Add polyfill

lib/experimental/interactivity-api/modules.php

@@ -18,6 +18,18 @@ function gutenberg_register_interactivity_module() {
 			'version' => defined( 'GUTENBERG_VERSION' ) ? GUTENBERG_VERSION : get_bloginfo( 'version' ),
 		)
 	);
+
+	// TODO: Move this to a local file and replace with a simpler version that
+	// only provides support for import maps.
+	wp_enqueue_script(
+		'es-module-shims',
+		'https://ga.jspm.io/npm:[email protected]/dist/es-module-shims.js',
+		array(),
+		null,
+		array(
+			'strategy' => 'defer',
+		)
+	);
 }
 
 add_action( 'wp_enqueue_scripts', 'gutenberg_register_interactivity_module' );