edge case

packages/svelte/src/internal/client/dom/elements/transitions.js

@@ -174,7 +174,7 @@ export function bind_transition(element, get_fn, get_params, direction, global)
 
 			if (!current_options?.duration) {
 				current_options = null;
-				callback?.();
+				callback();
 				return;
 			}
 
@@ -207,7 +207,7 @@ export function bind_transition(element, get_fn, get_params, direction, global)
 					.then(() => {
 						p = target;
 						current_animation = current_options = null;
-						callback?.();
+						callback();
 					})
 					.catch(noop);
 			} else if (tick) {
@@ -238,6 +238,8 @@ export function bind_transition(element, get_fn, get_params, direction, global)
 				});
 
 				current_options = null;
+			} else {
+				setTimeout(callback, duration);
 			}
 		}
 	};

packages/svelte/src/internal/client/types.d.ts

@@ -345,7 +345,7 @@ export type ProxyStateObject<T = Record<string | symbol, any>> = T & {
 // happy we don't need them, and rename this
 export interface Transition2 {
 	global: boolean;
-	to(target: number, callback?: () => void): void;
+	to(target: number, callback: () => void): void;
 }
 
 export * from './reactivity/types';