A helper function for Laravel that can add missing target blank to HTML so that external links open in a new tab

add_target_blank_to_external_links.php

<?php

if (!function_exists('is_external_url')) {
    /**
     * Check if a URL is external
     */
    function is_external_url(string $url)
    {
        $test = str(config('app.url'))->basename()->prepend('*')->append('*')->toString();

        return str($url)->is($test, true) === false;
    }
}

if (!function_exists('add_target_blank_to_external_links')) {
    /**
     * Takes in an HTML string and makes sure that any external URLs are marked as target blank
     */
    function add_target_blank_to_external_links(string|\Illuminate\Support\Stringable $escapedHtml)
    {
        $html = stripslashes($escapedHtml);

        $doc = new \DOMDocument();
        $doc->loadHTML($html, LIBXML_HTML_NOIMPLIED | LIBXML_HTML_NODEFDTD);

        $xpath = new \DOMXPath($doc);

        /** @var \DOMElement */
        $links = $xpath->query('//a[@href]');

        foreach ($links as $link) {
            $href = $link->attributes->getNamedItem('href')->value;
            if (\Illuminate\Support\Facades\URL::isValidUrl($href) && is_external_url($href)) {
                $link->setAttribute('target', '_blank');
                $link->setAttribute('rel', 'noopener');
            }
        }

        return str($doc->saveHTML())->toHtmlString();
    }
}