v3: code quality pass

src/hooks/useScrollSave.ts

@@ -0,0 +1,24 @@
+import { useEffect } from "react";
+
+/**
+ * Sets up a debounced scroll listener that calls `onSave(scrollY)` when the
+ * user scrolls, but only while `enabled` is true (e.g. the page is loaded).
+ */
+export function useScrollSave(
+  enabled: boolean,
+  onSave: (scrollY: number) => void,
+) {
+  useEffect(() => {
+    if (!enabled) return;
+    let timer: ReturnType<typeof setTimeout>;
+    const onScroll = () => {
+      clearTimeout(timer);
+      timer = setTimeout(() => onSave(globalThis.scrollY), 100);
+    };
+    globalThis.addEventListener("scroll", onScroll, { passive: true });
+    return () => {
+      globalThis.removeEventListener("scroll", onScroll);
+      clearTimeout(timer);
+    };
+  }, [enabled, onSave]);
+}