drive-by, fix #13019

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

@@ -188,7 +188,9 @@ export function transition(flags, element, get_fn, get_params) {
 		// If a transition is still ongoing, we use the existing options rather than generating
 		// new ones. This ensures that reversible transitions reverse smoothly, rather than
 		// jumping to a new spot because (for example) a different `duration` was used
-		return (current_options ??= get_fn()(element, get_params?.(), { direction }));
+		return (current_options ??= get_fn()(element, get_params?.() ?? /** @type {P} */ ({}), {
+			direction
+		}));
 	}
 
 	/** @type {TransitionManager} */

packages/svelte/tests/runtime-legacy/samples/transition-js-deferred-b/main.svelte

@@ -4,7 +4,7 @@
 	let foo_text;
 	let bar_text;
 
-	function foo(node, params) {
+	function foo(node, { duration = 100 }) {
 		foo_text = node.textContent;
 
 		return () => {
@@ -13,7 +13,7 @@
 			}
 
 			return {
-				duration: 100,
+				duration,
 				tick: t => {
 					node.foo = t;
 				}
@@ -21,7 +21,7 @@
 		};
 	}
 
-	function bar(node, params) {
+	function bar(node, { duration = 100 }) {
 		bar_text = node.textContent;
 
 		return () => {
@@ -30,7 +30,7 @@
 			}
 
 			return {
-				duration: 100,
+				duration,
 				tick: t => {
 					node.foo = t;
 				}
@@ -43,4 +43,4 @@
 	<div class="foo" in:foo>a</div>
 {:else}
 	<div out:bar>b</div>
-{/if}
+{/if}