中文
devexamples

Leap Year Check and Days in a Month

Apply Gregorian leap-year rules and return the exact number of days in any month, including February in leap and common years.

JavascriptData Integrity

Code

snippet
export function isLeapYear(year) {
  if (!Number.isInteger(year) || year < 1 || year > 9999) {
    throw new RangeError("year must be an integer between 1 and 9999");
  }
  return year % 4 === 0 && (year % 100 !== 0 || year % 400 === 0);
}

export function daysInMonth(year, month) {
  if (!Number.isInteger(month) || month < 1 || month > 12) {
    throw new RangeError("month must be an integer between 1 and 12");
  }
  const lengths = [
    31,
    isLeapYear(year) ? 29 : 28,
    31, 30, 31, 30, 31, 31, 30, 31, 30, 31,
  ];
  return lengths[month - 1];
}

Related Examples