Changeset 55847 for trunk/src/wp-includes/media.php

Timestamp:

05/22/2023 07:11:36 PM (6 months ago)

Author:

flixos90

Message:

Media: Conditionally skip lazy-loading on images before the loop to improve LCP performance.

When the logic to exclude images that likely appear above the fold from being lazy-loaded was introduced in WordPress 5.9, initially only images that appear within the main query loop were being considered. However, there is a good chance that images above the fold are rendered before the loop starts, for example in the header template part.

It is particularly common for a theme to display the featured image for a single post in the header. Based on HTTP Archive data from February 2023, the majority of LCP images that are still being lazy-loaded on WordPress sites use the wp-post-image class, i.e. are featured images.

This changeset enhances the logic in wp_get_loading_attr_default() to not lazy-load images that appear within or after the header template part and before the query loop, using a new WP_Query::$before_loop property.

For block themes, this was for the most part already addressed in [55318], however this enhancement implements the solution in a more generally applicable way that brings the improvement to classic themes as well.

Props thekt12, flixos90, spacedmonkey, costdev, zunaid321, mukesh27.
Fixes #58211.
See #53675, #56930.

File:

• trunk/src/wp-includes/media.php (modified) (4 diffs)

trunk/src/wp-includes/media.php

@@ -5491 +5491 @@
  * @since 5.9.0
  *
+ * @global WP_Query $wp_query WordPress Query object.
+ *
  * @param string $context Context for the element for which the `loading` attribute value is requested.
  * @return string|bool The default `loading` attribute value. Either 'lazy', 'eager', or a boolean `false`, to indicate
@@ -5496 +5498 @@
  */
 function wp_get_loading_attr_default( $context ) {
+    global $wp_query;
+
     // Skip lazy-loading for the overall block template, as it is handled more granularly.
     if ( 'template' === $context ) {
@@ -5502 +5506 @@
 
     // Do not lazy-load images in the header block template part, as they are likely above the fold.
+    // For classic themes, this is handled in the condition below using the 'get_header' action.
     $header_area = WP_TEMPLATE_PART_AREA_HEADER;
     if ( "template_part_{$header_area}" === $context ) {
@@ -5507 +5512 @@
     }
 
-    /*
-     * Skip programmatically created images within post content as they need to be handled together with the other
-     * images within the post content.
-     * Without this clause, they would already be counted below which skews the number and can result in the first
-     * post content image being lazy-loaded only because there are images elsewhere in the post content.
-     */
-    if ( ( 'the_post_thumbnail' === $context || 'wp_get_attachment_image' === $context ) && doing_filter( 'the_content' ) ) {
-        return false;
+    // Special handling for programmatically created image tags.
+    if ( ( 'the_post_thumbnail' === $context || 'wp_get_attachment_image' === $context ) ) {
+        /*
+         * Skip programmatically created images within post content as they need to be handled together with the other
+         * images within the post content.
+         * Without this clause, they would already be counted below which skews the number and can result in the first
+         * post content image being lazy-loaded only because there are images elsewhere in the post content.
+         */
+        if ( doing_filter( 'the_content' ) ) {
+            return false;
+        }
+
+        // Conditionally skip lazy-loading on images before the loop.
+        if (
+            // Only apply for main query but before the loop.
+            $wp_query->before_loop && $wp_query->is_main_query()
+            /*
+             * Any image before the loop, but after the header has started should not be lazy-loaded,
+             * except when the footer has already started which can happen when the current template
+             * does not include any loop.
+             */
+            && did_action( 'get_header' ) && ! did_action( 'get_footer' )
+        ) {
+            return false;
+        }
     }