Test if a value corresponds to a leap year in the Gregorian calendar.
npm install @stdlib/assert-is-leap-yearWe believe in a future in which the web is a preferred environment for numerical computation. To help realize this future, we've built stdlib. stdlib is a standard library, with an emphasis on numerical and scientific computation, written in JavaScript (and C) for execution in browsers and in Node.js. The library is fully decomposable, being architected in such a way that you can swap out and mix and match APIs and functionality to cater to your exact preferences and use cases. When you use stdlib, you can be absolutely certain that you are using the most thorough, rigorous, well-written, studied, documented, tested, measured, and high-quality code out there. To join us in bringing numerical computing to the web, get started by checking us out on GitHub, and please consider financially supporting stdlib. We greatly appreciate your continued support!
About stdlib...
[![NPM version][npm-image]][npm-url] [![Build Status][test-image]][test-url] [![Coverage Status][coverage-image]][coverage-url]
> Test if a value corresponds to a [leap year][leap-year] in the [Gregorian calendar][gregorian-calendar].
A [leap year][leap-year] is defined as any year which is exactly divisible by 4, except for years which are exactly divisible by 100 and not by 400. In this definition, 100 corresponds to years marking a new century, and 400 corresponds to the length of the _leap cycle_.
``bash`
npm install @stdlib/assert-is-leap-year
`javascript`
var isLeapYear = require( '@stdlib/assert-is-leap-year' );
#### isLeapYear( \[value] )
Tests if a value corresponds to a [leap year][leap-year] in the [Gregorian calendar][gregorian-calendar].
`javascript
var bool = isLeapYear();
// returns
bool = isLeapYear( new Date() );
// returns
bool = isLeapYear( 2000 );
// returns true
bool = isLeapYear( 2017 );
// returns false
`
- If not provided any arguments, the function returns a boolean indicating if the current year (according to local time) is a [leap year][leap-year].
- If provided a value which is neither an integer value nor a [Date][date-object], the function always returns false.
`javascript
var bool = isLeapYear( '2016' );
// returns false
bool = isLeapYear( null );
// returns false
`
`javascript
var isLeapYear = require( '@stdlib/assert-is-leap-year' );
var bool;
var i;
for ( i = 0; i < 2021; i++ ) {
bool = isLeapYear( i );
console.log( 'The year %d %s a leap year.', i, ( bool ) ? 'is' : 'is not' );
}
`
- [@stdlib/assert-is-leap-year-cli][@stdlib/assert-is-leap-year-cli]: CLI package for use as a command-line utility.
*
This package is part of [stdlib][stdlib], a standard library for JavaScript and Node.js, with an emphasis on numerical and scientific computing. The library provides a collection of robust, high performance libraries for mathematics, statistics, streams, utilities, and more.
For more information on the project, filing bug reports and feature requests, and guidance on how to develop [stdlib][stdlib], see the main project [repository][stdlib].
#### Community
[![Chat][chat-image]][chat-url]
---
See [LICENSE][stdlib-license].
Copyright © 2016-2026. The Stdlib [Authors][stdlib-authors].
[@stdlib/assert-is-leap-year-cli]: https://www.npmjs.com/package/@stdlib/assert-is-leap-year-cli
[npm-image]: http://img.shields.io/npm/v/@stdlib/assert-is-leap-year.svg
[npm-url]: https://npmjs.org/package/@stdlib/assert-is-leap-year
[test-image]: https://github.com/stdlib-js/assert-is-leap-year/actions/workflows/test.yml/badge.svg?branch=v0.2.3
[test-url]: https://github.com/stdlib-js/assert-is-leap-year/actions/workflows/test.yml?query=branch:v0.2.3
[coverage-image]: https://img.shields.io/codecov/c/github/stdlib-js/assert-is-leap-year/main.svg
[coverage-url]: https://codecov.io/github/stdlib-js/assert-is-leap-year?branch=main
[chat-image]: https://img.shields.io/badge/zulip-join_chat-brightgreen.svg
[chat-url]: https://stdlib.zulipchat.com
[stdlib]: https://github.com/stdlib-js/stdlib
[stdlib-authors]: https://github.com/stdlib-js/stdlib/graphs/contributors
[cli-section]: https://github.com/stdlib-js/assert-is-leap-year#cli
[cli-url]: https://github.com/stdlib-js/assert-is-leap-year/tree/cli
[@stdlib/assert-is-leap-year]: https://github.com/stdlib-js/assert-is-leap-year/tree/main
[umd]: https://github.com/umdjs/umd
[es-module]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Modules
[deno-url]: https://github.com/stdlib-js/assert-is-leap-year/tree/deno
[deno-readme]: https://github.com/stdlib-js/assert-is-leap-year/blob/deno/README.md
[umd-url]: https://github.com/stdlib-js/assert-is-leap-year/tree/umd
[umd-readme]: https://github.com/stdlib-js/assert-is-leap-year/blob/umd/README.md
[esm-url]: https://github.com/stdlib-js/assert-is-leap-year/tree/esm
[esm-readme]: https://github.com/stdlib-js/assert-is-leap-year/blob/esm/README.md
[branches-url]: https://github.com/stdlib-js/assert-is-leap-year/blob/main/branches.md
[stdlib-license]: https://raw.githubusercontent.com/stdlib-js/assert-is-leap-year/main/LICENSE
[leap-year]: https://en.wikipedia.org/wiki/Leap_year
[gregorian-calendar]: https://en.wikipedia.org/wiki/Gregorian_calendar
[date-object]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date
[standard-streams]: https://en.wikipedia.org/wiki/Standard_streams
[mdn-regexp]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions