dump("Error loading page\n");
  }
};