From 39af300422370995f6f96460f4bbb08144ee4e06 Mon Sep 17 00:00:00 2001
From: Serhii Kulykov <iamkulykov@gmail.com>
Date: Thu, 5 Dec 2024 15:03:23 +0200
Subject: [PATCH] fix: use Math.round to get correct scroller first index
 (#8278)

---
 .../date-picker/src/vaadin-infinite-scroller.js   |  3 ++-
 packages/date-picker/test/scroller.test.js        | 15 +++++++++++++++
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/packages/date-picker/src/vaadin-infinite-scroller.js b/packages/date-picker/src/vaadin-infinite-scroller.js
index 0dc62272cc..d04f40c10a 100644
--- a/packages/date-picker/src/vaadin-infinite-scroller.js
+++ b/packages/date-picker/src/vaadin-infinite-scroller.js
@@ -376,7 +376,8 @@ class InfiniteScroller extends PolymerElement {
 
   /** @private */
   _updateClones(viewPortOnly) {
-    this._firstIndex = ~~((this._buffers[0].translateY - this._initialScroll) / this.itemHeight) + this._initialIndex;
+    this._firstIndex =
+      Math.round((this._buffers[0].translateY - this._initialScroll) / this.itemHeight) + this._initialIndex;
 
     const scrollerRect = viewPortOnly ? this.$.scroller.getBoundingClientRect() : undefined;
     this._buffers.forEach((buffer, bufferIndex) => {
diff --git a/packages/date-picker/test/scroller.test.js b/packages/date-picker/test/scroller.test.js
index d808674aa1..0cbea53350 100644
--- a/packages/date-picker/test/scroller.test.js
+++ b/packages/date-picker/test/scroller.test.js
@@ -118,3 +118,18 @@ describe('vaadin-infinite-scroller', () => {
     });
   });
 });
+
+describe('fractional item size', () => {
+  let scroller;
+
+  beforeEach(async () => {
+    scroller = fixtureSync('<vaadin-infinite-scroller></vaadin-infinite-scroller>');
+    scroller.bufferSize = 80;
+    scroller.style.setProperty('--vaadin-infinite-scroller-item-height', '30.0001px');
+    await activateScroller(scroller);
+  });
+
+  it('should be at the position 0', () => {
+    expect(scroller.position).to.be.closeTo(0, 0.001);
+  });
+});