function diff(start, end) {
    start = document.getElementById("start").value; //to update time value in each input bar
    end = document.getElementById("end").value; //to update time value in each input bar
    
    start = start.split(":");
    end = end.split(":");
    var startDate = new Date(0, 0, 0, start[0], start[1], 0);
    var endDate = new Date(0, 0, 0, end[0], end[1], 0);
    var diff = endDate.getTime() - startDate.getTime();
    var hours = Math.floor(diff / 1000 / 60 / 60);
    diff -= hours * 1000 * 60 * 60;
    var minutes = Math.floor(diff / 1000 / 60);

    return (hours < 9 ? "0" : "") + hours + ":" + (minutes < 9 ? "0" : "") + minutes;
}