npm package: @stdlib/assert-is-leap-year
Description: Test if a value corresponds to a leap year in the Gregorian calendar.
Author: The Stdlib Authors
Latest version: 0.2.3

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# isLeapYear

[![NPM version][npm-image]][npm-url] [![Build Status][test-image]][test-url] [![Coverage Status][coverage-image]][coverage-url] <!-- [![dependencies][dependencies-image]][dependencies-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_.

<section class="installation">

## Installation

```bash
npm install @stdlib/assert-is-leap-year
```

</section>

<section class="usage">

## Usage

```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 <boolean>

bool = isLeapYear( new Date() );
// returns <boolean>

bool = isLeapYear( 2000 );
// returns true

bool = isLeapYear( 2017 );
// returns false
```

</section>

<!-- /.usage -->

<section class="notes">

## Notes

-   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
    ```

</section>

<!-- /.notes -->

<section class="examples">

## Examples

<!-- eslint no-undef: "error" -->

```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' );
}
```

</section>

<!-- /.examples -->



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<section class="related">

## See Also

-   <span class="package-name">[`@stdlib/assert-is-leap-year-cli`][@stdlib/assert-is-leap-year-cli]</span><span class="delimiter">: </span><span class="description">CLI package for use as a command-line utility.</span>


</section>

<!-- /.related -->

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<section class="main-repo" >

* * *

## Notice

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]

---

## License

See [LICENSE][stdlib-license].


## Copyright

Copyright &copy; 2016-2026. The Stdlib [Authors][stdlib-authors].

</section>

<!-- /.stdlib -->

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<section class="links">

[@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

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[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

</section>

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