# Filename Extension
> [Regular expression][regexp] to capture a Windows filename extension.
## Usage
```javascript
var reExtnameWindows = require( '@stdlib/regexp/extname-windows' );
```
#### reExtnameWindows()
Returns a [regular expression][regexp] to capture a Windows filename extension.
```javascript
var RE_EXTNAME_WINDOWS = reExtnameWindows();
var ext = RE_EXTNAME_WINDOWS.exec( 'index.js' )[ 1 ];
// returns '.js'
```
#### reExtnameWindows.REGEXP
[Regular expression][regexp] to capture a Windows filename extension.
```javascript
var ext = reExtnameWindows.REGEXP.exec( 'C:\\foo\\bar\\index.js' )[ 1 ];
// returns '.js'
```
## Notes
- When executed against dotfile filenames (e.g., `.gitignore`), the [regular expression][regexp] does **not** capture the basename as a filename extension.
```javascript
var ext = reExtnameWindows.REGEXP.exec( '.bash_profile' )[ 1 ];
// returns ''
ext = reExtnameWindows.REGEXP.exec( '.travis.yml' )[ 1 ];
// returns '.yml'
```
## Examples
```javascript
var reExtnameWindows = require( '@stdlib/regexp/extname-windows' );
var RE_EXTNAME_WINDOWS = reExtnameWindows();
var ext;
ext = RE_EXTNAME_WINDOWS.exec( 'index.js' )[ 1 ];
// returns '.js'
ext = RE_EXTNAME_WINDOWS.exec( 'C:\\foo\\bar\\home.html' )[ 1 ];
// returns '.html'
ext = RE_EXTNAME_WINDOWS.exec( 'foo\\file.pdf' )[ 1 ];
// returns '.pdf'
ext = RE_EXTNAME_WINDOWS.exec( 'beep\\boop.' )[ 1 ];
// returns '.'
ext = RE_EXTNAME_WINDOWS.exec( '' )[ 1 ];
// returns ''
ext = RE_EXTNAME_WINDOWS.exec( '\\foo\\bar\\file' )[ 1 ];
// returns ''
ext = RE_EXTNAME_WINDOWS.exec( 'C:\\foo\\bar\\.gitignore' )[ 1 ];
// returns ''
```
[regexp]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions