fix(router): Scroll restoration should use instant scroll behavior for traversals (#64299)

atscott · AndrewKushnir · commit 6e4bcc7d22d4 · 2025-10-09T11:13:46.000-07:00
When the scroll position is being restored, this change upates the behavior to use 'instant' rather than the default 'auto', which will be whatever the browser behavior is for 'window.scrollTo'. The 'smooth' behavior does not match how browsers behavior when performing a traversal navigation for MPAs, which is 'instant'. related to #58258 PR Close #64299
diff --git a/packages/router/src/router_scroller.ts b/packages/router/src/router_scroller.ts
@@ -85,12 +85,13 @@ export class RouterScroller implements OnDestroy {
   private consumeScrollEvents() {
     return this.transitions.events.subscribe((e) => {
       if (!(e instanceof Scroll)) return;
+      const instantScroll: ScrollOptions = {behavior: 'instant'};
       // a popstate event. The pop state event will always ignore anchor scrolling.
       if (e.position) {
         if (this.options.scrollPositionRestoration === 'top') {
-          this.viewportScroller.scrollToPosition([0, 0]);
+          this.viewportScroller.scrollToPosition([0, 0], instantScroll);
         } else if (this.options.scrollPositionRestoration === 'enabled') {
-          this.viewportScroller.scrollToPosition(e.position);
+          this.viewportScroller.scrollToPosition(e.position, instantScroll);
         }
         // imperative navigation "forward"
       } else {
diff --git a/packages/router/test/router_scroller.spec.ts b/packages/router/test/router_scroller.spec.ts
@@ -96,7 +96,9 @@ describe('RouterScroller', () => {
       events.next(new NavigationStart(3, '/a', 'popstate', {navigationId: 1}));
       events.next(new NavigationEnd(3, '/a', '/a'));
       await nextScrollEvent(events);
-      expect(viewportScroller.scrollToPosition).toHaveBeenCalledWith([10, 100]);
+      expect(viewportScroller.scrollToPosition).toHaveBeenCalledWith([10, 100], {
+        behavior: 'instant',
+      });
     });
   });
 
@@ -146,7 +148,7 @@ describe('RouterScroller', () => {
       events.next(new NavigationEnd(3, '/a#anchor', '/a#anchor'));
       await nextScrollEvent(events);
       expect(viewportScroller.scrollToAnchor).not.toHaveBeenCalled();
-      expect(viewportScroller.scrollToPosition).toHaveBeenCalledWith([0, 0]);
+      expect(viewportScroller.scrollToPosition).toHaveBeenCalledWith([0, 0], {behavior: 'instant'});
     });
   });
 
