var xhr;
function sendRequest()      {
  if (window.XMLHttpRequest)  {
    xhr = new XMLHttpRequest()  ;
    xhr.onreadystatechange = handleResponse ;
    xhr.open("GET", "lab5_F01.php", true);
    xhr.send(null); 
  } else {
    return (null) ;
  }
}

function handleResponse()      {
  if (xhr.readyState == 4)    {
    alert(xhr.responseText) ;
  }
}