function a_schr(s_in)
{
  var xhr = createXHR();
  xhr.onreadystatechange = function()
  {
    if (xhr.readyState == 4)
    {
      if (xhr.status == 200){
        // vypiseme vracena data ze scriptu
        alert(xhr.responseText);
        
        //document.getElementById('schr_pocet').value = xhr.responseText;
        //document.getElementById("xxx").innerHTML = xhr.responseText; //zmeni vse v divu

      }else{
        // pozadavek se nepodarilo zpracovat
        alert('Pozadavek se nepodarilo zpracovat. Zkuste to za chvili znovu.');
      }
    }
  };

  // parametry, ktere predame
  var parameters = "box=" + encodeURIComponent(s_in);
  // volany soubor
  xhr.open("POST", "/schranka_ajax.php", true);
  xhr.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
  xhr.send(parameters);
}

/**
 * Vytvoreni AJAX objektu
 * @return ajax objekt
 */
function createXHR()
{
  var request = false;
  try {
    request = new ActiveXObject('Msxml2.XMLHTTP');
  }
  catch (err2) {
    try {
        request = new ActiveXObject('Microsoft.XMLHTTP');
    }
    catch (err3) {
      try {
        request = new XMLHttpRequest();
      }
      catch (err1)
      {
        request = false;
      }
    }
  }
  return request;
}