# isLeapYear
> 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_.
## 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
bool = isLeapYear( new Date() );
// returns
bool = isLeapYear( 2000 );
// returns true
bool = isLeapYear( 2017 );
// returns false
```
## 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
```
## Examples
```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' );
}
```
* * *
## CLI
### Usage
```text
Usage: is-leap-year [options] []
Options:
-h, --help Print this message.
-V, --version Print the package version.
```
### Examples
```bash
$ is-leap-year
$ is-leap-year 1993
false
```
To use as a [standard stream][standard-streams],
```bash
$ echo -n 1992 | is-leap-year
true
```
[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