Сколько секунд прошло с начала сегодняшнего дня и количество секунд до завтрашней даты

function secondsSinceStartOfToday() {
    const now = new Date();
    const startOfToday = new Date(
        now.getFullYear(),
        now.getMonth(),
        now.getDate()
    );
    return Math.floor((now - startOfToday) / 1000);
}
function secondsUntilTomorrow() {
    const now = new Date();
    const startOfTomorrow = new Date(
        now.getFullYear(),
        now.getMonth(),
        now.getDate() + 1
    );
    return Math.floor((startOfTomorrow - now) / 1000);
}

function getSecondsToday() {
  let now = new Date();
  let today = new Date(now.getFullYear(), now.getMonth(), now.getDate());
  let diff = now - today;
  return Math.round(diff / 1000);
}
 
alert( getSecondsToday() );

function getSecondsToTomorrow() {
  let now = new Date();
  let tomorrow = new Date(now.getFullYear(), now.getMonth(), now.getDate()+1);
  let diff = tomorrow - now;
  return Math.round(diff / 1000);
}

function getSecondsToday() {
  let d = new Date();
  return d.getHours() * 3600 + d.getMinutes() * 60 + d.getSeconds();
}

function getSecondsToTomorrow() {
  let now = new Date();
  let hour = now.getHours();
  let minutes = now.getMinutes();
  let seconds = now.getSeconds();
  let totalSecondsToday = (hour * 60 + minutes) * 60 + seconds;
  let totalSecondsInADay = 86400;
 
  return totalSecondsInADay - totalSecondsToday;
}