function showMessagePane(bool, idMessage) {

    var msg = document.getElementById(idMessage);

    if (!msg)

        alert('ERREUR showMessagePane: l\'élément "Message" n\'existe pas!');

    else {

        if (bool) {

            msg.style.display = "block";

            // Fermeture automatique

            var x = 1;  // initial step for opacity

            function opacity(x) {

                var y =

                    - 9 * Math.pow(10, -9) * Math.pow(x, 6)

                    + 1 * Math.pow(10, -6) * Math.pow(x, 5)

                    - 8 * Math.pow(10, -5) * Math.pow(x, 4)

                    + 0.0027 * Math.pow(x, 3)

                    - 0.0448* Math.pow(x, 2)

                    + 0.3817 * x

                    - 0.2718;

                if ( y > 1) return 1;

                else if (y < 0) return 0;

                else return y;

            }

            var timer = setInterval(function () {

                var opa = opacity(x);

                if (opa <= 0.01){

                    msg.style.display = 'none';

                    clearInterval(timer);

                }

                msg.style.opacity = opa;

                msg.style.filter = 'alpha(opacity=' + opa * 100 + ")";

                x += 1;

            }, 100);

        } else {

            msg.style.display = "none";

        }

    }

}

​

showMessagePane(true, 'Message');