fix: prevent numerous transition/animation memory leaks (#12759)

* fix: prevent numerous transition/animation memory leaks

* address feedback

* tweak

Author: trueadm

.changeset/silly-masks-exist.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: prevent numerous transition/animation memory leaks

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

@@ -222,6 +222,8 @@ export function transition(flags, element, get_fn, get_params) {
 					1,
 					() => {
 						dispatch_event(element, 'introend');
+						// Ensure we cancel the animation to prevent leaking
+						intro?.abort();
 						intro = current_options = undefined;
 					},
 					is_both
@@ -249,6 +251,8 @@ export function transition(flags, element, get_fn, get_params) {
 					0,
 					() => {
 						dispatch_event(element, 'outroend');
+						// Ensure we cancel the animation to prevent leaking
+						outro?.abort();
 						outro = current_options = undefined;
 						fn?.();
 					},
@@ -322,16 +326,21 @@ function animate(element, options, counterpart, t2, on_finish, on_abort) {
 		// once DOM has been updated...
 		/** @type {Animation} */
 		var a;
+		var aborted = false;
 
 		queue_micro_task(() => {
+			if (aborted) return;
 			var o = options({ direction: is_intro ? 'in' : 'out' });
 			a = animate(element, o, counterpart, t2, on_finish, on_abort);
 		});
 
 		// ...but we want to do so without using `async`/`await` everywhere, so
 		// we return a facade that allows everything to remain synchronous
 		return {
-			abort: () => a.abort(),
+			abort: () => {
+				aborted = true;
+				a?.abort();
+			},
 			deactivate: () => a.deactivate(),
 			reset: () => a.reset(),
 			t: (now) => a.t(now)

playgrounds/demo/index.html

@@ -20,9 +20,6 @@
 			const component = render(App, {
 				target: document.getElementById('root')
 			});
-
-			// @ts-ignore
-			window.unmount = () => unmount(component);
 		</script>
 	</body>
 </html>