From 2581c0829e32d30502a2e524d9bfc124aa81408e Mon Sep 17 00:00:00 2001
From: inokawa <48897392+inokawa@users.noreply.github.com>
Date: Wed, 10 Jul 2024 23:21:49 +0900
Subject: [PATCH] Improve timeout handling on imperative scroll when document
 is inactive

---
 src/core/scroller.ts | 12 +++++++++---
 src/core/store.ts    |  4 ++++
 2 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/src/core/scroller.ts b/src/core/scroller.ts
index dd48b23e6..2f34a1828 100644
--- a/src/core/scroller.ts
+++ b/src/core/scroller.ts
@@ -200,13 +200,19 @@ export const createScroller = (
     const waitForMeasurement = (): [Promise<void>, () => void] => {
       // Wait for the scroll destination items to be measured.
       // The measurement will be done asynchronously and the timing is not predictable so we use promise.
-      // For example, ResizeObserver may not fire when window is not visible.
       let queue: (() => void) | undefined;
       return [
         new Promise<void>((resolve, reject) => {
           queue = resolve;
-          // Reject when items around scroll destination completely measured
-          timeout((cancelScroll = reject), 150);
+          cancelScroll = reject;
+
+          // Resize event may not happen when the window/tab is not visible, or during browser back in Safari.
+          // We have to wait for the initial measurement to avoid failing imperative scroll on mount.
+          // https://github.com/inokawa/virtua/issues/450
+          if (store._isInitialMeasurementDone()) {
+            // Reject when items around scroll destination completely measured
+            timeout(reject, 150);
+          }
         }),
         store._subscribe(UPDATE_SIZE_EVENT, () => {
           queue && queue();
diff --git a/src/core/store.ts b/src/core/store.ts
index c0b6a34dc..895d4084f 100644
--- a/src/core/store.ts
+++ b/src/core/store.ts
@@ -117,6 +117,7 @@ export type VirtualStore = {
   _getCacheSnapshot(): CacheSnapshot;
   _getRange(): ItemsRange;
   _isUnmeasuredItem(index: number): boolean;
+  _isInitialMeasurementDone(): boolean;
   _hasUnmeasuredItemsInFrozenRange(): boolean;
   _getItemOffset(index: number): number;
   _getItemSize(index: number): number;
@@ -216,6 +217,9 @@ export const createVirtualStore = (
     _isUnmeasuredItem(index) {
       return cache._sizes[index] === UNCACHED;
     },
+    _isInitialMeasurementDone() {
+      return !!viewportSize;
+    },
     _hasUnmeasuredItemsInFrozenRange() {
       if (!_frozenRange) return false;
       return cache._sizes