Skip to main content
Using Deno in production at your company? Earn free Deno merch.
Give us feedback
Module

std/datetime/is_leap.ts

Deno standard library
Go to Latest
File
// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.// This module is browser compatible.
/** * Returns whether the given date or year (in number) is a leap year or not in the local time zone. * based on: https://docs.microsoft.com/en-us/office/troubleshoot/excel/determine-a-leap-year * * @example * ```ts * import { isLeap } from "https://deno.land/std@$STD_VERSION/datetime/is_leap.ts"; * * isLeap(new Date("1970-01-02")); // => returns false * isLeap(new Date("1972-01-02")); // => returns true * isLeap(new Date("2000-01-02")); // => returns true * isLeap(new Date("2100-01-02")); // => returns false * isLeap(1972); // => returns true * ``` * * Some dates may return different values depending on your timezone. * * @example * ```ts * import { isLeap } from "https://deno.land/std@$STD_VERSION/datetime/is_leap.ts"; * * isLeap(new Date("2000-01-01")); // => returns true if the local timezone is GMT+0, returns false if the local timezone is GMT-1 * isLeap(2000); // => returns true regardless of the local timezone * ``` * * @param year year in number or Date format */export function isLeap(year: Date | number): boolean { const yearNumber = year instanceof Date ? year.getFullYear() : year; return isYearNumberALeapYear(yearNumber);}
/** * Returns whether the given date or year (in number) is a leap year or not in UTC time. This always returns the same value regardless of the local timezone. * based on: https://docs.microsoft.com/en-us/office/troubleshoot/excel/determine-a-leap-year * * @example * ```ts * import { isUtcLeap } from "https://deno.land/std@$STD_VERSION/datetime/is_leap.ts"; * * isUtcLeap(2000); // => returns true regardless of the local timezone * isUtcLeap(new Date("2000-01-01")); // => returns true regardless of the local timezone * isUtcLeap(new Date("January 1, 2000 00:00:00 GMT+00:00")); // => returns true regardless of the local timezone * isUtcLeap(new Date("December 31, 2000 23:59:59 GMT+00:00")); // => returns true regardless of the local timezone * isUtcLeap(new Date("January 1, 2000 00:00:00 GMT+01:00")); // => returns false regardless of the local timezone * isUtcLeap(new Date("December 31, 2000 23:59:59 GMT-01:00")); // => returns false regardless of the local timezone * isUtcLeap(new Date("January 1, 2001 00:00:00 GMT+01:00")); // => returns true regardless of the local timezone * isUtcLeap(new Date("December 31, 1999 23:59:59 GMT-01:00")); // => returns true regardless of the local timezone * ``` * * @param year year in number or Date format */export function isUtcLeap(year: Date | number): boolean { const yearNumber = year instanceof Date ? year.getUTCFullYear() : year; return isYearNumberALeapYear(yearNumber);}
function isYearNumberALeapYear(yearNumber: number): boolean { return ( (yearNumber % 4 === 0 && yearNumber % 100 !== 0) || yearNumber % 400 === 0 );}