function ajax(page)
{
  var xhr=null;
  if(window.XMLHttpRequest) // Firefox et autres
  {
    xhr = new XMLHttpRequest();
  }  
  else
  { 
    if(window.ActiveXObject)
    { // Internet Explorer
      try 
      {
        xhr = new ActiveXObject("Msxml2.XMLHTTP");
      } catch (e) {
        try {
          xhr = new ActiveXObject("Microsoft.XMLHTTP");
        } catch (e1) {
          xhr = null;
        }
      }
    }
  }
  
  if (xhr == null) { // XMLHttpRequest non supporté par le navigateur
    alert("Votre navigateur ne supporte pas les objets XMLHTTPRequest...");
  }
  else
  {
  xhr.onreadystatechange = function() { alert_ajax(xhr); };
  document.getElementById("mainframe").style.visibility = "hidden";
  document.getElementById("message").className="loadvisible";
  xhr.open("POST", page, true);
  xhr.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
  xhr.send(null);
  }
}

function alert_ajax(xhr)
{
    if (xhr.readyState==4) 
    {
    	var docHTML= xhr.responseText;
    	document.getElementById("mainframe").innerHTML=docHTML;
    	document.getElementById("message").className="loadhidden";
    	document.getElementById("mainframe").style.visibility = "visible";
    }
}

function change_class(eltid,classname)
{
    var elt = document.getElementById(eltid); 
    elt.className= classname; 

}