function ajax()
{
    var xhr=null;
  	 
    if (window.XMLHttpRequest) { 
        xhr = new XMLHttpRequest();
    }
    else if (window.ActiveXObject) 
    {
        xhr = new ActiveXObject("Microsoft.XMLHTTP");
    }
    //on appelle le fichier reponse.txt
    xhr.open("POST", "reponse.php", true);
	xhr.setRequestHeader('Content-Type','application/x-www-form-urlencoded');
	nom1=document.getElementById('nom').value;
	
	xhr.send("nom1="+nom1);
    
       alert(xhr.responseText);
}