Refresh thread replies periodically & when refocusing window (#36547)

app/javascript/mastodon/hooks/useIsDocumentVisible.ts

@@ -0,0 +1,32 @@
+import { useEffect, useRef, useState } from 'react';
+
+export function useIsDocumentVisible({
+  onChange,
+}: {
+  onChange?: (isVisible: boolean) => void;
+} = {}) {
+  const [isDocumentVisible, setIsDocumentVisible] = useState(
+    () => document.visibilityState === 'visible',
+  );
+
+  const onChangeRef = useRef(onChange);
+  useEffect(() => {
+    onChangeRef.current = onChange;
+  }, [onChange]);
+
+  useEffect(() => {
+    function handleVisibilityChange() {
+      const isVisible = document.visibilityState === 'visible';
+
+      setIsDocumentVisible(isVisible);
+      onChangeRef.current?.(isVisible);
+    }
+    window.addEventListener('visibilitychange', handleVisibilityChange);
+
+    return () => {
+      window.removeEventListener('visibilitychange', handleVisibilityChange);
+    };
+  }, []);
+
+  return isDocumentVisible;
+}