Changeset 56933 for trunk/src/wp-includes/class-wp-scripts.php

Timestamp:

10/13/2023 06:44:12 PM (14 months ago)

Author:

westonruter

Message:

Script Loader: Move delayed head script to footer when there is a blocking footer dependent.

This prevents a performance regression when a blocking script is enqueued in the footer which depends on a delayed script in the head (with async or defer). In order to preserve the execution order, a delayed dependency must fall back to blocking when there is a blocking dependent. But since it was originally delayed (and thus executes similarly to a footer script), it does not need to be in the head and can be moved to the footer. This prevents blocking the critical rendering path.

Props adamsilverstein, westonruter, flixos90.
Fixes #59599.
See #12009.

File:

• trunk/src/wp-includes/class-wp-scripts.php (modified) (2 diffs)

trunk/src/wp-includes/class-wp-scripts.php

@@ -233 +233 @@
 
     /**
+     * Checks whether all dependents of a given handle are in the footer.
+     *
+     * If there are no dependents, this is considered the same as if all dependents were in the footer.
+     *
+     * @since 6.4.0
+     *
+     * @param string $handle Script handle.
+     * @return bool Whether all dependents are in the footer.
+     */
+    private function are_all_dependents_in_footer( $handle ) {
+        foreach ( $this->get_dependents( $handle ) as $dep ) {
+            if ( isset( $this->groups[ $dep ] ) && 0 === $this->groups[ $dep ] ) {
+                return false;
+            }
+        }
+        return true;
+    }
+
+    /**
      * Processes a script dependency.
      *
@@ -280 +299 @@
         if ( ! $this->is_delayed_strategy( $intended_strategy ) ) {
             $intended_strategy = '';
+        }
+
+        /*
+         * Move this script to the footer if:
+         * 1. The script is in the header group.
+         * 2. The current output is the header.
+         * 3. The intended strategy is delayed.
+         * 4. The actual strategy is not delayed.
+         * 5. All dependent scripts are in the footer.
+         */
+        if (
+            0 === $group &&
+            0 === $this->groups[ $handle ] &&
+            $intended_strategy &&
+            ! $this->is_delayed_strategy( $strategy ) &&
+            $this->are_all_dependents_in_footer( $handle )
+        ) {
+            $this->in_footer[] = $handle;
+            return false;
         }