$(window).on("load", function() {

    /* load timer */
    window.setInterval(function() {
        var time = $("#timer").text();
        var t = time.split(":").map(t => parseInt(t));
        t[2] -= 1;
        if (t[2] < 0) {
            t[2] = 59;
            t[1] -= 1;
        }
        if (t[1] < 0) {
            t[1] = 59;
            t[0] -= 1;
        }
        if (t[0] < 0) {
            t[0] = 0;
            t[1] = 0;
            t[2] = 0;
        }
        $("#timer").text(t.join(":"));
    }, 1000);
});