function xmlhttpPost(strURL) {
    var xmlHttpReq = false;
    var self = this;
    // Mozilla/Safari
    if (window.XMLHttpRequest) {
        self.xmlHttpReq = new XMLHttpRequest();
    }
    // IE
    else if (window.ActiveXObject) {
        self.xmlHttpReq = new ActiveXObject("Microsoft.XMLHTTP");
    }
    self.xmlHttpReq.open('POST', strURL, true);
    self.xmlHttpReq.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
    self.xmlHttpReq.onreadystatechange = function() {
        if (self.xmlHttpReq.readyState == 4) {
            updatepage(self.xmlHttpReq.responseText);
            if (self.xmlHttpReq.responseText == "Demande envoyée.") {
              DisableButtonContact();
            }
        }
    }
    self.xmlHttpReq.send(getquerystring());
}

function DisableButtonContact() {
  var form = document.forms['mailerform'];
  form.Valider.disabled=true;
}

function getquerystring() {
    var form = document.forms['mailerform'];
    var nom = form.nom.value;
    var mailcli = form.mailcli.value;
    var objmsg = form.objmsg.value;
    var msg = form.msg.value;
    qstr = 'mailcli=' + encodeURIComponent(mailcli) + '&msg=' + escape(msg) + '&objmsg=' + escape(objmsg) + '&nom=' + escape(nom);
    // Remarque: pas de '?' avant la chaine de requete
    return qstr;
}

function updatepage(str){
    document.getElementById("contact_msg").innerHTML = str;
}