From 1843b3ff5ea75852f0f82c95f0ab2fddaeb2e378 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Grzegorz=20Zi=C3=B3=C5=82kowski?= <grzegorz@gziolo.pl>
Date: Wed, 20 Dec 2023 12:43:50 +0100
Subject: [PATCH 1/2] Modules: Load the import map polyfill when needed

---
 .../modules/class-gutenberg-modules.php       | 26 ++++++++++++-------
 1 file changed, 16 insertions(+), 10 deletions(-)

diff --git a/lib/experimental/modules/class-gutenberg-modules.php b/lib/experimental/modules/class-gutenberg-modules.php
index 0a2da03545776e..ebdc22e58e8b62 100644
--- a/lib/experimental/modules/class-gutenberg-modules.php
+++ b/lib/experimental/modules/class-gutenberg-modules.php
@@ -152,15 +152,21 @@ public static function print_module_preloads() {
 	 * import maps (https://github.com/guybedford/es-module-shims/issues/406).
 	 */
 	public static function print_import_map_polyfill() {
-		$import_map = self::get_import_map();
-		if ( ! empty( $import_map['imports'] ) ) {
-			wp_print_script_tag(
-				array(
-					'src'   => gutenberg_url( '/build/modules/importmap-polyfill.min.js' ),
-					'defer' => true,
-				)
-			);
-		}
+		$test = 'HTMLScriptElement.supports?.("importmap")';
+		$src  = gutenberg_url( '/build/modules/importmap-polyfill.min.js' );
+
+		echo (
+			// Test presence of feature...
+			'<script>( ' . $test . ' ) || ' .
+			/*
+			 * ...appending polyfill on any failures. Cautious viewers may balk
+			 * at the `document.write`. Its caveat of synchronous mid-stream
+			 * blocking write is exactly the behavior we need though.
+			 */
+			'document.write( \'<script src="' .
+			$src .
+			'"></scr\' + \'ipt>\' );</script>'
+		);
 	}
 
 	/**
@@ -273,4 +279,4 @@ function gutenberg_dequeue_module( $module_identifier ) {
 add_action( $modules_position, array( 'Gutenberg_Modules', 'print_module_preloads' ) );
 
 // Prints the script that loads the import map polyfill in the footer.
-add_action( 'wp_footer', array( 'Gutenberg_Modules', 'print_import_map_polyfill' ), 11 );
+add_action( 'wp_head', array( 'Gutenberg_Modules', 'print_import_map_polyfill' ), 11 );

From 8f5e260136bec973b3f1b60583cc16c17378cb3e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Greg=20Zi=C3=B3=C5=82kowski?= <grzegorz@gziolo.pl>
Date: Wed, 3 Jan 2024 17:20:05 +0100
Subject: [PATCH 2/2] Update
 lib/experimental/modules/class-gutenberg-modules.php

Co-authored-by: Felix Arntz <felixarntz@users.noreply.github.com>
---
 lib/experimental/modules/class-gutenberg-modules.php | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/experimental/modules/class-gutenberg-modules.php b/lib/experimental/modules/class-gutenberg-modules.php
index ebdc22e58e8b62..5aa012f8e2f2c5 100644
--- a/lib/experimental/modules/class-gutenberg-modules.php
+++ b/lib/experimental/modules/class-gutenberg-modules.php
@@ -152,7 +152,7 @@ public static function print_module_preloads() {
 	 * import maps (https://github.com/guybedford/es-module-shims/issues/406).
 	 */
 	public static function print_import_map_polyfill() {
-		$test = 'HTMLScriptElement.supports?.("importmap")';
+		$test = 'HTMLScriptElement.supports && HTMLScriptElement.supports("importmap")';
 		$src  = gutenberg_url( '/build/modules/importmap-polyfill.min.js' );
 
 		echo (