fix: improve dynamic event handling (#12570)

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

@@ -1148,25 +1148,7 @@ function serialize_event_handler(node, metadata, { state, visit }) {
 				])
 			);
 
-		if (handler.type === 'Identifier' || handler.type === 'MemberExpression') {
+		if (
-			const id = object(handler);
-			const binding = id === null ? null : state.scope.get(id.name);
-			if (
-				binding !== null &&
-				(binding.kind === 'state' ||
-					binding.kind === 'frozen_state' ||
-					binding.declaration_kind === 'import' ||
-					binding.kind === 'legacy_reactive' ||
-					binding.kind === 'derived' ||
-					binding.kind === 'prop' ||
-					binding.kind === 'bindable_prop' ||
-					binding.kind === 'store_sub')
-			) {
-				handler = dynamic_handler();
-			} else {
-				handler = /** @type {Expression} */ (visit(handler));
-			}
-		} else if (
 			metadata?.contains_call_expression &&
 			!(
 				(handler.type === 'ArrowFunctionExpression' || handler.type === 'FunctionExpression') &&
@@ -1193,6 +1175,24 @@ function serialize_event_handler(node, metadata, { state, visit }) {
 					)
 				])
 			);
+		} else if (handler.type === 'Identifier' || handler.type === 'MemberExpression') {
+			const id = object(handler);
+			const binding = id === null ? null : state.scope.get(id.name);
+			if (
+				binding !== null &&
+				(binding.kind === 'state' ||
+					binding.kind === 'frozen_state' ||
+					binding.declaration_kind === 'import' ||
+					binding.kind === 'legacy_reactive' ||
+					binding.kind === 'derived' ||
+					binding.kind === 'prop' ||
+					binding.kind === 'bindable_prop' ||
+					binding.kind === 'store_sub')
+			) {
+				handler = dynamic_handler();
+			} else {
+				handler = /** @type {Expression} */ (visit(handler));
+			}
 		} else if (handler.type === 'ConditionalExpression' || handler.type === 'LogicalExpression') {
 			handler = dynamic_handler();
 		} else {

packages/svelte/tests/runtime-runes/samples/dynamic-element-event-handler/_config.js

@@ -0,0 +1,26 @@
+import { test } from '../../test';
+
+export default test({
+	html: '<button>Tama</button><button>Pochi</button><br><button>Change Function</button>',
+
+	test({ assert, logs, target }) {
+		const [b1, b2, b3] = target.querySelectorAll('button');
+
+		b1?.click();
+		b2?.click();
+		b3?.click();
+		b1?.click();
+		b2?.click();
+
+		assert.deepEqual(logs, [
+			'creating "Hello" handler for Tama',
+			'Hello Tama',
+			'creating "Hello" handler for Pochi',
+			'Hello Pochi',
+			'creating "Bye" handler for Tama',
+			'Bye Tama',
+			'creating "Bye" handler for Pochi',
+			'Bye Pochi'
+		]);
+	}
+});

packages/svelte/tests/runtime-runes/samples/dynamic-element-event-handler/main.svelte

@@ -0,0 +1,19 @@
+<script>
+	let saySomething = $state(name => {
+		console.log('creating "Hello" handler for ' + name);
+		return { handler: () => console.log('Hello ' + name) };
+	});
+
+	function change() {
+		saySomething = name => {
+			console.log('creating "Bye" handler for ' + name);
+			return { handler: () => console.log('Bye ' + name) };
+		}
+	}
+</script>
+
+<button onclick={saySomething('Tama').handler}>Tama</button>
+<button onclick={saySomething('Pochi').handler}>Pochi</button>
+
+<br>
+<button onclick={change}>Change Function</button>