actually we need a proper function

packages/svelte/src/compiler/phases/3-transform/client/visitors/template.js

@@ -1139,16 +1139,20 @@ function serialize_event_handler(node, { state, visit }) {
 		handler = node.expression;
 
 		// Event handlers can be dynamic (source/store/prop/conditional etc)
-		const dynamic_handler = () => {
+		const dynamic_handler = () =>
-			return b.arrow(
+			b.function(
+				null,
 				[b.rest(b.id('$$args'))],
+				b.block([
+					b.return(
 						b.call(
 							b.member(/** @type {Expression} */ (visit(handler)), b.id('apply'), false, true),
 							b.this,
 							b.id('$$args')
 						)
+					)
+				])
 			);
-		};
 
 		if (handler.type === 'Identifier' || handler.type === 'MemberExpression') {
 			const id = object(handler);