preload example

private RequestStack $requestStack;

    public function __construct(RequestStack $requestStack)
    {
        $this->requestStack = $requestStack;
    }

    public function getFunctions(): array
    {
        return [
            new TwigFunction('link', $this->link(...)),
            new TwigFunction('preload', $this->preload(...)),
            new TwigFunction('dns_prefetch', $this->dnsPrefetch(...)),
            new TwigFunction('preconnect', $this->preconnect(...)),
            new TwigFunction('prefetch', $this->prefetch(...)),
            new TwigFunction('prerender', $this->prerender(...)),
        ];
    }

    /** * Adds a "Link" HTTP header. * * @param string $rel The relation type (e.g. "preload", "prefetch", "prerender" or "dns-prefetch") * @param array $attributes The attributes of this link (e.g. "['as' => true]", "['pr' => 0.5]") * * @return string The relation URI */

public function testLink()
    {
        $this->assertEquals('/foo.css', $this->extension->link('/foo.css', 'preload', ['as' => 'style', 'nopush' => true]));

        $link = (new Link('preload', '/foo.css'))->withAttribute('as', 'style')->withAttribute('nopush', true);
        $this->assertEquals([$link], array_values($this->request->attributes->get('_links')->getLinks()));
    }

    public function testPreload()
    {
        $this->assertEquals('/foo.css', $this->extension->preload('/foo.css', ['as' => 'style', 'crossorigin' => true]));

        $link = (new Link('preload', '/foo.css'))->withAttribute('as', 'style')->withAttribute('crossorigin', true);
        $this->assertEquals([$link], array_values($this->request->attributes->get('_links')->getLinks()));
    }

    public function testDnsPrefetch()
    {
        $this->assertEquals('/foo.css', $this->extension->dnsPrefetch('/foo.css', ['as' => 'style', 'crossorigin' => true]));

        $link = (new Link('dns-prefetch', '/foo.css'))->withAttribute('as', 'style')->withAttribute('crossorigin', true);
        $this->assertEquals([$link], array_values($this->request->attributes->get('_links')->getLinks()));
    }