From 27de1cd01dab8e4718b413f5fe11043e2be8df63 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Samy=20Pess=C3=A9?= <samypesse@gmail.com>
Date: Tue, 25 Mar 2025 15:39:45 +0100
Subject: [PATCH] Default to the first ID as being active in scroll detection
 (#3036)

---
 packages/gitbook/src/components/hooks/useScrollActiveId.ts | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/packages/gitbook/src/components/hooks/useScrollActiveId.ts b/packages/gitbook/src/components/hooks/useScrollActiveId.ts
index 96b986eac..eacfdcc26 100644
--- a/packages/gitbook/src/components/hooks/useScrollActiveId.ts
+++ b/packages/gitbook/src/components/hooks/useScrollActiveId.ts
@@ -12,11 +12,12 @@ export function useScrollActiveId(
 ) {
     const { rootMargin, threshold = 0.5 } = options;
 
-    const [activeId, setActiveId] = React.useState<string | null>(null);
+    const [activeId, setActiveId] = React.useState<string>(ids[0]);
     const sectionsIntersectingMap = React.useRef<Map<string, boolean>>(new Map());
 
     React.useEffect(() => {
-        setActiveId(null);
+        const defaultActiveId = ids[0];
+        setActiveId((activeId) => (ids.indexOf(activeId) !== -1 ? activeId : defaultActiveId));
 
         if (typeof IntersectionObserver === 'undefined') {
             return;