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<?php |
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/** |
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* Metasync_Smart_Lazy_Loader |
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* Adds loading="lazy" to images and iframes while protecting LCP elements. |
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* |
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* @package Search Atlas SEO |
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* @copyright Copyright (C) 2021-2025, Search Atlas Group - [email protected] |
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* @since 2.6.0 |
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*/ |
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|
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if (!defined('ABSPATH')) { |
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exit; |
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} |
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|
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class Metasync_Smart_Lazy_Loader { |
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|
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private array $settings; |
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|
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public function __construct(array $settings) { |
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$this->settings = $settings; |
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|
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// Tell WordPress to skip lazy loading for the first N images (WP 5.9+) |
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$skip = (int) ($settings['lcp_skip_count'] ?? 2); |
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add_filter('wp_omit_loading_attr_threshold', fn() => $skip); |
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|
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// For broader control (including non-WP images and iframes), filter content |
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add_filter('the_content', [$this, 'process_content'], 25); |
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add_filter('post_thumbnail_html', [$this, 'process_content'], 25); |
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add_filter('widget_text', [$this, 'process_content'], 25); |
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} |
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|
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/** |
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* Process HTML content to add/manage lazy loading attributes. |
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*/ |
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public function process_content(string $content): string { |
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if (empty($content) || is_admin() || is_feed() || $this->is_amp_request()) { |
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return $content; |
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} |
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|
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$content = $this->process_images($content); |
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|
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if (!empty($this->settings['lazy_load_iframes'])) { |
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$content = $this->process_iframes($content); |
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} |
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|
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return $content; |
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} |
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|
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/** |
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* Add loading="lazy" to <img> tags, skipping the first N for LCP. |
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*/ |
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private function process_images(string $content): string { |
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$skip = (int) ($this->settings['lcp_skip_count'] ?? 2); |
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$exclude_classes = array_filter(array_map('trim', explode(',', $this->settings['exclude_classes'] ?? ''))); |
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|
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// The LCP budget is scoped to a single content block (the same |
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// semantics as core's wp_omit_loading_attr_threshold): an |
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// instance-wide counter shared across the_content, thumbnails, and |
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// widgets counted tags in filter-execution order, not document |
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// order, so the hero could still end up lazy-loaded. |
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$position = 0; |
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|
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return preg_replace_callback('/<img\s[^>]+>/i', function ($matches) use ($skip, $exclude_classes, &$position) { |
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$tag = $matches[0]; |
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|
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// Already has a loading attribute - don't touch it |
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if (preg_match('/\sloading\s*=/i', $tag)) { |
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return $tag; |
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} |
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|
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// Check excluded classes |
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if (!empty($exclude_classes) && preg_match('/class=["\']([^"\']+)["\']/i', $tag, $class_match)) { |
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$classes = explode(' ', $class_match[1]); |
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foreach ($exclude_classes as $excluded) { |
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if (in_array($excluded, $classes, true)) { |
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return $tag; |
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} |
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} |
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} |
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|
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// Only images this filter actually modifies consume the budget; |
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// already-lazy and excluded tags above must not. |
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$position++; |
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|
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// Skip first N images to protect LCP |
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if ($position <= $skip) { |
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return $this->inject_attribute($tag, 'loading', 'eager'); |
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} |
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|
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// Add loading="lazy" and decoding="async" for below-fold images |
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$tag = $this->inject_attribute($tag, 'loading', 'lazy'); |
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$tag = $this->inject_attribute($tag, 'decoding', 'async'); |
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|
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return $tag; |
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}, $content); |
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} |
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|
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/** |
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* Add loading="lazy" to <iframe> tags. |
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*/ |
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private function process_iframes(string $content): string { |
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// Same skip semantics as images: the first N iframes (typically |
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// above-fold embeds — a hero map or video) stay eager instead of |
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// being lazy-loaded unconditionally. |
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$skip = (int) ($this->settings['lcp_skip_count'] ?? 2); |
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$position = 0; |
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|
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return preg_replace_callback('/<iframe\s[^>]*>/i', function ($matches) use ($skip, &$position) { |
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$tag = $matches[0]; |
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|
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if (preg_match('/\sloading\s*=/i', $tag)) { |
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return $tag; |
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} |
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|
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$position++; |
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if ($position <= $skip) { |
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return $this->inject_attribute($tag, 'loading', 'eager'); |
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} |
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|
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return $this->inject_attribute($tag, 'loading', 'lazy'); |
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}, $content); |
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} |
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|
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/** |
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* True when the current request renders an AMP page. The AMP runtime |
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* manages its own loading strategy and rejects foreign attributes, so |
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* this filter is skipped there. The helper indirection keeps static |
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* analysis from assuming the AMP plugin's functions always exist. |
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*/ |
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private function is_amp_request(): bool { |
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if (self::func_is_available('amp_is_request')) { |
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return (bool) amp_is_request(); |
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} |
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if (self::func_is_available('is_amp_endpoint')) { |
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return (bool) is_amp_endpoint(); |
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} |
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return false; |
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} |
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|
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private static function func_is_available(string $function): bool { |
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return function_exists($function); |
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} |
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|
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/** |
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* Inject an HTML attribute into a tag if not already present. |
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*/ |
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private function inject_attribute(string $tag, string $attr, string $value): string { |
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if (preg_match('/\s' . preg_quote($attr, '/') . '\s*=/i', $tag)) { |
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return $tag; |
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} |
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|
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return preg_replace('/\s*\/?>$/', sprintf(' %s="%s"$0', esc_attr($attr), esc_attr($value)), $tag, 1); |
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} |
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} |
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|
