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---
layout: default
title: External Links Extension
description: The ExternalLinksExtension detects external links and adjusts their HTML markup
---
# External Links Extension
This extension can detect links to external sites and adjust the markup accordingly:
- Make the links open in new tabs/windows
- Adds a `rel` attribute to the resulting `<a>` tag with values like `"nofollow noopener noreferrer"`
- Optionally adds any custom HTML classes
## Installation
This extension is bundled with `league/commonmark`. This library can be installed via Composer:
```bash
composer require league/commonmark
```
See the [installation](/2.1/installation/) section for more details.
## Usage
Configure your `Environment` as usual and simply add the `ExternalLinkExtension` provided by this package:
```php
use League\CommonMark\Environment\Environment;
use League\CommonMark\Extension\CommonMark\CommonMarkCoreExtension;
use League\CommonMark\Extension\ExternalLink\ExternalLinkExtension;
use League\CommonMark\MarkdownConverter;
// Define your configuration, if needed
$config = [
'external_link' => [
'internal_hosts' => 'www.example.com', // TODO: Don't forget to set this!
'open_in_new_window' => true,
'html_class' => 'external-link',
'nofollow' => '',
'noopener' => 'external',
'noreferrer' => 'external',
],
];
// Configure the Environment with all the CommonMark parsers/renderers
$environment = new Environment($config);
$environment->addExtension(new CommonMarkCoreExtension());
// Add this extension
$environment->addExtension(new ExternalLinkExtension());
// Instantiate the converter engine and start converting some Markdown!
$converter = new MarkdownConverter($environment);
echo $converter->convertToHtml('I successfully installed the <https://github.com/thephpleague/commonmark> project!');
```
## Configuration
This extension supports three configuration options under the `external_link` configuration:
### `internal_hosts`
This option defines a list of hosts which are considered non-external and should not receive the external link treatment.
This can be a single host name, like `'example.com'`, which must match **exactly**.
Wildcard matching is also supported using regular expression like `'/(^|\.)example\.com$/'`. Note that you must use `/` characters to delimit your regex.
This configuration option also accepts an array of multiple strings and/or regexes:
```php
$config = [
'external_link' => [
'internal_hosts' => ['foo.example.com', 'bar.example.com', '/(^|\.)google\.com$/],
],
];
```
By default, if this option is not provided, all links will be considered external.
### `open_in_new_window`
This option (which defaults to `false`) determines whether any external links should open in a new tab/window.
### `html_class`
This option allows you to provide a `string` containing one or more HTML classes that should be added to the external link `<a>` tags: No classes are added by default.
### `nofollow`, `noopener`, and `noreferrer`
These options allow you to configure whether a `rel` attribute should be applied to links. Each of these options can be set to one of the following `string` values:
- `'external'` - Apply to external links only
- `'internal'` - Apply to internal links only
- `'all'` - Apply to all links (both internal and external)
- `''` (empty string) - Don't apply to any links
Unless you override these options, `nofollow` defaults to `''` and the others default to `'external'`.
## Advanced Rendering
When an external link is detected, the `ExternalLinkProcessor` will set the `external` data option on the `Link` node to either `true` or `false`. You can therefore create a [custom link renderer](/2.1/customization/rendering/) which checks this value and behaves accordingly:
```php
use League\CommonMark\Extension\CommonMark\Node\Inline\Link;
use League\CommonMark\Renderer\ChildNodeRendererInterface;
use League\CommonMark\Renderer\NodeRendererInterface;
use League\CommonMark\Util\HtmlElement;
class MyCustomLinkRenderer implements NodeRendererInterface
{
/**
* @param Node $node
* @param ChildNodeRendererInterface $childRenderer
*
* @return HtmlElement
*/
public function render(Node $node, ChildNodeRendererInterface $childRenderer)
{
if (!($node instanceof Link)) {
throw new \InvalidArgumentException('Incompatible node type: ' . \get_class($node));
}
if ($node->data->get('external')) {
// This is an external link - render it accordingly
} else {
// This is an internal link
}
// ...
}
}
```
## Adding Icons
You can also use CSS to automagically add an external link icon by targeting the `html_class` given in the configuration:
```css
// Font Awesome example:
a[target="_blank"]::after,
a.external::after {
content: "\f08e";
font: normal normal normal 14px/1 FontAwesome;
}
// Glyphicon example:
a[target="_blank"]::after,
a.external::after {
@extend .glyphicon;
content: "\e164";
margin-left: .5em;
margin-right: .25em;
}
```
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