function request_demo()
{
// Disable button
document.form_demo.btn_demo.disabled=true;

  // Step 1. Create connection-object
  if (window.XMLHttpRequest)
    xmlHttp_request_demo=new XMLHttpRequest();// IE7+, Firefox, Chrome, Opera, Safari
  else        
    xmlHttp_request_demo=new ActiveXObject("Microsoft.XMLHTTP");// IE5, IE6    

  
  xmlHttp_request_demo.onreadystatechange=function()
  {
  if(xmlHttp_request_demo.readyState==4)
    {
      // Show sent-text
      document.form_demo.reset();
      document.form_demo.btn_demo.disabled=false;
      document.getElementById("txt_sent").style.display="block";
    }
  } 
  
  xmlHttp_request_demo.open("POST","includes/request_demo.php",true);
  var params = "&name="+document.form_demo.txt_name.value+"&tel="+document.form_demo.txt_tel.value+"&app="+document.form_demo.txt_app.value+"&lang="+document.form_demo.txt_lang.value;
  xmlHttp_request_demo.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
  xmlHttp_request_demo.setRequestHeader("Content-length", params.length);
  xmlHttp_request_demo.setRequestHeader("Connection", "close");
  xmlHttp_request_demo.send(params);    
}