fix: ensure transition errors are not swallowed (#11039)

* fix: ensure transition errors are not swallowed

* feedback

Author: trueadm

.changeset/new-brooms-grin.md

@@ -0,0 +1,5 @@
+---
+"svelte": patch
+---
+
+fix: ensure transition errors are not swallowed

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

@@ -301,7 +301,17 @@ function animate(element, options, counterpart, t2, callback) {
 			.then(() => {
 				callback?.();
 			})
-			.catch(noop);
+			.catch((e) => {
+				// Error for DOMException: The user aborted a request. This results in two things:
+				// - startTime is `null`
+				// - currentTime is `null`
+				// We can't use the existence of an AbortError as this error and error code is shared
+				// with other Web APIs such as fetch().
+
+				if (animation.startTime !== null && animation.currentTime !== null) {
+					throw e;
+				}
+			});
 	} else {
 		// Timer
 		if (t1 === 0) {

packages/svelte/tests/animation-helpers.js

@@ -42,6 +42,7 @@ class Animation {
 	#cancelled = () => {};
 
 	currentTime = 0;
+	startTime = 0;
 
 	/**
 	 * @param {HTMLElement} target
@@ -122,7 +123,10 @@ class Animation {
 		if (this.currentTime > 0 && this.currentTime < this.#duration) {
 			this.#apply_keyframe(0);
 		}
-
+		// @ts-ignore
+		this.currentTime = null;
+		// @ts-ignore
+		this.startTime = null;
 		this.#cancelled();
 		raf.animations.delete(this);
 	}