//Initialize XMLHttpRequest
function getXhr(){
   var xhr = null;
   if(window.XMLHttpRequest){ //Firefox and others
      xhr = new XMLHttpRequest(); 
   }
   else if(window.ActiveXObject){ //Internet Explorer 
      try {
        xhr = new ActiveXObject("Msxml2.XMLHTTP");
      } catch (e) {
        xhr = new ActiveXObject("Microsoft.XMLHTTP");
      }
   }
   else { // XMLHttpRequest not supported by browser
      alert("Votre navigateur ne supporte pas les objets XMLHTTPRequest..."); 
      xhr = false; 
   } 
   return xhr;
}