Improve timeout handling on imperative scroll when document is inactive

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();

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