Ensure interactivity scripts remain in footer in WP<6.3

lib/experimental/interactivity-api/scripts.php

@@ -7,21 +7,32 @@
  */
 
 /**
- * Move interactive scripts to the footer and make them load with the defer strategy.
- * This ensures they work with `wp_store`.
+ * Makes sure that interactivity scripts execute after all `wp_store` directives have been printed to the page.
+ *
+ * In WordPress 6.3+ this is achieved by printing in the head but marking the scripts with defer. This has the benefit
+ * of early discovery so the script is loaded by the browser, while at the same time not blocking rendering. In older
+ * versions of WordPress, this is achieved by loading the scripts in the footer.
+ *
+ * @link https://make.wordpress.org/core/2023/07/14/registering-scripts-with-async-and-defer-attributes-in-wordpress-6-3/
  */
 function gutenberg_interactivity_move_interactive_scripts_to_the_footer() {
-	// Move the @wordpress/interactivity package to the footer.
-	wp_script_add_data( 'wp-interactivity', 'group', 1 );
-	wp_script_add_data( 'wp-interactivity', 'strategy', 'defer' );
+	$supports_defer = version_compare( strtok( get_bloginfo( 'version' ), '-' ), '6.3', '>=' );
+	if ( $supports_defer ) {
+		// Defer execution of @wordpress/interactivity package but continue loading in head.
+		wp_script_add_data( 'wp-interactivity', 'strategy', 'defer' );
+		wp_script_add_data( 'wp-interactivity', 'group', 0 );
+	} else {
+		// Move the @wordpress/interactivity package to the footer.
+		wp_script_add_data( 'wp-interactivity', 'group', 1 );
+	}
 
 	// Move all the view scripts of the interactive blocks to the footer.
 	$registered_blocks = \WP_Block_Type_Registry::get_instance()->get_all_registered();
 	foreach ( array_values( $registered_blocks ) as $block ) {
 		if ( isset( $block->supports['interactivity'] ) && $block->supports['interactivity'] ) {
 			foreach ( $block->view_script_handles as $handle ) {
-				wp_script_add_data( $handle, 'group', 1 );
-				wp_script_add_data( $handle, 'strategy', 'defer' );
+				// Note that all block view scripts are already made defer by default.
+				wp_script_add_data( $handle, 'group', $supports_defer ? 0 : 1 );
 			}
 		}
 	}