first commit

common/resources/client/utils/hooks/sticky-sentinel.ts

@@ -0,0 +1,22 @@
+import {useCallback, useRef, useState} from 'react';
+
+export function useStickySentinel() {
+  const [isSticky, setIsSticky] = useState(false);
+
+  const observerRef = useRef<IntersectionObserver>();
+
+  const sentinelRef = useCallback((sentinel: HTMLDivElement | null) => {
+    if (sentinel) {
+      const observer = new IntersectionObserver(
+        ([e]) => setIsSticky(e.intersectionRatio < 1),
+        {threshold: [1]}
+      );
+      observerRef.current = observer;
+      observer.observe(sentinel);
+    } else if (observerRef.current) {
+      observerRef.current?.disconnect();
+    }
+  }, []);
+
+  return {isSticky, sentinelRef};
+}