Profile redesign: Account fields grid (#37976)

app/javascript/mastodon/hooks/useObserver.ts

@@ -0,0 +1,29 @@
+import { useEffect, useRef } from 'react';
+
+export function useResizeObserver(callback: ResizeObserverCallback) {
+  const observerRef = useRef<ResizeObserver | null>(null);
+  observerRef.current ??= new ResizeObserver(callback);
+
+  useEffect(() => {
+    const observer = observerRef.current;
+    return () => {
+      observer?.disconnect();
+    };
+  }, []);
+
+  return observerRef.current;
+}
+
+export function useMutationObserver(callback: MutationCallback) {
+  const observerRef = useRef<MutationObserver | null>(null);
+  observerRef.current ??= new MutationObserver(callback);
+
+  useEffect(() => {
+    const observer = observerRef.current;
+    return () => {
+      observer?.disconnect();
+    };
+  }, []);
+
+  return observerRef.current;
+}