fix(frontend/scroll): no callback for disconnected elements (#11714)

* fix(frontend/scroll): no callback for disconnected elements

* Update CHANGELOG.md

3 files changed, 69 insertions, 4 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index ba9fb8cbcd..12796b00f9 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -30,12 +30,13 @@
 - Fix: サーバー情報画面(`/instance-info/{domain}`)でブロックができないのを修正
 - Fix: 未読のお知らせの「わかった」をクリック・タップしてもその場で「わかった」が消えない問題を修正
 - Fix: iOSで画面を回転させるとテキストサイズが変わる問題を修正
+- Fix: タイムラインを下にスクロールしてノート画面に移動して再び戻ったら以前のスクロール位置を失う問題を修正
 
 ### Server
 - cacheRemoteFilesの初期値はfalseになりました
-- 一部のfeatured noteを照会できない問題を修正
 - ファイルアップロード時等にファイル名の拡張子を修正する関数(correctFilename)の挙動を改善
-- fix: muteがapiからのuser list timeline取得で機能しない問題を修正
+- Fix: 一部のfeatured noteを照会できない問題を修正
+- Fix: muteがapiからのuser list timeline取得で機能しない問題を修正
 
 ## 13.14.2
 
diff --git a/packages/frontend/src/scripts/scroll.ts b/packages/frontend/src/scripts/scroll.ts
index b2b2c41dcf..7338de62b6 100644
--- a/packages/frontend/src/scripts/scroll.ts
+++ b/packages/frontend/src/scripts/scroll.ts
@@ -30,7 +30,7 @@ export function getScrollPosition(el: HTMLElement | null): number {
 
 export function onScrollTop(el: HTMLElement, cb: () => unknown, tolerance = 1, once = false) {
 	// とりあえず評価してみる
-	if (isTopVisible(el)) {
+	if (el.isConnected && isTopVisible(el)) {
 		cb();
 		if (once) return null;
 	}
@@ -54,7 +54,7 @@ export function onScrollBottom(el: HTMLElement, cb: () => unknown, tolerance = 1
 	const container = getScrollContainer(el);
 
 	// とりあえず評価してみる
-	if (isBottomVisible(el, tolerance, container)) {
+	if (el.isConnected && isBottomVisible(el, tolerance, container)) {
 		cb();
 		if (once) return null;
 	}
diff --git a/packages/frontend/test/scroll.test.ts b/packages/frontend/test/scroll.test.ts
new file mode 100644
index 0000000000..3fa740b11c
--- /dev/null
+++ b/packages/frontend/test/scroll.test.ts
@@ -0,0 +1,64 @@
+/*
+ * SPDX-FileCopyrightText: syuilo and other misskey contributors
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+import { describe, test, assert, afterEach } from 'vitest';
+import { Window } from 'happy-dom';
+import { onScrollBottom, onScrollTop } from '@/scripts/scroll';
+
+describe('Scroll', () => {
+	describe('onScrollTop', () => {
+		test('Initial onScrollTop callback for connected elements', () => {
+			const { document } = new Window();
+			const div = document.createElement('div');
+			assert.strictEqual(div.scrollTop, 0);
+
+			document.body.append(div);
+
+			let called = false;
+			onScrollTop(div as any as HTMLElement, () => called = true);
+
+			assert.ok(called);
+		});
+
+		test('No onScrollTop callback for disconnected elements', () => {
+			const { document } = new Window();
+			const div = document.createElement('div');
+			assert.strictEqual(div.scrollTop, 0);
+
+			let called = false;
+			onScrollTop(div as any as HTMLElement, () => called = true);
+
+			assert.ok(!called);
+		});
+	});
+
+	describe('onScrollBottom', () => {
+		test('Initial onScrollBottom callback for connected elements', () => {
+			const { document } = new Window();
+			const div = document.createElement('div');
+			assert.strictEqual(div.scrollTop, 0);
+			(div as any).scrollHeight = 100; // happy-dom has no scrollHeight
+
+			document.body.append(div);
+
+			let called = false;
+			onScrollBottom(div as any as HTMLElement, () => called = true);
+
+			assert.ok(called);
+		});
+
+		test('No onScrollBottom callback for disconnected elements', () => {
+			const { document } = new Window();
+			const div = document.createElement('div');
+			assert.strictEqual(div.scrollTop, 0);
+			(div as any).scrollHeight = 100; // happy-dom has no scrollHeight
+
+			let called = false;
+			onScrollBottom(div as any as HTMLElement, () => called = true);
+
+			assert.ok(!called);
+		});
+	});
+});