Speculation Rules API (WordPress Plugin)

speculation-rules-prefetch.php

<?php
/**
 * Plugin Name: Speculation Rules Prefetch
 * Description: A WordPress plugin to prefetch links using Speculation Rules API
 * Version: 1.0
 * Author: Max Ziebell
 */
 
 // Hook for adding speculation rules to the WordPress footer
 add_action('wp_footer', 'add_speculation_rules');

// Action function for the above hook
function add_speculation_rules() {
	?>
	<script>
		// Feature detect Speculation Rules API support
		if (HTMLScriptElement.supports && HTMLScriptElement.supports('speculationrules')) {
			// Get all anchor tags in the document
			const anchors = Array.from(document.querySelectorAll('a'));
			
			// Filter out external links
			const sameDomainLinks = anchors
				.map(a => a.href)
				.filter(href => new URL(href).origin === window.location.origin);

			// Create speculation rules script element
			const specScript = document.createElement('script');
			specScript.type = 'speculationrules';

			const specRules = {
				prefetch: [
					{
						source: 'list',
						urls: sameDomainLinks,
					},
				],
			};

			specScript.textContent = JSON.stringify(specRules);
			console.log('Added speculation rules for prefetching');
			document.body.appendChild(specScript);
		} else {
			console.log('Your browser does not support the Speculation Rules API.');
		}
	</script>
	<?php
}