Changeset 60931 for trunk/src/wp-includes/script-modules.php

Timestamp:

10/14/2025 05:45:17 AM (3 months ago)

Author:

westonruter

Message:

Script Loader: Propagate fetchpriority from dependents to dependencies.

This introduces a "fetchpriority bumping" mechanism for both classic scripts (WP_Scripts) and script modules (WP_Script_Modules). When a script with a higher fetchpriority is enqueued, any of its dependencies will have their fetchpriority elevated to match that of the highest-priority dependent. This ensures that all assets in a critical dependency chain are loaded with the appropriate priority, preventing a high-priority script from being blocked by a low-priority dependency. This is similar to logic used in script loading strategies to ensure that a blocking dependent causes delayed (async/defer) dependencies to also become blocking. See #12009.

When a script's fetchpriority is escalated, its original, registered priority is added to the tag via a data-wp-fetchpriority attribute. This matches the addition of the data-wp-strategy parameter added when the resulting loading strategy does not match the original.

Developed in ​https://github.com/WordPress/wordpress-develop/pull/9770.

Follow-up to [60704].

Props westonruter, jonsurrell.
Fixes #61734.

File:

• trunk/src/wp-includes/script-modules.php (modified) (1 diff)

trunk/src/wp-includes/script-modules.php

@@ -182 +182 @@
         }
 
-        // The Interactivity API is designed with server-side rendering as its primary goal, so all of its script modules should be loaded with low fetch priority since they should not be needed in the critical rendering path.
+        /*
+         * The Interactivity API is designed with server-side rendering as its primary goal, so all of its script modules
+         * should be loaded with low fetchpriority since they should not be needed in the critical rendering path.
+         * Also, the @wordpress/a11y script module is intended to be used as a dynamic import dependency, in which case
+         * the fetchpriority is irrelevant. See <https://make.wordpress.org/core/2024/10/14/updates-to-script-modules-in-6-7/>.
+         * However, in case it is added as a static import dependency, the fetchpriority is explicitly set to be 'low'
+         * since the module should not be involved in the critical rendering path, and if it is, its fetchpriority will
+         * be bumped to match the fetchpriority of the dependent script.
+         */
         $args = array();
-        if ( str_starts_with( $script_module_id, '@wordpress/interactivity' ) || str_starts_with( $script_module_id, '@wordpress/block-library' ) ) {
+        if (
+            str_starts_with( $script_module_id, '@wordpress/interactivity' ) ||
+            str_starts_with( $script_module_id, '@wordpress/block-library' ) ||
+            '@wordpress/a11y' === $script_module_id
+        ) {
             $args['fetchpriority'] = 'low';
         }