js当年第一天和最后一天

function getFirstDayOfYear(year) {
  return new Date(year, 0, 1);
}

const firstDay = getFirstDayOfYear(2023);
console.log(firstDay); // 输出: 2023-01-01T00:00:00.000Z

function getLastDayOfYear(year) {
  const date = new Date(year, 11, 31);
  date.setDate(date.getDate() + 1);
  date.setDate(date.getDate() - 1);
  return date;
}

const lastDay = getLastDayOfYear(2023);
console.log(lastDay); // 输出: 2023-12-31T00:00:00.000Z

const firstDayUTC = firstDay.toISOString();
console.log(firstDayUTC); // 输出: "2023-01-01T00:00:00.000Z"

const lastDayUTC = lastDay.toISOString();
console.log(lastDayUTC); // 输出: "2023-12-31T00:00:00.000Z"