js 上个月

function getLastMonth() {
  const now = new Date();
  const year = now.getFullYear();
  const month = now.getMonth();

  let lastMonthYear = year;
  let lastMonth = month - 1;

  if (lastMonth < 0) {
    lastMonthYear -= 1;
    lastMonth = 11;
  }

  return { year: lastMonthYear, month: lastMonth + 1 }; // 返回的月份加1，使其符合常规表示
}

console.log(getLastMonth()); // 输出类似 { year: 2023, month: 4 } 表示上个月是2023年4月

function getLastDayOfLastMonth() {
  const now = new Date();
  const year = now.getFullYear();
  const month = now.getMonth();

  let lastMonthYear = year;
  let lastMonth = month - 1;

  if (lastMonth < 0) {
    lastMonthYear -= 1;
    lastMonth = 11;
  }

  const lastDayOfMonth = new Date(lastMonthYear, lastMonth + 1, 0);
  return lastDayOfMonth;

}

console.log(getLastDayOfLastMonth()); // 输出类似 2023-04-30T23:59:59.999Z 表示上个月的最后一天

function formatDate(date) {
  const year = date.getFullYear();
  const month = String(date.getMonth() + 1).padStart(2, '0');
  const day = String(date.getDate()).padStart(2, '0');
  return `${year}-${month}-${day}`;
}

const lastDayOfLastMonth = getLastDayOfLastMonth();
console.log(formatDate(lastDayOfLastMonth)); // 输出类似 2023-04-30