122 Commits

Author SHA1 Message Date
nk
bb40d26621 chore: bump backend submodule (compose: конфиг авто-обновления) 2026-06-07 19:27:36 +03:00
nk
9828bdf8d1 chore(app): bump версии до 6 / 1.5 (релиз: распознавание Shazam + история) 2026-06-07 19:22:06 +03:00
nk
bdeb57c2ad fix(app): кнопка распознавания видна и при пустом исполнителе трека
track == null почти не выполнялось: «безымянные» станции шлют ICY-строку без
разделителя → parseIcyTitle делает трек с пустым artist. Показываем кнопку, когда
нет РЕАЛЬНОГО трека (track null ИЛИ пустой artist/song ИЛИ song == имя станции).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-07 18:59:46 +03:00
nk
38ddc96fab feat(app): сообщение «слишком много запросов» (429) при распознавании
Bump backend submodule (глобальный лимит распознаваний).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-07 18:47:38 +03:00
nk
c0ee47b699 fix(app): таймаут 30с для запроса распознавания Shazam
Бэкенд-распознавание асинхронное (чанк аудио + поллинг ~до 18с) — точечно
поднимаем readTimeout до 30с только для пути shazam/recognize (базовый 10с мал).
Bump backend submodule (двухстадийный флоу shazam-api.com).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-07 18:45:08 +03:00
nk
69682268f3 feat(app): кнопка «Распознать трек» (Shazam) + история распознанных
- кнопка распознавания в плеере: видна только на музыкальных станциях без
  метаданных эфира (track == null), показывает спиннер и результат через Toast
- распознанный трек отображается в плеере и пишется в ОТДЕЛЬНУЮ историю
  распознанных (не дублируется в историю эфирных треков — гейт по ключу)
- экран Истории: переключатель «Треки эфира | Распознанные», два списка
- Room: таблица recognized_track (миграция 7→8), DAO/репозиторий
- ShazamRepository → POST /shazam/recognize/{stationId}, маппинг 503/400 в текст
- MusicGenres.isMusicStation — клиентский гейт (синхронизирован с бэкендом)
- bump backend submodule (модуль shazam)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-07 18:38:17 +03:00
nk
251809df33 fix(filters): уменьшение чипа только у кнопки (offset=0 в покое = полный)
Баг: offset первого чипа в покое = 0 (считается от начала контента, не от вьюпорта),
а формула ждала offset≥235px → «Все» и соседние были невидимы/крошечные через пол-экрана.
Фикс: recedeFactor = info.offset / shrinkPx + 1 — полный размер в покое и правее (offset≥0),
уменьшение/затухание ТОЛЬКО когда чип уезжает влево под кнопку (offset<0, зона ~32dp).
Отступ-зазор уменьшен 96→60dp (Радио) / 100→64dp (Чарты) — «Все» вплотную к кнопке.
2026-06-07 17:55:11 +03:00
nk
8b1c65fa43 feat(filters): чип уменьшается и тает у кнопки (эффект отдаления в глубину)
Вместо простого затухания края — per-chip трансформация по позиции: чип масштабируется
0.42..1 + alpha по recedeFactor (offset элемента в LazyRow: правее 92dp — норма, к 46dp —
исчез). transformOrigin центр-лево → будто уходит в глубину под кнопку-категорию.
Отступ слева увеличен (взлётка под кнопкой 96/100dp). Радио и Чарты.
2026-06-07 17:43:10 +03:00
nk
87dca7a6df feat(filters): чипы растворяются под кнопкой-категорией (fade left edge)
Кнопка-категории теперь ПОВЕРХ чипов (Box-оверлей), чипы идут во всю ширину с
отступом слева под кнопку. У левого края — затухание прозрачности (Modifier.
fadingStartEdge: graphicsLayer Offscreen + horizontalGradient BlendMode.DstIn), так
чипы при прокрутке влево красиво уплывают под кнопку и растворяются, а не обрезаются.
FilterChips/GenreSelector получили параметр contentPadding. Экраны Радио и Чарты.
2026-06-07 17:33:35 +03:00
nk
78282e97ca feat(filters): быстрый выбор категории + очистка поиска
- Кнопка-«категории» (круглая, акцентная рамка, иконка SlidersHorizontal) СЛЕВА от
  чипа «Все» — на экранах Радио и Чарты. Открывает шторку со списком всех категорий
  (Радио — жанры, Чарты — стили) + поиск, чтобы не листать чипы. CategoryPicker —
  переиспользуемый компонент с поиском и отметкой выбранного.
- SearchBar: анимированная кнопка очистки (X, scale+fade появление, haptic) при
  непустом запросе.
2026-06-07 17:25:12 +03:00
nk
645c2f14db fix(nav): анимация иконки заметнее — медленнее и с отскоком (spring 0.36/240) 2026-06-07 17:08:55 +03:00
nk
a5d9a06c3f feat(nav+fav): порядок меню, анимация иконки при выборе, индикатор на избранном
- Порядок нижнего меню: Радио · Избранное · История · Чарты · Запись · Настройки.
- Иконка вкладки при выборе делает упругий scale-«поп» (spring MediumBouncy) —
  в нижнем баре и боковом рейле.
- На экране «Избранное» играющая станция теперь подсвечивается так же, как на
  главной: вращающееся свечение под обложкой + индикатор-эквалайзер в углу
  (FavoritesViewModel отдаёт playingStationId/isPlaying из PlayerController,
  FavoritesScreen передаёт isCurrent/isPlaying в StationCard).
2026-06-07 17:06:28 +03:00
nk
d63c1d4187 feat(splash+icon): фон иконки-градиент под тему + темо-зависимый сплэш
- Подложка adaptive-иконки: градиент под акцент темы + радиальное свечение + мягкая
  тень от логотипа (ic_bg_<тема>, было плоским цветом). Иконку-лого не трогал.
- Сплэш под выбранную тему: системный сплэш Android 12+ нельзя перекрасить под выбор
  пользователя (alias-тема на ColorOS игнорится), поэтому системный = просто тёмный
  (splash_transparent), а красивый сплэш рисуем сами на Compose (SplashOverlay):
  3D-лого + акцентное свечение + тень + анимация, цвет берём из текущей темы.
- Тему на старте читаем синхронно из SharedPreferences (мгновенно, без блокировки кадра).
- Ускорен холодный старт до первого кадра 1.48с→1.11с: сплэш рисуется на первом
  дешёвом кадре, тяжёлый контент (ViewModels/плеер) композится под ним; старт
  PlayerService уведён с критического пути. Остаток — оверхед debug-сборки.
2026-06-07 16:57:01 +03:00
nk
01729e0a52 fix(brand): отступы лого в иконке + новый логотип на сплэше
- ic_fg_<тема> уменьшены (196/432) — у логотипа появились поля от краёв подложки.
- splash: windowSplashScreenAnimatedIcon → @drawable/splash_logo (новая монограмма,
  forest-цвет, т.к. сплэш показывается до загрузки темы); было @mipmap/ic_launcher.
- дефолтная ic_launcher/round переведена на новый forest-логотип (недавние/настройки).
2026-06-07 16:22:47 +03:00
nk
2fcc065a18 feat(brand): новый 3D-логотип (монограмма R) + лого/иконка под цветовую тему
Логотип: монограмма-R пользователя отрендерена в матовый 3D через routerai
(gpt-5.4-image), один мастер перекрашен под 8 тем (recolor по яркости, форма
идентична).
- Внутри приложения: AppMark показывает перекрашенный 3D-логотип текущей палитры
  (LocalThemePalette + ThemePalette.logoRes, drawable logo_<тема>).
- Иконка лаунчера следует теме: 8 adaptive-иконок (ic_fg_<тема> + ic_bg_<тема>) и
  8 activity-alias в манифесте; LauncherIconManager включает alias выбранной темы,
  гасит остальные (ровно один активен, guard против лишних миганий). Переключение —
  в MainActivity по LaunchedEffect(paletteId). На ColorOS иконка может обновляться
  с задержкой — особенность системы.
Скрипты генерации в design/logos (ключ routerai — вне репо, ~/.routerai_key).
2026-06-07 16:17:39 +03:00
nk
07f56acf27 fix(player): фон не глохнет — запрос уведомлений + исключение из оптимизации батареи
На OnePlus/ColorOS радио глохло в фоне даже с wake mode. Причины: POST_NOTIFICATIONS
не выдан (медиа-уведомление не показывалось → foreground-сервис хрупкий) и
приложение не в вайтлисте Doze. MainActivity на старте запрашивает POST_NOTIFICATIONS
(13+), затем системный диалог REQUEST_IGNORE_BATTERY_OPTIMIZATIONS (один раз).
v1.4 / versionCode 5 (clean-сборка).
2026-06-07 14:42:00 +03:00
nk
69f48d235e fix(release): v1.3 (versionCode 4) clean-сборка — лечит зацикливание обновления
Причина петли: при bump 2→3 инкрементальная сборка НЕ пересобрала BuildConfig.dex —
в v3 APK manifest versionCode=3, но BuildConfig.VERSION_CODE остался 2. Приложение
сравнивало manifest(3) > BuildConfig(2) → всегда предлагало обновиться, ставило
тот же v3, снова предлагало. Фикс: ./gradlew clean перед сборкой релиза —
BuildConfig теперь совпадает с versionCode. Проверено на телефоне: v4, диалога нет.
2026-06-07 14:29:26 +03:00
nk
44807c9dba chore(release): v1.2 (versionCode 3) — фоновое воспроизведение, эквалайзер, темы 2026-06-07 12:37:01 +03:00
nk
6eb614a729 fix(player): не глохнуть в фоне (wake mode) + авто-переподключение потока
Симптом: по Bluetooth в машине с выключенным экраном радио через время замолкало.
Причины и фиксы:
- setWakeMode(C.WAKE_MODE_NETWORK) + право WAKE_LOCK — ExoPlayer держит partial
  wakelock + wifilock во время игры. Без этого система усыпляла CPU/Wi-Fi при
  выключенном экране → буфер пустел → поток глох (главная причина).
- onPlayerError → scheduleReconnect(): при обрыве сети (туннели, край соты) поток
  пере-готавливается с нарастающей задержкой (2с→15с, до 10 попыток), а не
  замолкает навсегда. Счётчик сбрасывается при успешном старте; переподключение
  отменяется при ручной паузе/стопе/смене станции.
2026-06-07 12:35:07 +03:00
nk
e736c2393f feat(eq): настоящий эквалайзер + улучшайзеры звука (audiofx)
Раньше пресет эквалайзера в настройках был косметикой (лежал в DataStore, к звуку
не подключён). Теперь — реальные системные эффекты на фикс. аудиосессии плеера:
- AudioEffectsController: графический Equalizer (полосы устройства), BassBoost,
  Virtualizer (объём), LoudnessEnhancer (громкость тихих, до +12 дБ). Привязка к
  generateAudioSessionId() в PlayerController, переживает смену станций. Применение
  в реальном времени, сохранение в DataStore (commit на отпускании слайдера).
- Отдельный экран EqualizerScreen (Настройки → ЗВУК → Эквалайзер): тумблер,
  системные пресеты + «Свой», слайдеры полос (±дБ), bass/virtualizer/loudness.
- Эффекты best-effort: при отсутствии поддержки блок недоступен (null), UI скрывает.
- Убран фейковый чип-пресет Flat/Rock/Pop/Jazz/Bass.
2026-06-06 21:14:38 +03:00
nk
0c01eaab2d feat(update): авто-обновление APK (как в nkVPN)
UpdateManager: на старте дёргает /app-version, при version_code > BuildConfig.
VERSION_CODE показывает UpdateDialog. Скачивает APK во внутр. Download, сверяет
SHA-256 (защита от подмены по HTTP/битой загрузки), ставит через системный
установщик (FileProvider). force_update делает диалог необкрываемым. versionCode
1→2, versionName 1.0→1.1. Добавлено право REQUEST_INSTALL_PACKAGES, путь в file_paths.
2026-06-06 20:21:55 +03:00
nk
ed926e0a9d feat(theme): выбор цветовой темы (8 палитр) в настройках
8 тёмных палитр (Лес/Океан/Закат/Аметист/Неон/Янтарь/Лёд/Роза) в Palettes.kt.
RadiolaColors теперь несёт все токены + градиент; RadiolaTheme(palette) строит из
неё и RadiolaColors, и Material ColorScheme — всё приложение берёт цвета через
RadiolaTheme.colors, поэтому смена палитры перекрашивает мгновенно. Бренд-марка
(AppMark/Wordmark) тоже следует теме. Выбор в DataStore (theme_palette, дефолт
forest), читается в MainActivity и подаётся в тему. Секция «ТЕМА ОФОРМЛЕНИЯ» в
настройках — горизонтальный ряд свотчей с превью (фон+акцент+градиент).
2026-06-06 19:11:33 +03:00
nk
d9acc0efb4 fix(sleep): звук сна вплывает в конце таймера, а не в первые 90 секунд
Было: при таймере со звуком радио кроссфейдилось в шум в НАЧАЛЕ (CROSSFADE_MS=90с),
и для 15-мин таймера уже через ~1.5 мин играл полный белый шум всё оставшееся время.

Стало: радио играет почти весь таймер; в последние SOUND_OUTRO_MS (3 мин, но не
больше половины таймера) включается звук сна — радио кроссфейдится в шум, шум держится,
в самом конце затухает в тишину. Генератор шума стартует лениво (только в аутро, не
молотит весь таймер). Засыпаешь под радио, а не под резкий шум сразу.
2026-06-06 18:21:04 +03:00
nk
84c2b33473 perf(android): ленивый плеер записей, O(n) merge каталога, @Immutable, лог только в debug
- RecordingPlaybackController: ExoPlayer создаётся лениво (на первый play) и
  освобождается в stop() — раньше второй плеер висел в памяти всю сессию у каждого.
  Поллер позиции 500мс крутится только во время игры (был вечный 2 Гц main-loop).
- StationRepositoryImpl.refreshStations: merge каталога O(n) через apiById/apiByName
  индексы вместо .find на каждую станцию (было O(n²) ~700×700 на холодном старте).
  Убраны verbose Log.d-трейсы (оставлен Log.e/.w на ошибки).
- Track/Station/StreamQuality помечены @Immutable — read-only модели, иначе
  списки tags/qualities делали класс нестабильным → лишние рекомпозиции списков.
- HttpLoggingInterceptor только при BuildConfig.DEBUG (включён buildConfig feature):
  в релизе нет оверхеда на каждый запрос и утечки URL в logcat.
2026-06-06 17:13:48 +03:00
nk
f423344d13 perf(android): батарея и плавность — gate FFT, изоляция рекомпозиции, поллинг на паузе
- AudioSpectrumAnalyzer: FFT считается ТОЛЬКО когда открыт плеер (флаг active);
  раньше ~86 FFT/с молотили всегда при проигрывании (даже экран выкл) — главный
  пожиратель батареи. Включается из VisualizerHost через DisposableEffect.
- Спектр (45/с) собирается в leaf VisualizerHost, а не на верху PlayerBottomSheet —
  весь плеер больше не рекомпозится 45 раз/сек.
- now-playing поллинг (5с) останавливается на паузе (isPlaying.collectLatest) —
  раньше на паузе зря дёргали сеть каждые 5с.
- PlayerService.onDestroy отменяет serviceScope (singleton-плеер НЕ релизим).
- refreshStations (парс ~700 станций + сеть + Room) уведён на Dispatchers.IO с
  главного потока (jank/ANR на старте).
- Coil ImageLoader: память 25% + диск 100МБ (обложки не перекачиваются каждую сессию).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-06 16:33:00 +03:00
nk
861b0e2b8f feat: будильник с радиостанцией + выбор битрейта по умолчанию
Будильник (Settings → Будильник): несколько будильников, время, станция, дни недели,
fade-in пробуждения. AlarmManager.setAlarmClock (вне doze) + фолбэк, BootReceiver
перепланирует после перезагрузки, AlarmReceiver→PlayerService (foreground) →
PlayerController.startAlarmPlayback (нарастание громкости). Room: AlarmEntity/Dao, БД v7.
Выбор битрейта по умолчанию в Settings (Авто/Эконом/Стандарт/Высокое) → preferredBitrate.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-06 15:25:42 +03:00
nk
4411d53a6c feat(player): звуки для сна (белый/розовый/коричневый шум) + Smart Sleep Fade
SleepSoundPlayer — процедурная генерация цветного шума через AudioTrack (розовый —
фильтр Келлета, коричневый — random walk). В таймере сна выбор звука: радио плавно
перетекает в выбранный шум (кроссфейд ≤90с), шум играет, к концу затухает — как в
спеке («Smart Sleep Fade»). В шторке таймера — чипы выбора звука.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-06 15:08:32 +03:00
nk
bda2c5b30f feat(player): таймер сна с плавным затуханием (fade-out)
P0-фича из спеки. PlayerController: startSleepTimer/cancelSleepTimer — в последние
20с экспоненциальный fade-out громкости (frac^2), затем пауза + возврат громкости.
В плеере — пилюля «Таймер сна» (иконка Moon): при активном показывает остаток
M:SS акцентом. Шторка с интервалами 15/30/45/60/90/120 мин + «Выключить».

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-06 10:08:54 +03:00
nk
29cbe8997f feat(stations): убран чип «Новый год» (межсезонный тег Record)
Christmas Chill и др. остаются в разделе Radio Record (genre=Radio Record),
просто скрыт сам тег-чип через hiddenTags.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-06 08:36:41 +03:00
nk
5da077b698 fix(stations): Новое Радио BY — маунт Wake Up (wakeupshow→wakeup, был 404)
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-05 21:21:52 +03:00
nk
2e970317f6 fix(stations): Record — звук на станциях с мёртвым stream_128 (Лето и др.)
У части станций Record поле stream_128 ведёт на мёртвый маунт {prefix}64.aacp
(404) — обложка/трек есть, а поток молчит (Summer Lounge, Beach Party, Reggae,
Mashup, Afro House, Nu Dance, Workout, Gop FM…). Поле stream_320 ({prefix}96.aacp)
живо у всех. Сменён приоритет выбора потока на stream_320.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-05 21:10:48 +03:00
nk
be6e1acfd8 fix(stations): жанровые чипы Record (Лето и др.) больше не пустые
Record API кладёт категории станции в поле "genre" (массив {id,name}), а
StationDto/ApiMapper читали только "tags" (у станции отсутствует) → у всех
станций Рекорда жанровые теги были пустыми, и чипы вроде «Лето» при клике
показывали пустоту. Добавлено поле genres (@SerialName genre), маплю genre+tags
в Station.tags. Раздел «Лето» теперь наполняется летними станциями Record
(Chill House, Beach Party, Tropical, Summer Lounge, Mashup и др.).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-05 20:52:21 +03:00
nk
5408bbd6c5 fix(stations): ГУСЬ — потоки на канонический https://radiogoose.ru/listen/{slug}/play
Многострочные stream_url (url1\nurl2) рвали воспроизведение и health-check.
Почищены на одиночный HTTPS-поток AzuraCast (16 каналов).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-05 20:24:23 +03:00
nk
d504218d33 chore(stations): убраны мёртвые каналы Зайцева New year/Hvilya из каталога
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-05 20:07:28 +03:00
nk
06cb6c16f1 feat(orientation): полноценная поддержка альбомной ориентации
- боковой nav-rail слева вместо нижнего бара в альбоме (SideNavRail)
- мини-плеер уезжает под контент в альбомной раскладке
- плеер эфира: двухпанельный (обложка слева, инфо/эквалайзер/контролы справа)
- плеер записи: слева управление, справа прокручиваемый список треков
- сетки станций и избранного: 4 колонки в альбоме вместо 2
- хелпер isLandscape() через LocalConfiguration

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-04 20:19:47 +03:00
nk
fabf780450 fix(now-playing): трек/обложка не обновлялись — залипшее socket-значение
Корень: NowPlayingSocketClient копит трек по станции и не чистит; combine
предпочитал socket (socketMap[id] ?: restMap[id]). Если сокет один раз
прислал трек и отвалился, залипшее значение НАВСЕГДА затеняло свежий REST —
на открытом плеере трек/обложка не менялись (Radio Record и др.). Теперь
приоритет REST (он регулярно поллится), socket — фолбэк. Поллинг плеера
ускорен 10с→5с.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-04 19:15:40 +03:00
nk
53cd1601dc fix(recordings): не зависать плееру записи; меньше задержка обложки
Bug1: плеер записи (singleton ExoPlayer) не глушился при закрытии шторки и
уходе с экрана → аудио-сирота без управления, запуск радио конфликтовал.
Теперь воспроизведение записи останавливается на onDismiss и onDispose
экрана записей, а старт радио глушит плеер записи (взаимоисключение).

Bug2: обложка/трек на открытом плеере обновлялись с задержкой при записи.
Эмиссия спектра ограничена ~45/с (было ~86/с) — меньше перегруз перерисовки;
поллинг now-playing в захвате маркеров ускорен 15с→8с (точнее тайм-коды).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-04 19:03:44 +03:00
nk
d9c83a83e9 fix(player): меньше задержка эквалайзера — окно FFT 2048→1024
Визуал отставал от бита. Главная остаточная задержка — окно FFT 2048 (Hann
даёт групповую задержку ~окно/2 ≈ 20мс) + редкие обновления. Окно 1024:
задержка реакции вдвое меньше, обновлений вдвое больше. Лайвность держит
автогейн, низов хватает (binHz ~43 покрывает бочку).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-04 18:37:25 +03:00
nk
1dfee941a0 fix(player): эквалайзер «в ритм» — перекрытие окон + быстрый спад
Визуализатор отставал/висел: медленный спад (бар держался ~300мс после
удара) и редкие обновления. Теперь FFT с перекрытием 50% (~43 обновл/с),
мгновенный рост на удар и быстрый спад (0.78→0.55), убран искусственный
троттл 33мс. Реакция плотнее попадает в бит.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-04 18:25:26 +03:00
nk
1e00287486 feat(player): 4 стиля визуализатора + выбор в настройках
Добавлены стили анимации воспроизведения: столбики от центра, столбики
снизу (спектр), плавная волна, радиальный — все от реального спектра звука
(Visualizer.kt). Пользователь выбирает стиль в Настройках → «Анимация
воспроизведения» (живые превью каждого стиля, тап выбирает). Сохраняется
пер-юзер (DataStore visualizer_style). Плеер рисует выбранный стиль
(радиальный — повыше). Превью и пауза — мягкая «дышащая» анимация.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-04 18:18:55 +03:00
nk
900a4ad813 fix(player): живой эквалайзер — автогейн + частотный маппинг
Эквалайзер почти не двигался: лог-маппинг схлопывал низы в 1-2 бина,
нормализация была слабой (двигались лишь правые полосы). Переделано:
FFT 1024→2048 (разрешение низов), полосы по частотам 40Гц-16кГц со
средним по бинам, автогейн по бегущему пику (всегда полная высота),
перцептивный лифт (sqrt) + лёгкий подъём верхов. Теперь реагируют все
полосы и заметно.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-04 18:09:40 +03:00
nk
05e5538945 feat(player): живой эквалайзер по реальному звуку (FFT-спектр)
Эквалайзер на плеере больше не декоративная синус-волна — реагирует на
реальный звук. Через TeeAudioProcessor подключаемся к декодированному PCM в
аудио-конвейере ExoPlayer (без разрешений/микрофона), считаем FFT → лог-полосы
(AudioSpectrumAnalyzer), PlayerController отдаёт спектр StateFlow'ом, LiveEqualizer
рисует столбики по уровням (с быстрым ростом/плавным спадом). Когда звука нет
(пауза/float-выход) — фолбэк на прежнюю синус-волну.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-04 17:39:09 +03:00
nk
a46e437351 feat(player): 3D-переворот обложки при смене трека
Вместо простой смены — эффект переворота (как страница альбома/пластинка):
старая обложка улетает передней гранью (0–90°), новая прилетает задней
(90–180°, контр-вращение чтобы не зеркалилась). Компонент FlipCover,
подключён к обложке в плеере; срабатывает при смене coverUrl трека.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-04 17:19:10 +03:00
nk
147b3ac81d feat(covers): приоритет играющего трека + троттл 0.8с
Обложки наливались общей очередью (1.5с) — играющий трек ждал свою очередь.
Добавлена приоритетная дорожка: трек, который слушают сейчас, обогащается
первым (PlayerViewModel → NowPlayingRepository.enrichCoverNow). Троттл общей
очереди ускорен 1.5с→0.8с. Дедуп разнесён на enqueued/processed, чтобы
дорожки не дублировали работу.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-04 17:11:44 +03:00
nk
4a33aa6fb5 feat(covers): клиентское обогащение обложек через iTunes (обход бана сервера)
Серверный IP забанен Apple (iTunes search 429), а Deezer из РФ пуст — обложки
перестали наливаться. Теперь iTunes-поиск делает КЛИЕНТ (его IP не забанен):
для now-playing-треков без обложки ищет арт в iTunes и шлёт ССЫЛКУ на наш
бэкенд (POST /covers/submit), сервер качает её (CDN из РФ доступен) и кладёт
WebP — дальше обложка приходит всем через /now-playing. Дедуп по треку +
троттлинг 1.5с (CoverEnrichmentManager). Сервер: host-whitelist (SSRF),
идемпотентность (first-write-wins).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-04 16:59:32 +03:00
nk
4612a8f33c fix(player): следовать кросс-протокольным редиректам (http→https)
Многие станции отдают по http 301 на https; ExoPlayer по умолчанию не идёт
по кросс-протокольному редиректу и не играет их. Включён общий HTTP-источник
с setAllowCrossProtocolRedirects(true) — такие станции заиграют без правки URL.
ICY-метаданные сохраняются (обрабатываются на уровне ProgressiveMediaSource).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-04 15:42:43 +03:00
nk
bd62016026 fix(stations): Royal Radio — https вместо http (ничего не играло)
royalradio.space по http отдаёт 301 на https, а ExoPlayer по умолчанию НЕ
следует кросс-протокольным редиректам (http→https) — поэтому все 10 каналов
Royal Radio не воспроизводились. Потоки переведены на прямой https (200
audio/mpeg). Прод-БД тоже обновлена (для ICY now-playing).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-04 15:31:09 +03:00
nk
b2aff51c62 feat(stations): оживить главный «Радио Романтика» в разделе Romantika
В разделе Romantika были только саб-каналы (Piano Covers, Love Songs,
Акустика, Прикосновение, Easy Listening), а главный «Romantika» (711) был
отключён — мёртвый поток srv21.gpmradio (и в offline-ids бэкенда). Включил
главный на рабочем HLS (hls-01-gpm.hostingradio.ru/romantika495) + фирменный
логотип Романтики (применяется ко всем каналам сети). Прод-БД: 711 → online.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-04 15:18:21 +03:00
nk
4a9622ca92 feat(stations): добавить Like FM (главный канал) в раздел Like FM
Раздел Like FM был пустой — все тематические каналы «Хиты по годам» (101.ru)
закрыты (404). Like FM теперь вещает как единый канал (на сайте — только
региональные FM-частоты того же эфира). Включил главный Like FM на рабочем
HLS (hls-01-gpm.hostingradio.ru/likefm495, Москва 87.9), группа «Like FM»,
+ фирменный логотип. Бэкенд: 718 помечена online (была в offline-ids).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-04 15:05:04 +03:00
nk
8d2c53c441 feat(stations): скрывать украинские станции (ROKS, Kiss FM) для РФ
Radio ROKS и Kiss FM (TavR Media, хосты radioroks.ua / kissfm.ua) недоступны
с российских IP без VPN. Теперь для пользователей из РФ они полностью скрыты
— и сами станции (везде, где используется список), и их чипы-категории.

Страна определяется по IP (api.country.is → ipapi.co; при VPN вернёт страну
выходного узла, тогда станции доступны и НЕ скрываются), с фолбэком на страну
SIM/сети/локали устройства, если IP-сервис недоступен (в РФ часто заблокирован).
Код страны кэшируется (DataStore). Фильтр в GetStationsUseCase (combine со
страной) + чипы в StationsViewModel. id 741 «Радио РОКС» (stream.roks.com) —
российская, под правило не попадает.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-04 14:46:42 +03:00
nk
4697e27eb4 fix(stations): свечение верхнего ряда не обрезается, уходит под чипы
Грид растянут под чипы (верхний contentPadding = высота чипов), а чипы
вынесены отдельным слоем поверх грида с фоном-градиентом (вверху
непрозрачный — маскирует прокрутку, книзу прозрачный). Свечение играющей
станции из верхнего ряда больше не режется границей и мягко проступает
из-под чипов категорий.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-04 14:27:41 +03:00
nk
b6c0e92758 fix(stations): бесшовная петля свечения играющей станции
Центр свечения по cy двигался с sin(t*1.3) — некратная гармоника давала
скачок на стыке цикла. Заменено на sin(2t): значения и скорость совпадают
на t=0 и t=2π, петля повторяется ровно и плавно.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-04 14:14:46 +03:00
nk
9268e14cc6 feat(stations): свайп по списку листает чипы + свечение играющей станции
1) Горизонтальный свайп по области списка переключает фильтры-чипы в их
   порядке ([Все]+жанры), выбранный чип автоскроллится в зону видимости.
   Вертикальная прокрутка грида сохраняется.

2) У играющей станции в списке — мягкое радиальное свечение позади обложки,
   которое «гуляет» (двигается центр) и вылезает из-под краёв, + эквалайзер-
   бейдж в углу. Источник активной станции — PlayerController.currentStationId.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-04 14:12:01 +03:00
nk
603e232dff fix(recordings): шторка записи на весь экран, список треков над навигацией
navigationBarsPadding не применялся в partial-режиме ModalBottomSheet —
список треков налезал на системную навигацию. Включён skipPartiallyExpanded
(как у радио-плеера) + navigationBarsPadding на контенте.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-04 13:49:08 +03:00
nk
b3912a9dca fix(recordings): список треков не уходит под системную навигацию
У RecordingPlayerSheet не было navigationBarsPadding — нижние строки
списка треков накладывались на кнопки навигации Android. Добавлен отступ
под навбар (вне скролла, чтобы низ всегда был над кнопками).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-04 13:44:15 +03:00
nk
7df9b62403 feat(recordings): запись HLS-станций (EMG: Европа Плюс и др.)
Раньше запись просто писала тело URL в файл — у HLS это m3u8-плейлист
(текст), а не аудио, поэтому EMG-станции не записывались. Добавлен
HLS-рекордер: резолвит мастер→медиа-плейлист, опрашивает его и докачивает
новые .ts-сегменты, склеивая в файл (валидный MPEG-TS, ExoPlayer играет
и перематывает). На первом проходе пишется только хвост окна — запись
начинается примерно с момента нажатия. Сплошные потоки (ICY) — прежним
путём (recordRaw). Тайм-коды треков работают и для EMG (now-playing с бэка).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-04 13:39:27 +03:00
nk
fc63814f97 feat(recordings): перемотка записей + тайм-коды треков
1) Перемотка: записи эфира — сырой ADTS-AAC/MP3 без индексов, ExoPlayer
   считал их неперематываемыми (старт всегда с нуля). Включён CBR-seeking
   (DefaultExtractorsFactory.setConstantBitrateSeekingEnabled) — seek работает.

2) Тайм-коды треков: при записи фиксируются смены now-playing с offset от
   начала (модель TrackMarker, колонка markers в recordings, миграция v6,
   захват через NowPlayingRepository — свой поллинг, не зависит от экрана).
   В плеере записи — список «Треки в записи»: тайм-код + название, тап
   переходит к моменту, текущий трек подсвечен.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-04 13:18:23 +03:00
nk
777f5d5082 fix(favorites): не терять избранное после перезапуска приложения
refreshStations пересоздавал каталог с isFavorite=false, а insertAll
(OnConflictStrategy.REPLACE) затирал строки — отметки «избранное»
пропадали при каждом старте. Перед вставкой считываем текущие id
избранного (getFavoriteIdsOnce) и проставляем их новым записям.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-04 12:53:55 +03:00
nk
6aa2588641 fix(player): не обрезать низ плеера на телефонах (скролл + компактнее)
Плеер живёт в ModalBottomSheet без скролла. На телефонах с высоким dpi
высоты в dp меньше (480dpi → ~800dp против ~914dp у эмулятора 420dpi),
из-за чего низ — кнопка «Текст песни» — обрезался шторкой и был виден
лишь полоской. Добавлен verticalScroll (низ доступен на любом экране) и
ужата высота (обложка 220→190, крупные отступы), чтобы влезало без скролла.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-04 12:51:15 +03:00
nk
c77c131a09 fix(player): крупная видимая кнопка «Текст песни» (пилюля с фоном)
На реальном телефоне мелкий TextButton (13sp + иконка 16dp в приглушённом
акценте) почти не виден. Заменён на пилюлю с фоном surface2: иконка 20dp,
текст 15sp medium — читается на физическом экране.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-04 12:44:44 +03:00
nk
5ffaf9a924 feat(player): переключатель качества звука на экране воспроизведения
Перепроверены все 594 рабочие станции на наличие битрейт-вариантов
потока (скрипт-пробер). У 71 станции найдено по 2–4 качества
(Record-флагманы 96/64/32, zaycev 256/128/48, ВГТРК 192/128/64,
НАШЕ/Орфей/Шансон HQ и др.) — записаны в поле qualities в stations.json.
HLS (EMG) и Love (UID-привязка) корректно пропущены.

Клиент: модель StreamQuality, хранение в Room (миграция v5),
предпочтение битрейта в настройках. На экране плеера — чип текущего
качества (виден только если вариантов ≥2) и шторка «Качество звука»
со ступенями; переключение на лету без сброса now-playing, выбор
запоминается между станциями.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-04 12:36:47 +03:00
nk
5b256a3421 feat(love): логотипы каналов Love Radio (меньше, с отступами) как обложки
Сгенерены из их SVG на фирменном цвете канала, захостены у нас (/covers/love_*_s.webp),
заданы через StationLogos.byName. Вместо унылых буквенных плиток — фирменные логотипы.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-03 20:33:39 +03:00
nk
320cac546b feat(love): воспроизведение Love Radio через сессионный UID + now-playing главного
Потоки Love защищены: клиент берёт UID из их player/config (со своего IP) и
подставляет в n340-поток — играет музыка. LoveStreamResolver + LoveApi. Каталог
переведён на n340. Now-playing главного Love Radio по ICY; саб-каналы трек не
отдают нигде — показываем без трека.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-03 20:14:52 +03:00
nk
615e3435e3 feat(stations): клиент скрывает оффлайн-станции с бэкенда (системно)
При обновлении каталога тянем GET /stations/offline-ids и удаляем эти станции
из локальной БД. Мёртвые плитки теперь пропадают сами (бэк их метит health-check'ом),
без пересборки приложения. Фолбэк на статичный enabled, если бэк недоступен.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-03 18:04:35 +03:00
nk
4c4c6e05d8 chore(stations): отключить 67 мёртвых станций (потоки не отвечают)
Свип по всем потокам (корректная проверка: живой = пришли заголовки 200,
мёртвый = ошибка/4xx/5xx/нет ответа). Помечены enabled=false. Активных 595/697.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-03 17:48:30 +03:00
nk
4a45cb575e chore(stations): отключить мёртвые каналы Европы Плюс (Acoustic, ResiDance)
Потоки не отвечают (000/404), meta now-playing пуст — каналы не вещают.
enabled=false → скрыты в приложении.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-03 17:05:00 +03:00
nk
1ef60b6053 fix(now-playing): матч текущего трека по id станции, а не по имени
Станции с одинаковым именем в разных сетях (напр. «Deep» у Record и DFM)
показывали один и тот же трек — матч был по lowercase-имени. Каталожный id
(== station.id) уникален и совпадает со stationId в /now-playing, поэтому
матчим по id. Убран весь by-name путь (репозиторий, плеер, карточки).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-03 15:54:24 +03:00
nk
eeceb754ea feat(stations): актуальные emgsound HLS-потоки линейки Европы Плюс
8 каналов EP (Europa Plus/Top 40/New/Party/Urban/Acoustic/ResiDance/Fresh)
переведены на рабочие emgsound HLS — играют + получают now-playing/обложки.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-03 15:47:45 +03:00
nk
b93bec028e feat(player): показывать название станции под «В ЭФИРЕ» над обложкой
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-03 14:55:48 +03:00
nk
72ecbae866 fix(player): матч now-playing по имени станции (обложки DFM в плеере)
Плеер искал now-playing по числовому id станции, а у локальных станций (DFM)
id не совпадает с каталожным → API-путь с обложкой не срабатывал, плеер падал
на ICY из потока (без обложки). Теперь getNowPlaying матчит по id, затем по
имени станции (как карточки). DFM-обложки появляются и в плеере.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-03 14:36:39 +03:00
nk
77772789bb fix(ui): подпись играющего трека на карточке станции даже без обложки трека
Раньше now-track (трек/исполнитель + обложка) показывался ТОЛЬКО при наличии
обложки трека — поэтому DFM-станции без обогащённой обложки оставались пустой
плиткой. Теперь: если трек известен — всегда показываем подпись, а фоном берём
обложку трека → лого станции → плитку. DFM работает как Record.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-03 14:16:41 +03:00
nk
99503fc77a feat(charts): фильтр по жанру + жанр/стиль/лейбл/год на детальной трека
Подтягиваем обогащённые данные с бэкенда (Discogs): genre/styles/label/year
в чартах и детальной странице.

- ChartEntry/TrackStats + DTO: добавлены genre/styles/label/year
- RadiolaApi: getCharts(?genre=), новый getGenres()
- ChartsViewModel: состояние выбранного жанра + список жанров, перезагрузка
- ChartsScreen: ряд чипов-фильтров по жанру (Все + жанры),
  жанр/стили чипами и «Лейбл · Год» на детальной
- убран демо-fallback (SAMPLE_CHARTS) — бэкенд живой

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
2026-06-03 13:55:35 +03:00
nk
b0c3dae20a feat(stations): локальные обложки Comedy FM/Spa/StandUp/Женский StandUp
вшиты в ресурсы (res/drawable), привязаны по имени станции (приоритет над
логотипом по домену). Загрузка через android.resource:// в Coil.
2026-06-03 12:35:03 +03:00
nk
5e22db5571 feat(stations): кураторские логотипы по домену сайта (Comedy Radio)
StationLogos: карта домен -> URL логотипа для сетей без своего API обложек.
Comedy Radio (Comedy FM/Club/Spa, comedy-radio.ru) -> официальный apple-touch
логотип. Расширяемо по сетям.
2026-06-03 12:26:11 +03:00
nk
ee689ce380 feat(stations): обложка текущего трека на карточке станции + подпись
Для станций без своей обложки (и для Radio Record — единый стиль) карточка
показывает обложку играющего трека с тёмным градиентом и подписью трек/исполнитель.
Источник — /now-playing (теперь с name станции), матч по имени, обновление 20с.
Приоритет: трек -> логотип станции -> фирменная плитка.
2026-06-03 12:18:19 +03:00
nk
9d115b148e fix(lyrics): краш при открытии текста — Unspecified lineHeight
bodyLarge.lineHeight не задан (Unspecified), умножение на 1.4f бросало
IllegalArgumentException (Cannot perform operation for Unspecified type).
Задан конкретный lineHeight = 22.sp.
2026-06-03 11:55:31 +03:00
nk
ba32973beb feat(lyrics): тексты песен внутри приложения через LRCLIB
- LrcLibApi (api/get + api/search, User-Agent), DI @Named(lrclib) Retrofit
- LyricsRepository.fetchLyrics -> LyricsResult (plain/synced/instrumental)
- LyricsViewModel + LyricsSheet (загрузка/инструментал/найдено/не найдено),
  прокрутка + атрибуция LRCLIB
- кнопка «Текст песни» открывает встроенный экран (плеер + деталь трека чартов),
  вместо ссылки в браузере
2026-06-03 11:47:00 +03:00
nk
5fd97d27fd fix(stations): обложки Record только для Record-станций + своя плитка остальным
- сети, отличные от Radio Record (DFM, HitFM и др.), больше не получают
  обложки Radio Record (обогащение Record API гейтится по source=record)
- станции без обложки рисуют свою фирменную плитку: цвет по названию + инициалы
  (вместо общего значка/чужой обложки)
2026-06-03 11:36:24 +03:00
nk
32e5108d98 fix(stations): подтягивать обложки/потоки Record по названию станции
Локальные станции (assets/stations.json, id 1,2,3...) обогащались данными
Record только по id, но id Record-каталога другие (15016...) и prefix в
ассетах нет — поэтому совпадений почти не было и обложки не грузились.
Добавлен фолбэк-матч по названию станции (стабильный общий ключ).
2026-06-03 11:22:57 +03:00
nk
a50a108f63 fix(ui): иконочный таб-бар, заголовок станций, ровные кнопки плеера, рабочая ссылка на текст
- таб-бар только иконки (6 разделов не помещались с подписями)
- «Откройте радио» -> «Выберите радиостанцию»
- кнопки плеера (лайк/prev/next/запись) единого размера 24/48, ряд SpaceBetween
  (кнопка записи больше не обрезается и не выбивается размером)
- текст песни: Musixmatch резал соединение -> веб-поиск трека (открывается)
2026-06-03 11:15:29 +03:00
nk
fc9b23f62c fix(player): now-playing с нашего бэкенда вместо сырого Record-эндпоинта
Record /stations/now использует id now-слотов, не совпадающие с id каталога,
поэтому клиент не находил трек по station.id (трек/обложка не показывались).
Теперь берём GET /now-playing с нашего бэка (корректный маппинг recordSync,
ключ = id станции) -> плеер показывает название трека и обложку.
2026-06-03 10:59:59 +03:00
nk
eca0c49ad4 fix(ui): тёмный сплэш с фирменной иконкой вместо белого экрана
- Theme.Radiola -> тёмная (windowBackground #0C1410), прозрачные системные бары
- Theme.Radiola.Splash (core-splashscreen): фон #0C1410 + иконка приложения
- installSplashScreen() в MainActivity; тема сплэша на launcher-активити
2026-06-03 00:27:29 +03:00
nk
e190444577 feat: фирменная иконка приложения + внутренний плеер записей
- адаптивная иконка лаунчера: градиентный фон (C2F25B->6FA53C) + монограмма R
  (foreground + monochrome для тем Android 13), манифест -> @mipmap
- воспроизведение своих записей ВНУТРИ приложения вместо внешнего плеера:
  RecordingPlaybackController (отдельный ExoPlayer, останавливает радио),
  RecordingPlayerSheet с перемоткой (Slider), play/pause, +/-15с, таймеры
2026-06-03 00:13:12 +03:00
nk
d0e5f4e8c5 feat(charts): раздел «Чарты» (клиент) + детальная страница трека с графиком
- вкладка «Чарты» в навигации; экран: периоды (День/Неделя/Месяц/Всё),
  ранжированный список треков (ранг, обложка, проигрывания, тренд)
- детальная карточка трека: метрики, график популярности (Canvas), лайк,
  кнопки музыкальных сервисов, кнопка «Текст песни» (ссылка на лицензированный
  Musixmatch — полный текст не встраиваем, авторское право)
- ChartsRepository/LyricsRepository + эндпоинты charts/* в RadiolaApi (DTO)
- превью-данные пока бэкенд не отдаёт charts (помечено TODO)
2026-06-02 23:24:42 +03:00
nk
a4af72a6e6 polish(ui): плавные обложки, бегущая строка длинных названий, тактильный отклик
- Coil crossfade для всех обложек (Images.crossfadeModel) — без «моргания» при загрузке
- basicMarquee для длинных названий трека (плеер и мини-плеер) вместо обрезки
- haptic feedback на play/pause и добавление в избранное (плеер, мини-плеер, карточка)
2026-06-02 22:55:18 +03:00
nk
310d6c3177 fix(player): отображение трека и обложки — объединение REST и socket now-playing
REST-поллинг (refreshNowPlaying -> api.getNowPlaying, 200 OK) писал данные в
_nowPlaying, который нигде не читался; getNowPlaying() брал только сокет (пустой).
Теперь getNowPlaying/getAllNowPlaying объединяют оба источника (socket ?: REST),
поэтому название трека, обложка и deep-link сервисов работают.
2026-06-02 22:55:18 +03:00
nk
cefd0be009 fix(ui): отступы под системную навигацию + подписи сервисов + краш навбара
- навбар и мини-плеер: navigationBarsPadding — не налезают на системные кнопки
- плеер: navigationBarsPadding снизу, ряд сервисов не уходит под системную панель
- подписи сервисов без обрезки слов (Яндекс / ВК Музыка / YT Music и т.д.)
- фикс NPE при холодном старте: навбар обращается к NavDestinations напрямую,
  не к companion-списку (порядок инициализации Kotlin)
2026-06-02 22:55:17 +03:00
nk
af13272852 fix(ui): единый скролл на экране станций + всегда видимый навбар
- StationsScreen: закреплённые заголовок/поиск/жанры, одна прокручиваемая
  сетка станций; поиск и фильтры больше не исчезают при пустом результате
  (+ кнопка «Сбросить фильтры»)
- таб-бар показывается без обязательного входа (скрыт только на экране входа)
- старт сразу со «Станций» — авторизация необязательна, вход из Настроек
2026-06-02 22:55:17 +03:00
nk
220d1d6fa1 feat(ui): мягкие переходы между экранами (fade + лёгкий slide) 2026-06-02 22:55:17 +03:00
nk
f604ad42e8 feat(ui): рестайл всех экранов + плеер + официальные mono-логотипы сервисов
- экраны (Станции/Избранное/История/Записи/Настройки/Вход): двухцветные
  заголовки, токены темы, EmptyState, анимации появления и перестановки
- AuthScreen: брендовый локап (AppMark + RadiolaWordmark)
- PlayerBottomSheet: живой эфир — LiveEqualizer вместо перемотки,
  Crossfade трека и play/pause, pressScale, анимация избранного/записи
- кнопки музыкальных сервисов: монохромные официальные логотипы
  (vector drawable из Simple Icons CC0 + Yandex), маппинг serviceLogoRes
- DeeplinkBottomSheet: сетка сервисов с логотипами
2026-06-02 22:55:17 +03:00
nk
d652dc399a feat(ui): рестайл общих компонентов под дизайн-систему
- StationCard: обложка/иконка-заглушка, анимированное сердечко, pressScale
- MiniPlayer: elevated-бар, метка «СЕЙЧАС ИГРАЕТ», Crossfade play/pause
- SearchBar: surface-поле, акцентный курсор, скругление 14
- FilterChips: акцентный активный чип с анимацией цвета
- EmptyState: иконка-плашка + текст
- TrackListItem: thumb-заглушка, pressScale
2026-06-02 22:55:17 +03:00
nk
ae406554de feat(ui): дизайн-система radiOLA — палитра, тема, типографика, бренд, motion, pill таб-бар
- цветовые токены тёмно-зелёной темы + RadiolaColors (CompositionLocal)
- darkColorScheme + всегда тёмная тема, фирменные shapes
- типографика с весами/размерами под макет
- Brand: AppMark (градиентный R), RadiolaWordmark, MonoMark
- Motion: спеки движения, pressScale, живой эквалайзер
- pill-таб-бар с анимированной активной вкладкой
2026-06-02 22:55:17 +03:00
nk
2f686bcc57 chore: add .gitignore and remove build artifacts from index 2026-06-02 22:50:00 +03:00
nk
bcb999ace9 feat: WebSocket now-playing via Socket.IO from backend 2026-06-02 19:52:15 +03:00
nk
a83672b455 feat: auth screen with auto-redirect, sync favorites/history with backend 2026-06-02 19:12:07 +03:00
nk
d4adb1e7be fix: add launcher icons and update manifest references 2026-06-01 13:35:28 +03:00
nk
bc94577276 chore: add Gradle wrapper 8.7 2026-06-01 13:26:38 +03:00
nk
59f62a22b2 test: add unit tests for use cases and ViewModel, add Compose UI test 2026-06-01 13:23:11 +03:00
nk
af8fb333d9 feat(widget): add 4x1 AppWidgetProvider with play/pause and track info 2026-06-01 13:21:37 +03:00
nk
9ce9758361 feat(player): wire StationsScreen and FavoritesScreen to actual playback 2026-06-01 13:19:23 +03:00
nk
ada422053f feat(deeplink): add DeeplinkNavigator, DeeplinkBottomSheet and integrate into History and Player 2026-06-01 13:15:31 +03:00
nk
aa287f7588 feat(ui): integrate MiniPlayer into Scaffold with real player state 2026-06-01 13:12:51 +03:00
nk
9e3ce0f1e4 feat(ui): wire all screens into NavHost with BottomSheet player 2026-06-01 13:07:11 +03:00
nk
15e15c6664 feat(ui): add SettingsScreen and SettingsViewModel 2026-06-01 13:06:08 +03:00
nk
d3cec3bba2 feat(ui): add HistoryScreen and HistoryViewModel 2026-06-01 13:04:35 +03:00
nk
b2af81c070 feat(ui): add FavoritesScreen and FavoritesViewModel 2026-06-01 13:03:24 +03:00
nk
ee91837910 feat(ui): add PlayerBottomSheet and PlayerViewModel 2026-06-01 13:02:16 +03:00
nk
1c902b5607 feat(ui): add StationsScreen and StationsViewModel 2026-06-01 13:00:12 +03:00
nk
116ab95abd feat(ui): add shared components (StationCard, TrackListItem, SearchBar, FilterChips, MiniPlayer, EmptyState) 2026-06-01 12:58:25 +03:00
nk
28309c201e chore: add Lucide icons dependency and replace Material Icons in navigation 2026-06-01 12:54:36 +03:00
nk
c46a865742 feat(ui): add bottom navigation with 4 tabs 2026-06-01 12:23:27 +03:00
nk
cf79af5273 feat(service): add ExoPlayer controller and MediaSessionService 2026-06-01 12:21:22 +03:00
nk
9d68459df6 feat(di): add Hilt AppModule with Retrofit, Room and repository bindings 2026-06-01 12:19:33 +03:00
nk
e255b0458d feat(data): add repository implementations 2026-06-01 12:18:10 +03:00
nk
110fe0795e feat(data): add Room entities, DAOs and AppDatabase 2026-06-01 12:12:55 +03:00
nk
62674fcc3f feat(data): add Retrofit API, DTOs and mappers 2026-06-01 12:11:15 +03:00
nk
828cdf9a50 feat(domain): add core use cases 2026-06-01 12:08:49 +03:00
nk
aad1361043 feat(domain): add repository interfaces 2026-06-01 12:07:29 +03:00
nk
d345cd40b8 feat(domain): add Station, Track, PlayerState, DeeplinkService models 2026-06-01 12:05:13 +03:00
nk
7b1aa0c073 feat: add Application, MainActivity and Material3 theme 2026-06-01 12:02:35 +03:00
nk
8f26bf16d3 chore: add app module build config and manifest 2026-06-01 11:57:59 +03:00
nk
082e895f6a chore: bootstrap root Gradle with version catalog 2026-06-01 11:54:39 +03:00
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# React Composition Patterns
**Version 1.0.0**
Engineering
January 2026
> **Note:**
> This document is mainly for agents and LLMs to follow when maintaining,
> generating, or refactoring React codebases using composition. Humans
> may also find it useful, but guidance here is optimized for automation
> and consistency by AI-assisted workflows.
---
## Abstract
Composition patterns for building flexible, maintainable React components. Avoid boolean prop proliferation by using compound components, lifting state, and composing internals. These patterns make codebases easier for both humans and AI agents to work with as they scale.
---
## Table of Contents
1. [Component Architecture](#1-component-architecture) — **HIGH**
- 1.1 [Avoid Boolean Prop Proliferation](#11-avoid-boolean-prop-proliferation)
- 1.2 [Use Compound Components](#12-use-compound-components)
2. [State Management](#2-state-management) — **MEDIUM**
- 2.1 [Decouple State Management from UI](#21-decouple-state-management-from-ui)
- 2.2 [Define Generic Context Interfaces for Dependency Injection](#22-define-generic-context-interfaces-for-dependency-injection)
- 2.3 [Lift State into Provider Components](#23-lift-state-into-provider-components)
3. [Implementation Patterns](#3-implementation-patterns) — **MEDIUM**
- 3.1 [Create Explicit Component Variants](#31-create-explicit-component-variants)
- 3.2 [Prefer Composing Children Over Render Props](#32-prefer-composing-children-over-render-props)
4. [React 19 APIs](#4-react-19-apis) — **MEDIUM**
- 4.1 [React 19 API Changes](#41-react-19-api-changes)
---
## 1. Component Architecture
**Impact: HIGH**
Fundamental patterns for structuring components to avoid prop
proliferation and enable flexible composition.
### 1.1 Avoid Boolean Prop Proliferation
**Impact: CRITICAL (prevents unmaintainable component variants)**
Don't add boolean props like `isThread`, `isEditing`, `isDMThread` to customize
component behavior. Each boolean doubles possible states and creates
unmaintainable conditional logic. Use composition instead.
**Incorrect: boolean props create exponential complexity**
```tsx
function Composer({
onSubmit,
isThread,
channelId,
isDMThread,
dmId,
isEditing,
isForwarding,
}: Props) {
return (
<form>
<Header />
<Input />
{isDMThread ? (
<AlsoSendToDMField id={dmId} />
) : isThread ? (
<AlsoSendToChannelField id={channelId} />
) : null}
{isEditing ? (
<EditActions />
) : isForwarding ? (
<ForwardActions />
) : (
<DefaultActions />
)}
<Footer onSubmit={onSubmit} />
</form>
)
}
```
**Correct: composition eliminates conditionals**
```tsx
// Channel composer
function ChannelComposer() {
return (
<Composer.Frame>
<Composer.Header />
<Composer.Input />
<Composer.Footer>
<Composer.Attachments />
<Composer.Formatting />
<Composer.Emojis />
<Composer.Submit />
</Composer.Footer>
</Composer.Frame>
)
}
// Thread composer - adds "also send to channel" field
function ThreadComposer({ channelId }: { channelId: string }) {
return (
<Composer.Frame>
<Composer.Header />
<Composer.Input />
<AlsoSendToChannelField id={channelId} />
<Composer.Footer>
<Composer.Formatting />
<Composer.Emojis />
<Composer.Submit />
</Composer.Footer>
</Composer.Frame>
)
}
// Edit composer - different footer actions
function EditComposer() {
return (
<Composer.Frame>
<Composer.Input />
<Composer.Footer>
<Composer.Formatting />
<Composer.Emojis />
<Composer.CancelEdit />
<Composer.SaveEdit />
</Composer.Footer>
</Composer.Frame>
)
}
```
Each variant is explicit about what it renders. We can share internals without
sharing a single monolithic parent.
### 1.2 Use Compound Components
**Impact: HIGH (enables flexible composition without prop drilling)**
Structure complex components as compound components with a shared context. Each
subcomponent accesses shared state via context, not props. Consumers compose the
pieces they need.
**Incorrect: monolithic component with render props**
```tsx
function Composer({
renderHeader,
renderFooter,
renderActions,
showAttachments,
showFormatting,
showEmojis,
}: Props) {
return (
<form>
{renderHeader?.()}
<Input />
{showAttachments && <Attachments />}
{renderFooter ? (
renderFooter()
) : (
<Footer>
{showFormatting && <Formatting />}
{showEmojis && <Emojis />}
{renderActions?.()}
</Footer>
)}
</form>
)
}
```
**Correct: compound components with shared context**
```tsx
const ComposerContext = createContext<ComposerContextValue | null>(null)
function ComposerProvider({ children, state, actions, meta }: ProviderProps) {
return (
<ComposerContext value={{ state, actions, meta }}>
{children}
</ComposerContext>
)
}
function ComposerFrame({ children }: { children: React.ReactNode }) {
return <form>{children}</form>
}
function ComposerInput() {
const {
state,
actions: { update },
meta: { inputRef },
} = use(ComposerContext)
return (
<TextInput
ref={inputRef}
value={state.input}
onChangeText={(text) => update((s) => ({ ...s, input: text }))}
/>
)
}
function ComposerSubmit() {
const {
actions: { submit },
} = use(ComposerContext)
return <Button onPress={submit}>Send</Button>
}
// Export as compound component
const Composer = {
Provider: ComposerProvider,
Frame: ComposerFrame,
Input: ComposerInput,
Submit: ComposerSubmit,
Header: ComposerHeader,
Footer: ComposerFooter,
Attachments: ComposerAttachments,
Formatting: ComposerFormatting,
Emojis: ComposerEmojis,
}
```
**Usage:**
```tsx
<Composer.Provider state={state} actions={actions} meta={meta}>
<Composer.Frame>
<Composer.Header />
<Composer.Input />
<Composer.Footer>
<Composer.Formatting />
<Composer.Submit />
</Composer.Footer>
</Composer.Frame>
</Composer.Provider>
```
Consumers explicitly compose exactly what they need. No hidden conditionals. And the state, actions and meta are dependency-injected by a parent provider, allowing multiple usages of the same component structure.
---
## 2. State Management
**Impact: MEDIUM**
Patterns for lifting state and managing shared context across
composed components.
### 2.1 Decouple State Management from UI
**Impact: MEDIUM (enables swapping state implementations without changing UI)**
The provider component should be the only place that knows how state is managed.
UI components consume the context interface—they don't know if state comes from
useState, Zustand, or a server sync.
**Incorrect: UI coupled to state implementation**
```tsx
function ChannelComposer({ channelId }: { channelId: string }) {
// UI component knows about global state implementation
const state = useGlobalChannelState(channelId)
const { submit, updateInput } = useChannelSync(channelId)
return (
<Composer.Frame>
<Composer.Input
value={state.input}
onChange={(text) => sync.updateInput(text)}
/>
<Composer.Submit onPress={() => sync.submit()} />
</Composer.Frame>
)
}
```
**Correct: state management isolated in provider**
```tsx
// Provider handles all state management details
function ChannelProvider({
channelId,
children,
}: {
channelId: string
children: React.ReactNode
}) {
const { state, update, submit } = useGlobalChannel(channelId)
const inputRef = useRef(null)
return (
<Composer.Provider
state={state}
actions={{ update, submit }}
meta={{ inputRef }}
>
{children}
</Composer.Provider>
)
}
// UI component only knows about the context interface
function ChannelComposer() {
return (
<Composer.Frame>
<Composer.Header />
<Composer.Input />
<Composer.Footer>
<Composer.Submit />
</Composer.Footer>
</Composer.Frame>
)
}
// Usage
function Channel({ channelId }: { channelId: string }) {
return (
<ChannelProvider channelId={channelId}>
<ChannelComposer />
</ChannelProvider>
)
}
```
**Different providers, same UI:**
```tsx
// Local state for ephemeral forms
function ForwardMessageProvider({ children }) {
const [state, setState] = useState(initialState)
const forwardMessage = useForwardMessage()
return (
<Composer.Provider
state={state}
actions={{ update: setState, submit: forwardMessage }}
>
{children}
</Composer.Provider>
)
}
// Global synced state for channels
function ChannelProvider({ channelId, children }) {
const { state, update, submit } = useGlobalChannel(channelId)
return (
<Composer.Provider state={state} actions={{ update, submit }}>
{children}
</Composer.Provider>
)
}
```
The same `Composer.Input` component works with both providers because it only
depends on the context interface, not the implementation.
### 2.2 Define Generic Context Interfaces for Dependency Injection
**Impact: HIGH (enables dependency-injectable state across use-cases)**
Define a **generic interface** for your component context with three parts:
`state`, `actions`, and `meta`. This interface is a contract that any provider
can implement—enabling the same UI components to work with completely different
state implementations.
**Core principle:** Lift state, compose internals, make state
dependency-injectable.
**Incorrect: UI coupled to specific state implementation**
```tsx
function ComposerInput() {
// Tightly coupled to a specific hook
const { input, setInput } = useChannelComposerState()
return <TextInput value={input} onChangeText={setInput} />
}
```
**Correct: generic interface enables dependency injection**
```tsx
// Define a GENERIC interface that any provider can implement
interface ComposerState {
input: string
attachments: Attachment[]
isSubmitting: boolean
}
interface ComposerActions {
update: (updater: (state: ComposerState) => ComposerState) => void
submit: () => void
}
interface ComposerMeta {
inputRef: React.RefObject<TextInput>
}
interface ComposerContextValue {
state: ComposerState
actions: ComposerActions
meta: ComposerMeta
}
const ComposerContext = createContext<ComposerContextValue | null>(null)
```
**UI components consume the interface, not the implementation:**
```tsx
function ComposerInput() {
const {
state,
actions: { update },
meta,
} = use(ComposerContext)
// This component works with ANY provider that implements the interface
return (
<TextInput
ref={meta.inputRef}
value={state.input}
onChangeText={(text) => update((s) => ({ ...s, input: text }))}
/>
)
}
```
**Different providers implement the same interface:**
```tsx
// Provider A: Local state for ephemeral forms
function ForwardMessageProvider({ children }: { children: React.ReactNode }) {
const [state, setState] = useState(initialState)
const inputRef = useRef(null)
const submit = useForwardMessage()
return (
<ComposerContext
value={{
state,
actions: { update: setState, submit },
meta: { inputRef },
}}
>
{children}
</ComposerContext>
)
}
// Provider B: Global synced state for channels
function ChannelProvider({ channelId, children }: Props) {
const { state, update, submit } = useGlobalChannel(channelId)
const inputRef = useRef(null)
return (
<ComposerContext
value={{
state,
actions: { update, submit },
meta: { inputRef },
}}
>
{children}
</ComposerContext>
)
}
```
**The same composed UI works with both:**
```tsx
// Works with ForwardMessageProvider (local state)
<ForwardMessageProvider>
<Composer.Frame>
<Composer.Input />
<Composer.Submit />
</Composer.Frame>
</ForwardMessageProvider>
// Works with ChannelProvider (global synced state)
<ChannelProvider channelId="abc">
<Composer.Frame>
<Composer.Input />
<Composer.Submit />
</Composer.Frame>
</ChannelProvider>
```
**Custom UI outside the component can access state and actions:**
```tsx
function ForwardMessageDialog() {
return (
<ForwardMessageProvider>
<Dialog>
{/* The composer UI */}
<Composer.Frame>
<Composer.Input placeholder="Add a message, if you'd like." />
<Composer.Footer>
<Composer.Formatting />
<Composer.Emojis />
</Composer.Footer>
</Composer.Frame>
{/* Custom UI OUTSIDE the composer, but INSIDE the provider */}
<MessagePreview />
{/* Actions at the bottom of the dialog */}
<DialogActions>
<CancelButton />
<ForwardButton />
</DialogActions>
</Dialog>
</ForwardMessageProvider>
)
}
// This button lives OUTSIDE Composer.Frame but can still submit based on its context!
function ForwardButton() {
const {
actions: { submit },
} = use(ComposerContext)
return <Button onPress={submit}>Forward</Button>
}
// This preview lives OUTSIDE Composer.Frame but can read composer's state!
function MessagePreview() {
const { state } = use(ComposerContext)
return <Preview message={state.input} attachments={state.attachments} />
}
```
The provider boundary is what matters—not the visual nesting. Components that
need shared state don't have to be inside the `Composer.Frame`. They just need
to be within the provider.
The `ForwardButton` and `MessagePreview` are not visually inside the composer
box, but they can still access its state and actions. This is the power of
lifting state into providers.
The UI is reusable bits you compose together. The state is dependency-injected
by the provider. Swap the provider, keep the UI.
### 2.3 Lift State into Provider Components
**Impact: HIGH (enables state sharing outside component boundaries)**
Move state management into dedicated provider components. This allows sibling
components outside the main UI to access and modify state without prop drilling
or awkward refs.
**Incorrect: state trapped inside component**
```tsx
function ForwardMessageComposer() {
const [state, setState] = useState(initialState)
const forwardMessage = useForwardMessage()
return (
<Composer.Frame>
<Composer.Input />
<Composer.Footer />
</Composer.Frame>
)
}
// Problem: How does this button access composer state?
function ForwardMessageDialog() {
return (
<Dialog>
<ForwardMessageComposer />
<MessagePreview /> {/* Needs composer state */}
<DialogActions>
<CancelButton />
<ForwardButton /> {/* Needs to call submit */}
</DialogActions>
</Dialog>
)
}
```
**Incorrect: useEffect to sync state up**
```tsx
function ForwardMessageDialog() {
const [input, setInput] = useState('')
return (
<Dialog>
<ForwardMessageComposer onInputChange={setInput} />
<MessagePreview input={input} />
</Dialog>
)
}
function ForwardMessageComposer({ onInputChange }) {
const [state, setState] = useState(initialState)
useEffect(() => {
onInputChange(state.input) // Sync on every change 😬
}, [state.input])
}
```
**Incorrect: reading state from ref on submit**
```tsx
function ForwardMessageDialog() {
const stateRef = useRef(null)
return (
<Dialog>
<ForwardMessageComposer stateRef={stateRef} />
<ForwardButton onPress={() => submit(stateRef.current)} />
</Dialog>
)
}
```
**Correct: state lifted to provider**
```tsx
function ForwardMessageProvider({ children }: { children: React.ReactNode }) {
const [state, setState] = useState(initialState)
const forwardMessage = useForwardMessage()
const inputRef = useRef(null)
return (
<Composer.Provider
state={state}
actions={{ update: setState, submit: forwardMessage }}
meta={{ inputRef }}
>
{children}
</Composer.Provider>
)
}
function ForwardMessageDialog() {
return (
<ForwardMessageProvider>
<Dialog>
<ForwardMessageComposer />
<MessagePreview /> {/* Custom components can access state and actions */}
<DialogActions>
<CancelButton />
<ForwardButton /> {/* Custom components can access state and actions */}
</DialogActions>
</Dialog>
</ForwardMessageProvider>
)
}
function ForwardButton() {
const { actions } = use(Composer.Context)
return <Button onPress={actions.submit}>Forward</Button>
}
```
The ForwardButton lives outside the Composer.Frame but still has access to the
submit action because it's within the provider. Even though it's a one-off
component, it can still access the composer's state and actions from outside the
UI itself.
**Key insight:** Components that need shared state don't have to be visually
nested inside each other—they just need to be within the same provider.
---
## 3. Implementation Patterns
**Impact: MEDIUM**
Specific techniques for implementing compound components and
context providers.
### 3.1 Create Explicit Component Variants
**Impact: MEDIUM (self-documenting code, no hidden conditionals)**
Instead of one component with many boolean props, create explicit variant
components. Each variant composes the pieces it needs. The code documents
itself.
**Incorrect: one component, many modes**
```tsx
// What does this component actually render?
<Composer
isThread
isEditing={false}
channelId='abc'
showAttachments
showFormatting={false}
/>
```
**Correct: explicit variants**
```tsx
// Immediately clear what this renders
<ThreadComposer channelId="abc" />
// Or
<EditMessageComposer messageId="xyz" />
// Or
<ForwardMessageComposer messageId="123" />
```
Each implementation is unique, explicit and self-contained. Yet they can each
use shared parts.
**Implementation:**
```tsx
function ThreadComposer({ channelId }: { channelId: string }) {
return (
<ThreadProvider channelId={channelId}>
<Composer.Frame>
<Composer.Input />
<AlsoSendToChannelField channelId={channelId} />
<Composer.Footer>
<Composer.Formatting />
<Composer.Emojis />
<Composer.Submit />
</Composer.Footer>
</Composer.Frame>
</ThreadProvider>
)
}
function EditMessageComposer({ messageId }: { messageId: string }) {
return (
<EditMessageProvider messageId={messageId}>
<Composer.Frame>
<Composer.Input />
<Composer.Footer>
<Composer.Formatting />
<Composer.Emojis />
<Composer.CancelEdit />
<Composer.SaveEdit />
</Composer.Footer>
</Composer.Frame>
</EditMessageProvider>
)
}
function ForwardMessageComposer({ messageId }: { messageId: string }) {
return (
<ForwardMessageProvider messageId={messageId}>
<Composer.Frame>
<Composer.Input placeholder="Add a message, if you'd like." />
<Composer.Footer>
<Composer.Formatting />
<Composer.Emojis />
<Composer.Mentions />
</Composer.Footer>
</Composer.Frame>
</ForwardMessageProvider>
)
}
```
Each variant is explicit about:
- What provider/state it uses
- What UI elements it includes
- What actions are available
No boolean prop combinations to reason about. No impossible states.
### 3.2 Prefer Composing Children Over Render Props
**Impact: MEDIUM (cleaner composition, better readability)**
Use `children` for composition instead of `renderX` props. Children are more
readable, compose naturally, and don't require understanding callback
signatures.
**Incorrect: render props**
```tsx
function Composer({
renderHeader,
renderFooter,
renderActions,
}: {
renderHeader?: () => React.ReactNode
renderFooter?: () => React.ReactNode
renderActions?: () => React.ReactNode
}) {
return (
<form>
{renderHeader?.()}
<Input />
{renderFooter ? renderFooter() : <DefaultFooter />}
{renderActions?.()}
</form>
)
}
// Usage is awkward and inflexible
return (
<Composer
renderHeader={() => <CustomHeader />}
renderFooter={() => (
<>
<Formatting />
<Emojis />
</>
)}
renderActions={() => <SubmitButton />}
/>
)
```
**Correct: compound components with children**
```tsx
function ComposerFrame({ children }: { children: React.ReactNode }) {
return <form>{children}</form>
}
function ComposerFooter({ children }: { children: React.ReactNode }) {
return <footer className='flex'>{children}</footer>
}
// Usage is flexible
return (
<Composer.Frame>
<CustomHeader />
<Composer.Input />
<Composer.Footer>
<Composer.Formatting />
<Composer.Emojis />
<SubmitButton />
</Composer.Footer>
</Composer.Frame>
)
```
**When render props are appropriate:**
```tsx
// Render props work well when you need to pass data back
<List
data={items}
renderItem={({ item, index }) => <Item item={item} index={index} />}
/>
```
Use render props when the parent needs to provide data or state to the child.
Use children when composing static structure.
---
## 4. React 19 APIs
**Impact: MEDIUM**
React 19+ only. Don't use `forwardRef`; use `use()` instead of `useContext()`.
### 4.1 React 19 API Changes
**Impact: MEDIUM (cleaner component definitions and context usage)**
> **⚠️ React 19+ only.** Skip this if you're on React 18 or earlier.
In React 19, `ref` is now a regular prop (no `forwardRef` wrapper needed), and `use()` replaces `useContext()`.
**Incorrect: forwardRef in React 19**
```tsx
const ComposerInput = forwardRef<TextInput, Props>((props, ref) => {
return <TextInput ref={ref} {...props} />
})
```
**Correct: ref as a regular prop**
```tsx
function ComposerInput({ ref, ...props }: Props & { ref?: React.Ref<TextInput> }) {
return <TextInput ref={ref} {...props} />
}
```
**Incorrect: useContext in React 19**
```tsx
const value = useContext(MyContext)
```
**Correct: use instead of useContext**
```tsx
const value = use(MyContext)
```
`use()` can also be called conditionally, unlike `useContext()`.
---
## References
1. [https://react.dev](https://react.dev)
2. [https://react.dev/learn/passing-data-deeply-with-context](https://react.dev/learn/passing-data-deeply-with-context)
3. [https://react.dev/reference/react/use](https://react.dev/reference/react/use)

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@@ -0,0 +1,60 @@
# React Composition Patterns
A structured repository for React composition patterns that scale. These
patterns help avoid boolean prop proliferation by using compound components,
lifting state, and composing internals.
## Structure
- `rules/` - Individual rule files (one per rule)
- `_sections.md` - Section metadata (titles, impacts, descriptions)
- `_template.md` - Template for creating new rules
- `area-description.md` - Individual rule files
- `metadata.json` - Document metadata (version, organization, abstract)
- **`AGENTS.md`** - Compiled output (generated)
## Rules
### Component Architecture (CRITICAL)
- `architecture-avoid-boolean-props.md` - Don't add boolean props to customize
behavior
- `architecture-compound-components.md` - Structure as compound components with
shared context
### State Management (HIGH)
- `state-lift-state.md` - Lift state into provider components
- `state-context-interface.md` - Define clear context interfaces
(state/actions/meta)
- `state-decouple-implementation.md` - Decouple state management from UI
### Implementation Patterns (MEDIUM)
- `patterns-children-over-render-props.md` - Prefer children over renderX props
- `patterns-explicit-variants.md` - Create explicit component variants
## Core Principles
1. **Composition over configuration** — Instead of adding props, let consumers
compose
2. **Lift your state** — State in providers, not trapped in components
3. **Compose your internals** — Subcomponents access context, not props
4. **Explicit variants** — Create ThreadComposer, EditComposer, not Composer
with isThread
## Creating a New Rule
1. Copy `rules/_template.md` to `rules/area-description.md`
2. Choose the appropriate area prefix:
- `architecture-` for Component Architecture
- `state-` for State Management
- `patterns-` for Implementation Patterns
3. Fill in the frontmatter and content
4. Ensure you have clear examples with explanations
## Impact Levels
- `CRITICAL` - Foundational patterns, prevents unmaintainable code
- `HIGH` - Significant maintainability improvements
- `MEDIUM` - Good practices for cleaner code

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@@ -0,0 +1,89 @@
---
name: vercel-composition-patterns
description:
React composition patterns that scale. Use when refactoring components with
boolean prop proliferation, building flexible component libraries, or
designing reusable APIs. Triggers on tasks involving compound components,
render props, context providers, or component architecture. Includes React 19
API changes.
license: MIT
metadata:
author: vercel
version: '1.0.0'
---
# React Composition Patterns
Composition patterns for building flexible, maintainable React components. Avoid
boolean prop proliferation by using compound components, lifting state, and
composing internals. These patterns make codebases easier for both humans and AI
agents to work with as they scale.
## When to Apply
Reference these guidelines when:
- Refactoring components with many boolean props
- Building reusable component libraries
- Designing flexible component APIs
- Reviewing component architecture
- Working with compound components or context providers
## Rule Categories by Priority
| Priority | Category | Impact | Prefix |
| -------- | ----------------------- | ------ | --------------- |
| 1 | Component Architecture | HIGH | `architecture-` |
| 2 | State Management | MEDIUM | `state-` |
| 3 | Implementation Patterns | MEDIUM | `patterns-` |
| 4 | React 19 APIs | MEDIUM | `react19-` |
## Quick Reference
### 1. Component Architecture (HIGH)
- `architecture-avoid-boolean-props` - Don't add boolean props to customize
behavior; use composition
- `architecture-compound-components` - Structure complex components with shared
context
### 2. State Management (MEDIUM)
- `state-decouple-implementation` - Provider is the only place that knows how
state is managed
- `state-context-interface` - Define generic interface with state, actions, meta
for dependency injection
- `state-lift-state` - Move state into provider components for sibling access
### 3. Implementation Patterns (MEDIUM)
- `patterns-explicit-variants` - Create explicit variant components instead of
boolean modes
- `patterns-children-over-render-props` - Use children for composition instead
of renderX props
### 4. React 19 APIs (MEDIUM)
> **⚠️ React 19+ only.** Skip this section if using React 18 or earlier.
- `react19-no-forwardref` - Don't use `forwardRef`; use `use()` instead of `useContext()`
## How to Use
Read individual rule files for detailed explanations and code examples:
```
rules/architecture-avoid-boolean-props.md
rules/state-context-interface.md
```
Each rule file contains:
- Brief explanation of why it matters
- Incorrect code example with explanation
- Correct code example with explanation
- Additional context and references
## Full Compiled Document
For the complete guide with all rules expanded: `AGENTS.md`

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@@ -0,0 +1,11 @@
{
"version": "1.0.0",
"organization": "Engineering",
"date": "January 2026",
"abstract": "Composition patterns for building flexible, maintainable React components. Avoid boolean prop proliferation by using compound components, lifting state, and composing internals. These patterns make codebases easier for both humans and AI agents to work with as they scale.",
"references": [
"https://react.dev",
"https://react.dev/learn/passing-data-deeply-with-context",
"https://react.dev/reference/react/use"
]
}

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@@ -0,0 +1,29 @@
# Sections
This file defines all sections, their ordering, impact levels, and descriptions.
The section ID (in parentheses) is the filename prefix used to group rules.
---
## 1. Component Architecture (architecture)
**Impact:** HIGH
**Description:** Fundamental patterns for structuring components to avoid prop
proliferation and enable flexible composition.
## 2. State Management (state)
**Impact:** MEDIUM
**Description:** Patterns for lifting state and managing shared context across
composed components.
## 3. Implementation Patterns (patterns)
**Impact:** MEDIUM
**Description:** Specific techniques for implementing compound components and
context providers.
## 4. React 19 APIs (react19)
**Impact:** MEDIUM
**Description:** React 19+ only. Don't use `forwardRef`; use `use()` instead of `useContext()`.

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@@ -0,0 +1,24 @@
---
title: Rule Title Here
impact: MEDIUM
impactDescription: brief description of impact
tags: composition, components
---
## Rule Title Here
Brief explanation of the rule and why it matters.
**Incorrect:**
```tsx
// Bad code example
```
**Correct:**
```tsx
// Good code example
```
Reference: [Link](https://example.com)

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@@ -0,0 +1,100 @@
---
title: Avoid Boolean Prop Proliferation
impact: CRITICAL
impactDescription: prevents unmaintainable component variants
tags: composition, props, architecture
---
## Avoid Boolean Prop Proliferation
Don't add boolean props like `isThread`, `isEditing`, `isDMThread` to customize
component behavior. Each boolean doubles possible states and creates
unmaintainable conditional logic. Use composition instead.
**Incorrect (boolean props create exponential complexity):**
```tsx
function Composer({
onSubmit,
isThread,
channelId,
isDMThread,
dmId,
isEditing,
isForwarding,
}: Props) {
return (
<form>
<Header />
<Input />
{isDMThread ? (
<AlsoSendToDMField id={dmId} />
) : isThread ? (
<AlsoSendToChannelField id={channelId} />
) : null}
{isEditing ? (
<EditActions />
) : isForwarding ? (
<ForwardActions />
) : (
<DefaultActions />
)}
<Footer onSubmit={onSubmit} />
</form>
)
}
```
**Correct (composition eliminates conditionals):**
```tsx
// Channel composer
function ChannelComposer() {
return (
<Composer.Frame>
<Composer.Header />
<Composer.Input />
<Composer.Footer>
<Composer.Attachments />
<Composer.Formatting />
<Composer.Emojis />
<Composer.Submit />
</Composer.Footer>
</Composer.Frame>
)
}
// Thread composer - adds "also send to channel" field
function ThreadComposer({ channelId }: { channelId: string }) {
return (
<Composer.Frame>
<Composer.Header />
<Composer.Input />
<AlsoSendToChannelField id={channelId} />
<Composer.Footer>
<Composer.Formatting />
<Composer.Emojis />
<Composer.Submit />
</Composer.Footer>
</Composer.Frame>
)
}
// Edit composer - different footer actions
function EditComposer() {
return (
<Composer.Frame>
<Composer.Input />
<Composer.Footer>
<Composer.Formatting />
<Composer.Emojis />
<Composer.CancelEdit />
<Composer.SaveEdit />
</Composer.Footer>
</Composer.Frame>
)
}
```
Each variant is explicit about what it renders. We can share internals without
sharing a single monolithic parent.

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---
title: Use Compound Components
impact: HIGH
impactDescription: enables flexible composition without prop drilling
tags: composition, compound-components, architecture
---
## Use Compound Components
Structure complex components as compound components with a shared context. Each
subcomponent accesses shared state via context, not props. Consumers compose the
pieces they need.
**Incorrect (monolithic component with render props):**
```tsx
function Composer({
renderHeader,
renderFooter,
renderActions,
showAttachments,
showFormatting,
showEmojis,
}: Props) {
return (
<form>
{renderHeader?.()}
<Input />
{showAttachments && <Attachments />}
{renderFooter ? (
renderFooter()
) : (
<Footer>
{showFormatting && <Formatting />}
{showEmojis && <Emojis />}
{renderActions?.()}
</Footer>
)}
</form>
)
}
```
**Correct (compound components with shared context):**
```tsx
const ComposerContext = createContext<ComposerContextValue | null>(null)
function ComposerProvider({ children, state, actions, meta }: ProviderProps) {
return (
<ComposerContext value={{ state, actions, meta }}>
{children}
</ComposerContext>
)
}
function ComposerFrame({ children }: { children: React.ReactNode }) {
return <form>{children}</form>
}
function ComposerInput() {
const {
state,
actions: { update },
meta: { inputRef },
} = use(ComposerContext)
return (
<TextInput
ref={inputRef}
value={state.input}
onChangeText={(text) => update((s) => ({ ...s, input: text }))}
/>
)
}
function ComposerSubmit() {
const {
actions: { submit },
} = use(ComposerContext)
return <Button onPress={submit}>Send</Button>
}
// Export as compound component
const Composer = {
Provider: ComposerProvider,
Frame: ComposerFrame,
Input: ComposerInput,
Submit: ComposerSubmit,
Header: ComposerHeader,
Footer: ComposerFooter,
Attachments: ComposerAttachments,
Formatting: ComposerFormatting,
Emojis: ComposerEmojis,
}
```
**Usage:**
```tsx
<Composer.Provider state={state} actions={actions} meta={meta}>
<Composer.Frame>
<Composer.Header />
<Composer.Input />
<Composer.Footer>
<Composer.Formatting />
<Composer.Submit />
</Composer.Footer>
</Composer.Frame>
</Composer.Provider>
```
Consumers explicitly compose exactly what they need. No hidden conditionals. And the state, actions and meta are dependency-injected by a parent provider, allowing multiple usages of the same component structure.

View File

@@ -0,0 +1,87 @@
---
title: Prefer Composing Children Over Render Props
impact: MEDIUM
impactDescription: cleaner composition, better readability
tags: composition, children, render-props
---
## Prefer Children Over Render Props
Use `children` for composition instead of `renderX` props. Children are more
readable, compose naturally, and don't require understanding callback
signatures.
**Incorrect (render props):**
```tsx
function Composer({
renderHeader,
renderFooter,
renderActions,
}: {
renderHeader?: () => React.ReactNode
renderFooter?: () => React.ReactNode
renderActions?: () => React.ReactNode
}) {
return (
<form>
{renderHeader?.()}
<Input />
{renderFooter ? renderFooter() : <DefaultFooter />}
{renderActions?.()}
</form>
)
}
// Usage is awkward and inflexible
return (
<Composer
renderHeader={() => <CustomHeader />}
renderFooter={() => (
<>
<Formatting />
<Emojis />
</>
)}
renderActions={() => <SubmitButton />}
/>
)
```
**Correct (compound components with children):**
```tsx
function ComposerFrame({ children }: { children: React.ReactNode }) {
return <form>{children}</form>
}
function ComposerFooter({ children }: { children: React.ReactNode }) {
return <footer className='flex'>{children}</footer>
}
// Usage is flexible
return (
<Composer.Frame>
<CustomHeader />
<Composer.Input />
<Composer.Footer>
<Composer.Formatting />
<Composer.Emojis />
<SubmitButton />
</Composer.Footer>
</Composer.Frame>
)
```
**When render props are appropriate:**
```tsx
// Render props work well when you need to pass data back
<List
data={items}
renderItem={({ item, index }) => <Item item={item} index={index} />}
/>
```
Use render props when the parent needs to provide data or state to the child.
Use children when composing static structure.

View File

@@ -0,0 +1,100 @@
---
title: Create Explicit Component Variants
impact: MEDIUM
impactDescription: self-documenting code, no hidden conditionals
tags: composition, variants, architecture
---
## Create Explicit Component Variants
Instead of one component with many boolean props, create explicit variant
components. Each variant composes the pieces it needs. The code documents
itself.
**Incorrect (one component, many modes):**
```tsx
// What does this component actually render?
<Composer
isThread
isEditing={false}
channelId='abc'
showAttachments
showFormatting={false}
/>
```
**Correct (explicit variants):**
```tsx
// Immediately clear what this renders
<ThreadComposer channelId="abc" />
// Or
<EditMessageComposer messageId="xyz" />
// Or
<ForwardMessageComposer messageId="123" />
```
Each implementation is unique, explicit and self-contained. Yet they can each
use shared parts.
**Implementation:**
```tsx
function ThreadComposer({ channelId }: { channelId: string }) {
return (
<ThreadProvider channelId={channelId}>
<Composer.Frame>
<Composer.Input />
<AlsoSendToChannelField channelId={channelId} />
<Composer.Footer>
<Composer.Formatting />
<Composer.Emojis />
<Composer.Submit />
</Composer.Footer>
</Composer.Frame>
</ThreadProvider>
)
}
function EditMessageComposer({ messageId }: { messageId: string }) {
return (
<EditMessageProvider messageId={messageId}>
<Composer.Frame>
<Composer.Input />
<Composer.Footer>
<Composer.Formatting />
<Composer.Emojis />
<Composer.CancelEdit />
<Composer.SaveEdit />
</Composer.Footer>
</Composer.Frame>
</EditMessageProvider>
)
}
function ForwardMessageComposer({ messageId }: { messageId: string }) {
return (
<ForwardMessageProvider messageId={messageId}>
<Composer.Frame>
<Composer.Input placeholder="Add a message, if you'd like." />
<Composer.Footer>
<Composer.Formatting />
<Composer.Emojis />
<Composer.Mentions />
</Composer.Footer>
</Composer.Frame>
</ForwardMessageProvider>
)
}
```
Each variant is explicit about:
- What provider/state it uses
- What UI elements it includes
- What actions are available
No boolean prop combinations to reason about. No impossible states.

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@@ -0,0 +1,42 @@
---
title: React 19 API Changes
impact: MEDIUM
impactDescription: cleaner component definitions and context usage
tags: react19, refs, context, hooks
---
## React 19 API Changes
> **⚠️ React 19+ only.** Skip this if you're on React 18 or earlier.
In React 19, `ref` is now a regular prop (no `forwardRef` wrapper needed), and `use()` replaces `useContext()`.
**Incorrect (forwardRef in React 19):**
```tsx
const ComposerInput = forwardRef<TextInput, Props>((props, ref) => {
return <TextInput ref={ref} {...props} />
})
```
**Correct (ref as a regular prop):**
```tsx
function ComposerInput({ ref, ...props }: Props & { ref?: React.Ref<TextInput> }) {
return <TextInput ref={ref} {...props} />
}
```
**Incorrect (useContext in React 19):**
```tsx
const value = useContext(MyContext)
```
**Correct (use instead of useContext):**
```tsx
const value = use(MyContext)
```
`use()` can also be called conditionally, unlike `useContext()`.

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@@ -0,0 +1,191 @@
---
title: Define Generic Context Interfaces for Dependency Injection
impact: HIGH
impactDescription: enables dependency-injectable state across use-cases
tags: composition, context, state, typescript, dependency-injection
---
## Define Generic Context Interfaces for Dependency Injection
Define a **generic interface** for your component context with three parts:
`state`, `actions`, and `meta`. This interface is a contract that any provider
can implement—enabling the same UI components to work with completely different
state implementations.
**Core principle:** Lift state, compose internals, make state
dependency-injectable.
**Incorrect (UI coupled to specific state implementation):**
```tsx
function ComposerInput() {
// Tightly coupled to a specific hook
const { input, setInput } = useChannelComposerState()
return <TextInput value={input} onChangeText={setInput} />
}
```
**Correct (generic interface enables dependency injection):**
```tsx
// Define a GENERIC interface that any provider can implement
interface ComposerState {
input: string
attachments: Attachment[]
isSubmitting: boolean
}
interface ComposerActions {
update: (updater: (state: ComposerState) => ComposerState) => void
submit: () => void
}
interface ComposerMeta {
inputRef: React.RefObject<TextInput>
}
interface ComposerContextValue {
state: ComposerState
actions: ComposerActions
meta: ComposerMeta
}
const ComposerContext = createContext<ComposerContextValue | null>(null)
```
**UI components consume the interface, not the implementation:**
```tsx
function ComposerInput() {
const {
state,
actions: { update },
meta,
} = use(ComposerContext)
// This component works with ANY provider that implements the interface
return (
<TextInput
ref={meta.inputRef}
value={state.input}
onChangeText={(text) => update((s) => ({ ...s, input: text }))}
/>
)
}
```
**Different providers implement the same interface:**
```tsx
// Provider A: Local state for ephemeral forms
function ForwardMessageProvider({ children }: { children: React.ReactNode }) {
const [state, setState] = useState(initialState)
const inputRef = useRef(null)
const submit = useForwardMessage()
return (
<ComposerContext
value={{
state,
actions: { update: setState, submit },
meta: { inputRef },
}}
>
{children}
</ComposerContext>
)
}
// Provider B: Global synced state for channels
function ChannelProvider({ channelId, children }: Props) {
const { state, update, submit } = useGlobalChannel(channelId)
const inputRef = useRef(null)
return (
<ComposerContext
value={{
state,
actions: { update, submit },
meta: { inputRef },
}}
>
{children}
</ComposerContext>
)
}
```
**The same composed UI works with both:**
```tsx
// Works with ForwardMessageProvider (local state)
<ForwardMessageProvider>
<Composer.Frame>
<Composer.Input />
<Composer.Submit />
</Composer.Frame>
</ForwardMessageProvider>
// Works with ChannelProvider (global synced state)
<ChannelProvider channelId="abc">
<Composer.Frame>
<Composer.Input />
<Composer.Submit />
</Composer.Frame>
</ChannelProvider>
```
**Custom UI outside the component can access state and actions:**
The provider boundary is what matters—not the visual nesting. Components that
need shared state don't have to be inside the `Composer.Frame`. They just need
to be within the provider.
```tsx
function ForwardMessageDialog() {
return (
<ForwardMessageProvider>
<Dialog>
{/* The composer UI */}
<Composer.Frame>
<Composer.Input placeholder="Add a message, if you'd like." />
<Composer.Footer>
<Composer.Formatting />
<Composer.Emojis />
</Composer.Footer>
</Composer.Frame>
{/* Custom UI OUTSIDE the composer, but INSIDE the provider */}
<MessagePreview />
{/* Actions at the bottom of the dialog */}
<DialogActions>
<CancelButton />
<ForwardButton />
</DialogActions>
</Dialog>
</ForwardMessageProvider>
)
}
// This button lives OUTSIDE Composer.Frame but can still submit based on its context!
function ForwardButton() {
const {
actions: { submit },
} = use(ComposerContext)
return <Button onPress={submit}>Forward</Button>
}
// This preview lives OUTSIDE Composer.Frame but can read composer's state!
function MessagePreview() {
const { state } = use(ComposerContext)
return <Preview message={state.input} attachments={state.attachments} />
}
```
The `ForwardButton` and `MessagePreview` are not visually inside the composer
box, but they can still access its state and actions. This is the power of
lifting state into providers.
The UI is reusable bits you compose together. The state is dependency-injected
by the provider. Swap the provider, keep the UI.

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@@ -0,0 +1,113 @@
---
title: Decouple State Management from UI
impact: MEDIUM
impactDescription: enables swapping state implementations without changing UI
tags: composition, state, architecture
---
## Decouple State Management from UI
The provider component should be the only place that knows how state is managed.
UI components consume the context interface—they don't know if state comes from
useState, Zustand, or a server sync.
**Incorrect (UI coupled to state implementation):**
```tsx
function ChannelComposer({ channelId }: { channelId: string }) {
// UI component knows about global state implementation
const state = useGlobalChannelState(channelId)
const { submit, updateInput } = useChannelSync(channelId)
return (
<Composer.Frame>
<Composer.Input
value={state.input}
onChange={(text) => sync.updateInput(text)}
/>
<Composer.Submit onPress={() => sync.submit()} />
</Composer.Frame>
)
}
```
**Correct (state management isolated in provider):**
```tsx
// Provider handles all state management details
function ChannelProvider({
channelId,
children,
}: {
channelId: string
children: React.ReactNode
}) {
const { state, update, submit } = useGlobalChannel(channelId)
const inputRef = useRef(null)
return (
<Composer.Provider
state={state}
actions={{ update, submit }}
meta={{ inputRef }}
>
{children}
</Composer.Provider>
)
}
// UI component only knows about the context interface
function ChannelComposer() {
return (
<Composer.Frame>
<Composer.Header />
<Composer.Input />
<Composer.Footer>
<Composer.Submit />
</Composer.Footer>
</Composer.Frame>
)
}
// Usage
function Channel({ channelId }: { channelId: string }) {
return (
<ChannelProvider channelId={channelId}>
<ChannelComposer />
</ChannelProvider>
)
}
```
**Different providers, same UI:**
```tsx
// Local state for ephemeral forms
function ForwardMessageProvider({ children }) {
const [state, setState] = useState(initialState)
const forwardMessage = useForwardMessage()
return (
<Composer.Provider
state={state}
actions={{ update: setState, submit: forwardMessage }}
>
{children}
</Composer.Provider>
)
}
// Global synced state for channels
function ChannelProvider({ channelId, children }) {
const { state, update, submit } = useGlobalChannel(channelId)
return (
<Composer.Provider state={state} actions={{ update, submit }}>
{children}
</Composer.Provider>
)
}
```
The same `Composer.Input` component works with both providers because it only
depends on the context interface, not the implementation.

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@@ -0,0 +1,125 @@
---
title: Lift State into Provider Components
impact: HIGH
impactDescription: enables state sharing outside component boundaries
tags: composition, state, context, providers
---
## Lift State into Provider Components
Move state management into dedicated provider components. This allows sibling
components outside the main UI to access and modify state without prop drilling
or awkward refs.
**Incorrect (state trapped inside component):**
```tsx
function ForwardMessageComposer() {
const [state, setState] = useState(initialState)
const forwardMessage = useForwardMessage()
return (
<Composer.Frame>
<Composer.Input />
<Composer.Footer />
</Composer.Frame>
)
}
// Problem: How does this button access composer state?
function ForwardMessageDialog() {
return (
<Dialog>
<ForwardMessageComposer />
<MessagePreview /> {/* Needs composer state */}
<DialogActions>
<CancelButton />
<ForwardButton /> {/* Needs to call submit */}
</DialogActions>
</Dialog>
)
}
```
**Incorrect (useEffect to sync state up):**
```tsx
function ForwardMessageDialog() {
const [input, setInput] = useState('')
return (
<Dialog>
<ForwardMessageComposer onInputChange={setInput} />
<MessagePreview input={input} />
</Dialog>
)
}
function ForwardMessageComposer({ onInputChange }) {
const [state, setState] = useState(initialState)
useEffect(() => {
onInputChange(state.input) // Sync on every change 😬
}, [state.input])
}
```
**Incorrect (reading state from ref on submit):**
```tsx
function ForwardMessageDialog() {
const stateRef = useRef(null)
return (
<Dialog>
<ForwardMessageComposer stateRef={stateRef} />
<ForwardButton onPress={() => submit(stateRef.current)} />
</Dialog>
)
}
```
**Correct (state lifted to provider):**
```tsx
function ForwardMessageProvider({ children }: { children: React.ReactNode }) {
const [state, setState] = useState(initialState)
const forwardMessage = useForwardMessage()
const inputRef = useRef(null)
return (
<Composer.Provider
state={state}
actions={{ update: setState, submit: forwardMessage }}
meta={{ inputRef }}
>
{children}
</Composer.Provider>
)
}
function ForwardMessageDialog() {
return (
<ForwardMessageProvider>
<Dialog>
<ForwardMessageComposer />
<MessagePreview /> {/* Custom components can access state and actions */}
<DialogActions>
<CancelButton />
<ForwardButton /> {/* Custom components can access state and actions */}
</DialogActions>
</Dialog>
</ForwardMessageProvider>
)
}
function ForwardButton() {
const { actions } = use(Composer.Context)
return <Button onPress={actions.submit}>Forward</Button>
}
```
The ForwardButton lives outside the Composer.Frame but still has access to the
submit action because it's within the provider. Even though it's a one-off
component, it can still access the composer's state and actions from outside the
UI itself.
**Key insight:** Components that need shared state don't have to be visually
nested inside each other—they just need to be within the same provider.

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# React Best Practices
A structured repository for creating and maintaining React Best Practices optimized for agents and LLMs.
## Structure
- `rules/` - Individual rule files (one per rule)
- `_sections.md` - Section metadata (titles, impacts, descriptions)
- `_template.md` - Template for creating new rules
- `area-description.md` - Individual rule files
- `src/` - Build scripts and utilities
- `metadata.json` - Document metadata (version, organization, abstract)
- __`AGENTS.md`__ - Compiled output (generated)
- __`test-cases.json`__ - Test cases for LLM evaluation (generated)
## Getting Started
1. Install dependencies:
```bash
pnpm install
```
2. Build AGENTS.md from rules:
```bash
pnpm build
```
3. Validate rule files:
```bash
pnpm validate
```
4. Extract test cases:
```bash
pnpm extract-tests
```
## Creating a New Rule
1. Copy `rules/_template.md` to `rules/area-description.md`
2. Choose the appropriate area prefix:
- `async-` for Eliminating Waterfalls (Section 1)
- `bundle-` for Bundle Size Optimization (Section 2)
- `server-` for Server-Side Performance (Section 3)
- `client-` for Client-Side Data Fetching (Section 4)
- `rerender-` for Re-render Optimization (Section 5)
- `rendering-` for Rendering Performance (Section 6)
- `js-` for JavaScript Performance (Section 7)
- `advanced-` for Advanced Patterns (Section 8)
3. Fill in the frontmatter and content
4. Ensure you have clear examples with explanations
5. Run `pnpm build` to regenerate AGENTS.md and test-cases.json
## Rule File Structure
Each rule file should follow this structure:
```markdown
---
title: Rule Title Here
impact: MEDIUM
impactDescription: Optional description
tags: tag1, tag2, tag3
---
## Rule Title Here
Brief explanation of the rule and why it matters.
**Incorrect (description of what's wrong):**
```typescript
// Bad code example
```
**Correct (description of what's right):**
```typescript
// Good code example
```
Optional explanatory text after examples.
Reference: [Link](https://example.com)
## File Naming Convention
- Files starting with `_` are special (excluded from build)
- Rule files: `area-description.md` (e.g., `async-parallel.md`)
- Section is automatically inferred from filename prefix
- Rules are sorted alphabetically by title within each section
- IDs (e.g., 1.1, 1.2) are auto-generated during build
## Impact Levels
- `CRITICAL` - Highest priority, major performance gains
- `HIGH` - Significant performance improvements
- `MEDIUM-HIGH` - Moderate-high gains
- `MEDIUM` - Moderate performance improvements
- `LOW-MEDIUM` - Low-medium gains
- `LOW` - Incremental improvements
## Scripts
- `pnpm build` - Compile rules into AGENTS.md
- `pnpm validate` - Validate all rule files
- `pnpm extract-tests` - Extract test cases for LLM evaluation
- `pnpm dev` - Build and validate
## Contributing
When adding or modifying rules:
1. Use the correct filename prefix for your section
2. Follow the `_template.md` structure
3. Include clear bad/good examples with explanations
4. Add appropriate tags
5. Run `pnpm build` to regenerate AGENTS.md and test-cases.json
6. Rules are automatically sorted by title - no need to manage numbers!
## Acknowledgments
Originally created by [@shuding](https://x.com/shuding) at [Vercel](https://vercel.com).

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@@ -0,0 +1,149 @@
---
name: vercel-react-best-practices
description: React and Next.js performance optimization guidelines from Vercel Engineering. This skill should be used when writing, reviewing, or refactoring React/Next.js code to ensure optimal performance patterns. Triggers on tasks involving React components, Next.js pages, data fetching, bundle optimization, or performance improvements.
license: MIT
metadata:
author: vercel
version: "1.0.0"
---
# Vercel React Best Practices
Comprehensive performance optimization guide for React and Next.js applications, maintained by Vercel. Contains 70 rules across 8 categories, prioritized by impact to guide automated refactoring and code generation.
## When to Apply
Reference these guidelines when:
- Writing new React components or Next.js pages
- Implementing data fetching (client or server-side)
- Reviewing code for performance issues
- Refactoring existing React/Next.js code
- Optimizing bundle size or load times
## Rule Categories by Priority
| Priority | Category | Impact | Prefix |
|----------|----------|--------|--------|
| 1 | Eliminating Waterfalls | CRITICAL | `async-` |
| 2 | Bundle Size Optimization | CRITICAL | `bundle-` |
| 3 | Server-Side Performance | HIGH | `server-` |
| 4 | Client-Side Data Fetching | MEDIUM-HIGH | `client-` |
| 5 | Re-render Optimization | MEDIUM | `rerender-` |
| 6 | Rendering Performance | MEDIUM | `rendering-` |
| 7 | JavaScript Performance | LOW-MEDIUM | `js-` |
| 8 | Advanced Patterns | LOW | `advanced-` |
## Quick Reference
### 1. Eliminating Waterfalls (CRITICAL)
- `async-cheap-condition-before-await` - Check cheap sync conditions before awaiting flags or remote values
- `async-defer-await` - Move await into branches where actually used
- `async-parallel` - Use Promise.all() for independent operations
- `async-dependencies` - Use better-all for partial dependencies
- `async-api-routes` - Start promises early, await late in API routes
- `async-suspense-boundaries` - Use Suspense to stream content
### 2. Bundle Size Optimization (CRITICAL)
- `bundle-barrel-imports` - Import directly, avoid barrel files
- `bundle-analyzable-paths` - Prefer statically analyzable import and file-system paths to avoid broad bundles and traces
- `bundle-dynamic-imports` - Use next/dynamic for heavy components
- `bundle-defer-third-party` - Load analytics/logging after hydration
- `bundle-conditional` - Load modules only when feature is activated
- `bundle-preload` - Preload on hover/focus for perceived speed
### 3. Server-Side Performance (HIGH)
- `server-auth-actions` - Authenticate server actions like API routes
- `server-cache-react` - Use React.cache() for per-request deduplication
- `server-cache-lru` - Use LRU cache for cross-request caching
- `server-dedup-props` - Avoid duplicate serialization in RSC props
- `server-hoist-static-io` - Hoist static I/O (fonts, logos) to module level
- `server-no-shared-module-state` - Avoid module-level mutable request state in RSC/SSR
- `server-serialization` - Minimize data passed to client components
- `server-parallel-fetching` - Restructure components to parallelize fetches
- `server-parallel-nested-fetching` - Chain nested fetches per item in Promise.all
- `server-after-nonblocking` - Use after() for non-blocking operations
### 4. Client-Side Data Fetching (MEDIUM-HIGH)
- `client-swr-dedup` - Use SWR for automatic request deduplication
- `client-event-listeners` - Deduplicate global event listeners
- `client-passive-event-listeners` - Use passive listeners for scroll
- `client-localstorage-schema` - Version and minimize localStorage data
### 5. Re-render Optimization (MEDIUM)
- `rerender-defer-reads` - Don't subscribe to state only used in callbacks
- `rerender-memo` - Extract expensive work into memoized components
- `rerender-memo-with-default-value` - Hoist default non-primitive props
- `rerender-dependencies` - Use primitive dependencies in effects
- `rerender-derived-state` - Subscribe to derived booleans, not raw values
- `rerender-derived-state-no-effect` - Derive state during render, not effects
- `rerender-functional-setstate` - Use functional setState for stable callbacks
- `rerender-lazy-state-init` - Pass function to useState for expensive values
- `rerender-simple-expression-in-memo` - Avoid memo for simple primitives
- `rerender-split-combined-hooks` - Split hooks with independent dependencies
- `rerender-move-effect-to-event` - Put interaction logic in event handlers
- `rerender-transitions` - Use startTransition for non-urgent updates
- `rerender-use-deferred-value` - Defer expensive renders to keep input responsive
- `rerender-use-ref-transient-values` - Use refs for transient frequent values
- `rerender-no-inline-components` - Don't define components inside components
### 6. Rendering Performance (MEDIUM)
- `rendering-animate-svg-wrapper` - Animate div wrapper, not SVG element
- `rendering-content-visibility` - Use content-visibility for long lists
- `rendering-hoist-jsx` - Extract static JSX outside components
- `rendering-svg-precision` - Reduce SVG coordinate precision
- `rendering-hydration-no-flicker` - Use inline script for client-only data
- `rendering-hydration-suppress-warning` - Suppress expected mismatches
- `rendering-activity` - Use Activity component for show/hide
- `rendering-conditional-render` - Use ternary, not && for conditionals
- `rendering-usetransition-loading` - Prefer useTransition for loading state
- `rendering-resource-hints` - Use React DOM resource hints for preloading
- `rendering-script-defer-async` - Use defer or async on script tags
### 7. JavaScript Performance (LOW-MEDIUM)
- `js-batch-dom-css` - Group CSS changes via classes or cssText
- `js-index-maps` - Build Map for repeated lookups
- `js-cache-property-access` - Cache object properties in loops
- `js-cache-function-results` - Cache function results in module-level Map
- `js-cache-storage` - Cache localStorage/sessionStorage reads
- `js-combine-iterations` - Combine multiple filter/map into one loop
- `js-length-check-first` - Check array length before expensive comparison
- `js-early-exit` - Return early from functions
- `js-hoist-regexp` - Hoist RegExp creation outside loops
- `js-min-max-loop` - Use loop for min/max instead of sort
- `js-set-map-lookups` - Use Set/Map for O(1) lookups
- `js-tosorted-immutable` - Use toSorted() for immutability
- `js-flatmap-filter` - Use flatMap to map and filter in one pass
- `js-request-idle-callback` - Defer non-critical work to browser idle time
### 8. Advanced Patterns (LOW)
- `advanced-effect-event-deps` - Don't put `useEffectEvent` results in effect deps
- `advanced-event-handler-refs` - Store event handlers in refs
- `advanced-init-once` - Initialize app once per app load
- `advanced-use-latest` - useLatest for stable callback refs
## How to Use
Read individual rule files for detailed explanations and code examples:
```
rules/async-parallel.md
rules/bundle-barrel-imports.md
```
Each rule file contains:
- Brief explanation of why it matters
- Incorrect code example with explanation
- Correct code example with explanation
- Additional context and references
## Full Compiled Document
For the complete guide with all rules expanded: `AGENTS.md`

View File

@@ -0,0 +1,15 @@
{
"version": "1.0.0",
"organization": "Vercel Engineering",
"date": "January 2026",
"abstract": "Comprehensive performance optimization guide for React and Next.js applications, designed for AI agents and LLMs. Contains 40+ rules across 8 categories, prioritized by impact from critical (eliminating waterfalls, reducing bundle size) to incremental (advanced patterns). Each rule includes detailed explanations, real-world examples comparing incorrect vs. correct implementations, and specific impact metrics to guide automated refactoring and code generation.",
"references": [
"https://react.dev",
"https://nextjs.org",
"https://swr.vercel.app",
"https://github.com/shuding/better-all",
"https://github.com/isaacs/node-lru-cache",
"https://vercel.com/blog/how-we-optimized-package-imports-in-next-js",
"https://vercel.com/blog/how-we-made-the-vercel-dashboard-twice-as-fast"
]
}

View File

@@ -0,0 +1,46 @@
# Sections
This file defines all sections, their ordering, impact levels, and descriptions.
The section ID (in parentheses) is the filename prefix used to group rules.
---
## 1. Eliminating Waterfalls (async)
**Impact:** CRITICAL
**Description:** Waterfalls are the #1 performance killer. Each sequential await adds full network latency. Eliminating them yields the largest gains.
## 2. Bundle Size Optimization (bundle)
**Impact:** CRITICAL
**Description:** Reducing initial bundle size improves Time to Interactive and Largest Contentful Paint.
## 3. Server-Side Performance (server)
**Impact:** HIGH
**Description:** Optimizing server-side rendering and data fetching eliminates server-side waterfalls and reduces response times.
## 4. Client-Side Data Fetching (client)
**Impact:** MEDIUM-HIGH
**Description:** Automatic deduplication and efficient data fetching patterns reduce redundant network requests.
## 5. Re-render Optimization (rerender)
**Impact:** MEDIUM
**Description:** Reducing unnecessary re-renders minimizes wasted computation and improves UI responsiveness.
## 6. Rendering Performance (rendering)
**Impact:** MEDIUM
**Description:** Optimizing the rendering process reduces the work the browser needs to do.
## 7. JavaScript Performance (js)
**Impact:** LOW-MEDIUM
**Description:** Micro-optimizations for hot paths can add up to meaningful improvements.
## 8. Advanced Patterns (advanced)
**Impact:** LOW
**Description:** Advanced patterns for specific cases that require careful implementation.

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---
title: Rule Title Here
impact: MEDIUM
impactDescription: Optional description of impact (e.g., "20-50% improvement")
tags: tag1, tag2
---
## Rule Title Here
**Impact: MEDIUM (optional impact description)**
Brief explanation of the rule and why it matters. This should be clear and concise, explaining the performance implications.
**Incorrect (description of what's wrong):**
```typescript
// Bad code example here
const bad = example()
```
**Correct (description of what's right):**
```typescript
// Good code example here
const good = example()
```
Reference: [Link to documentation or resource](https://example.com)

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@@ -0,0 +1,56 @@
---
title: Do Not Put Effect Events in Dependency Arrays
impact: LOW
impactDescription: avoids unnecessary effect re-runs and lint errors
tags: advanced, hooks, useEffectEvent, dependencies, effects
---
## Do Not Put Effect Events in Dependency Arrays
Effect Event functions do not have a stable identity. Their identity intentionally changes on every render. Do not include the function returned by `useEffectEvent` in a `useEffect` dependency array. Keep the actual reactive values as dependencies and call the Effect Event from inside the effect body or subscriptions created by that effect.
**Incorrect (Effect Event added as a dependency):**
```tsx
import { useEffect, useEffectEvent } from 'react'
function ChatRoom({ roomId, onConnected }: {
roomId: string
onConnected: () => void
}) {
const handleConnected = useEffectEvent(onConnected)
useEffect(() => {
const connection = createConnection(roomId)
connection.on('connected', handleConnected)
connection.connect()
return () => connection.disconnect()
}, [roomId, handleConnected])
}
```
Including the Effect Event in dependencies makes the effect re-run every render and triggers the React Hooks lint rule.
**Correct (depend on reactive values, not the Effect Event):**
```tsx
import { useEffect, useEffectEvent } from 'react'
function ChatRoom({ roomId, onConnected }: {
roomId: string
onConnected: () => void
}) {
const handleConnected = useEffectEvent(onConnected)
useEffect(() => {
const connection = createConnection(roomId)
connection.on('connected', handleConnected)
connection.connect()
return () => connection.disconnect()
}, [roomId])
}
```
Reference: [React useEffectEvent: Effect Event in deps](https://react.dev/reference/react/useEffectEvent#effect-event-in-deps)

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---
title: Store Event Handlers in Refs
impact: LOW
impactDescription: stable subscriptions
tags: advanced, hooks, refs, event-handlers, optimization
---
## Store Event Handlers in Refs
Store callbacks in refs when used in effects that shouldn't re-subscribe on callback changes.
**Incorrect (re-subscribes on every render):**
```tsx
function useWindowEvent(event: string, handler: (e) => void) {
useEffect(() => {
window.addEventListener(event, handler)
return () => window.removeEventListener(event, handler)
}, [event, handler])
}
```
**Correct (stable subscription):**
```tsx
function useWindowEvent(event: string, handler: (e) => void) {
const handlerRef = useRef(handler)
useEffect(() => {
handlerRef.current = handler
}, [handler])
useEffect(() => {
const listener = (e) => handlerRef.current(e)
window.addEventListener(event, listener)
return () => window.removeEventListener(event, listener)
}, [event])
}
```
**Alternative: use `useEffectEvent` if you're on latest React:**
```tsx
import { useEffectEvent } from 'react'
function useWindowEvent(event: string, handler: (e) => void) {
const onEvent = useEffectEvent(handler)
useEffect(() => {
window.addEventListener(event, onEvent)
return () => window.removeEventListener(event, onEvent)
}, [event])
}
```
`useEffectEvent` provides a cleaner API for the same pattern: it creates a stable function reference that always calls the latest version of the handler.

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---
title: Initialize App Once, Not Per Mount
impact: LOW-MEDIUM
impactDescription: avoids duplicate init in development
tags: initialization, useEffect, app-startup, side-effects
---
## Initialize App Once, Not Per Mount
Do not put app-wide initialization that must run once per app load inside `useEffect([])` of a component. Components can remount and effects will re-run. Use a module-level guard or top-level init in the entry module instead.
**Incorrect (runs twice in dev, re-runs on remount):**
```tsx
function Comp() {
useEffect(() => {
loadFromStorage()
checkAuthToken()
}, [])
// ...
}
```
**Correct (once per app load):**
```tsx
let didInit = false
function Comp() {
useEffect(() => {
if (didInit) return
didInit = true
loadFromStorage()
checkAuthToken()
}, [])
// ...
}
```
Reference: [Initializing the application](https://react.dev/learn/you-might-not-need-an-effect#initializing-the-application)

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---
title: useEffectEvent for Stable Callback Refs
impact: LOW
impactDescription: prevents effect re-runs
tags: advanced, hooks, useEffectEvent, refs, optimization
---
## useEffectEvent for Stable Callback Refs
Access latest values in callbacks without adding them to dependency arrays. Prevents effect re-runs while avoiding stale closures.
**Incorrect (effect re-runs on every callback change):**
```tsx
function SearchInput({ onSearch }: { onSearch: (q: string) => void }) {
const [query, setQuery] = useState('')
useEffect(() => {
const timeout = setTimeout(() => onSearch(query), 300)
return () => clearTimeout(timeout)
}, [query, onSearch])
}
```
**Correct (using React's useEffectEvent):**
```tsx
import { useEffectEvent } from 'react';
function SearchInput({ onSearch }: { onSearch: (q: string) => void }) {
const [query, setQuery] = useState('')
const onSearchEvent = useEffectEvent(onSearch)
useEffect(() => {
const timeout = setTimeout(() => onSearchEvent(query), 300)
return () => clearTimeout(timeout)
}, [query])
}
```

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---
title: Prevent Waterfall Chains in API Routes
impact: CRITICAL
impactDescription: 2-10× improvement
tags: api-routes, server-actions, waterfalls, parallelization
---
## Prevent Waterfall Chains in API Routes
In API routes and Server Actions, start independent operations immediately, even if you don't await them yet.
**Incorrect (config waits for auth, data waits for both):**
```typescript
export async function GET(request: Request) {
const session = await auth()
const config = await fetchConfig()
const data = await fetchData(session.user.id)
return Response.json({ data, config })
}
```
**Correct (auth and config start immediately):**
```typescript
export async function GET(request: Request) {
const sessionPromise = auth()
const configPromise = fetchConfig()
const session = await sessionPromise
const [config, data] = await Promise.all([
configPromise,
fetchData(session.user.id)
])
return Response.json({ data, config })
}
```
For operations with more complex dependency chains, use `better-all` to automatically maximize parallelism (see Dependency-Based Parallelization).

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---
title: Check Cheap Conditions Before Async Flags
impact: HIGH
impactDescription: avoids unnecessary async work when a synchronous guard already fails
tags: async, await, feature-flags, short-circuit, conditional
---
## Check Cheap Conditions Before Async Flags
When a branch uses `await` for a flag or remote value and also requires a **cheap synchronous** condition (local props, request metadata, already-loaded state), evaluate the cheap condition **first**. Otherwise you pay for the async call even when the compound condition can never be true.
This is a specialization of [Defer Await Until Needed](./async-defer-await.md) for `flag && cheapCondition` style checks.
**Incorrect:**
```typescript
const someFlag = await getFlag()
if (someFlag && someCondition) {
// ...
}
```
**Correct:**
```typescript
if (someCondition) {
const someFlag = await getFlag()
if (someFlag) {
// ...
}
}
```
This matters when `getFlag` hits the network, a feature-flag service, or `React.cache` / DB work: skipping it when `someCondition` is false removes that cost on the cold path.
Keep the original order if `someCondition` is expensive, depends on the flag, or you must run side effects in a fixed order.

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---
title: Defer Await Until Needed
impact: HIGH
impactDescription: avoids blocking unused code paths
tags: async, await, conditional, optimization
---
## Defer Await Until Needed
Move `await` operations into the branches where they're actually used to avoid blocking code paths that don't need them.
**Incorrect (blocks both branches):**
```typescript
async function handleRequest(userId: string, skipProcessing: boolean) {
const userData = await fetchUserData(userId)
if (skipProcessing) {
// Returns immediately but still waited for userData
return { skipped: true }
}
// Only this branch uses userData
return processUserData(userData)
}
```
**Correct (only blocks when needed):**
```typescript
async function handleRequest(userId: string, skipProcessing: boolean) {
if (skipProcessing) {
// Returns immediately without waiting
return { skipped: true }
}
// Fetch only when needed
const userData = await fetchUserData(userId)
return processUserData(userData)
}
```
**Another example (early return optimization):**
```typescript
// Incorrect: always fetches permissions
async function updateResource(resourceId: string, userId: string) {
const permissions = await fetchPermissions(userId)
const resource = await getResource(resourceId)
if (!resource) {
return { error: 'Not found' }
}
if (!permissions.canEdit) {
return { error: 'Forbidden' }
}
return await updateResourceData(resource, permissions)
}
// Correct: fetches only when needed
async function updateResource(resourceId: string, userId: string) {
const resource = await getResource(resourceId)
if (!resource) {
return { error: 'Not found' }
}
const permissions = await fetchPermissions(userId)
if (!permissions.canEdit) {
return { error: 'Forbidden' }
}
return await updateResourceData(resource, permissions)
}
```
This optimization is especially valuable when the skipped branch is frequently taken, or when the deferred operation is expensive.
For `await getFlag()` combined with a cheap synchronous guard (`flag && someCondition`), see [Check Cheap Conditions Before Async Flags](./async-cheap-condition-before-await.md).

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---
title: Dependency-Based Parallelization
impact: CRITICAL
impactDescription: 2-10× improvement
tags: async, parallelization, dependencies, better-all
---
## Dependency-Based Parallelization
For operations with partial dependencies, use `better-all` to maximize parallelism. It automatically starts each task at the earliest possible moment.
**Incorrect (profile waits for config unnecessarily):**
```typescript
const [user, config] = await Promise.all([
fetchUser(),
fetchConfig()
])
const profile = await fetchProfile(user.id)
```
**Correct (config and profile run in parallel):**
```typescript
import { all } from 'better-all'
const { user, config, profile } = await all({
async user() { return fetchUser() },
async config() { return fetchConfig() },
async profile() {
return fetchProfile((await this.$.user).id)
}
})
```
**Alternative without extra dependencies:**
We can also create all the promises first, and do `Promise.all()` at the end.
```typescript
const userPromise = fetchUser()
const profilePromise = userPromise.then(user => fetchProfile(user.id))
const [user, config, profile] = await Promise.all([
userPromise,
fetchConfig(),
profilePromise
])
```
Reference: [https://github.com/shuding/better-all](https://github.com/shuding/better-all)

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---
title: Promise.all() for Independent Operations
impact: CRITICAL
impactDescription: 2-10× improvement
tags: async, parallelization, promises, waterfalls
---
## Promise.all() for Independent Operations
When async operations have no interdependencies, execute them concurrently using `Promise.all()`.
**Incorrect (sequential execution, 3 round trips):**
```typescript
const user = await fetchUser()
const posts = await fetchPosts()
const comments = await fetchComments()
```
**Correct (parallel execution, 1 round trip):**
```typescript
const [user, posts, comments] = await Promise.all([
fetchUser(),
fetchPosts(),
fetchComments()
])
```

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---
title: Strategic Suspense Boundaries
impact: HIGH
impactDescription: faster initial paint
tags: async, suspense, streaming, layout-shift
---
## Strategic Suspense Boundaries
Instead of awaiting data in async components before returning JSX, use Suspense boundaries to show the wrapper UI faster while data loads.
**Incorrect (wrapper blocked by data fetching):**
```tsx
async function Page() {
const data = await fetchData() // Blocks entire page
return (
<div>
<div>Sidebar</div>
<div>Header</div>
<div>
<DataDisplay data={data} />
</div>
<div>Footer</div>
</div>
)
}
```
The entire layout waits for data even though only the middle section needs it.
**Correct (wrapper shows immediately, data streams in):**
```tsx
function Page() {
return (
<div>
<div>Sidebar</div>
<div>Header</div>
<div>
<Suspense fallback={<Skeleton />}>
<DataDisplay />
</Suspense>
</div>
<div>Footer</div>
</div>
)
}
async function DataDisplay() {
const data = await fetchData() // Only blocks this component
return <div>{data.content}</div>
}
```
Sidebar, Header, and Footer render immediately. Only DataDisplay waits for data.
**Alternative (share promise across components):**
```tsx
function Page() {
// Start fetch immediately, but don't await
const dataPromise = fetchData()
return (
<div>
<div>Sidebar</div>
<div>Header</div>
<Suspense fallback={<Skeleton />}>
<DataDisplay dataPromise={dataPromise} />
<DataSummary dataPromise={dataPromise} />
</Suspense>
<div>Footer</div>
</div>
)
}
function DataDisplay({ dataPromise }: { dataPromise: Promise<Data> }) {
const data = use(dataPromise) // Unwraps the promise
return <div>{data.content}</div>
}
function DataSummary({ dataPromise }: { dataPromise: Promise<Data> }) {
const data = use(dataPromise) // Reuses the same promise
return <div>{data.summary}</div>
}
```
Both components share the same promise, so only one fetch occurs. Layout renders immediately while both components wait together.
**When NOT to use this pattern:**
- Critical data needed for layout decisions (affects positioning)
- SEO-critical content above the fold
- Small, fast queries where suspense overhead isn't worth it
- When you want to avoid layout shift (loading → content jump)
**Trade-off:** Faster initial paint vs potential layout shift. Choose based on your UX priorities.

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---
title: Prefer Statically Analyzable Paths
impact: HIGH
impactDescription: avoids accidental broad bundles and file traces
tags: bundle, nextjs, vite, webpack, rollup, esbuild, path
---
## Prefer Statically Analyzable Paths
Build tools work best when import and file-system paths are obvious at build time. If you hide the real path inside a variable or compose it too dynamically, the tool either has to include a broad set of possible files, warn that it cannot analyze the import, or widen file tracing to stay safe.
Prefer explicit maps or literal paths so the set of reachable files stays narrow and predictable. This is the same rule whether you are choosing modules with `import()` or reading files in server/build code.
When analysis becomes too broad, the cost is real:
- Larger server bundles
- Slower builds
- Worse cold starts
- More memory use
### Import Paths
**Incorrect (the bundler cannot tell what may be imported):**
```ts
const PAGE_MODULES = {
home: './pages/home',
settings: './pages/settings',
} as const
const Page = await import(PAGE_MODULES[pageName])
```
**Correct (use an explicit map of allowed modules):**
```ts
const PAGE_MODULES = {
home: () => import('./pages/home'),
settings: () => import('./pages/settings'),
} as const
const Page = await PAGE_MODULES[pageName]()
```
### File-System Paths
**Incorrect (a 2-value enum still hides the final path from static analysis):**
```ts
const baseDir = path.join(process.cwd(), 'content/' + contentKind)
```
**Correct (make each final path literal at the callsite):**
```ts
const baseDir =
kind === ContentKind.Blog
? path.join(process.cwd(), 'content/blog')
: path.join(process.cwd(), 'content/docs')
```
In Next.js server code, this matters for output file tracing too. `path.join(process.cwd(), someVar)` can widen the traced file set because Next.js statically analyze `import`, `require`, and `fs` usage.
Reference: [Next.js output](https://nextjs.org/docs/app/api-reference/config/next-config-js/output), [Next.js dynamic imports](https://nextjs.org/learn/seo/dynamic-imports), [Vite features](https://vite.dev/guide/features.html), [esbuild API](https://esbuild.github.io/api/), [Rollup dynamic import vars](https://www.npmjs.com/package/@rollup/plugin-dynamic-import-vars), [Webpack dependency management](https://webpack.js.org/guides/dependency-management/)

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---
title: Avoid Barrel File Imports
impact: CRITICAL
impactDescription: 200-800ms import cost, slow builds
tags: bundle, imports, tree-shaking, barrel-files, performance
---
## Avoid Barrel File Imports
Import directly from source files instead of barrel files to avoid loading thousands of unused modules. **Barrel files** are entry points that re-export multiple modules (e.g., `index.js` that does `export * from './module'`).
Popular icon and component libraries can have **up to 10,000 re-exports** in their entry file. For many React packages, **it takes 200-800ms just to import them**, affecting both development speed and production cold starts.
**Why tree-shaking doesn't help:** When a library is marked as external (not bundled), the bundler can't optimize it. If you bundle it to enable tree-shaking, builds become substantially slower analyzing the entire module graph.
**Incorrect (imports entire library):**
```tsx
import { Check, X, Menu } from 'lucide-react'
// Loads 1,583 modules, takes ~2.8s extra in dev
// Runtime cost: 200-800ms on every cold start
import { Button, TextField } from '@mui/material'
// Loads 2,225 modules, takes ~4.2s extra in dev
```
**Correct - Next.js 13.5+ (recommended):**
```js
// next.config.js - automatically optimizes barrel imports at build time
module.exports = {
experimental: {
optimizePackageImports: ['lucide-react', '@mui/material']
}
}
```
```tsx
// Keep the standard imports - Next.js transforms them to direct imports
import { Check, X, Menu } from 'lucide-react'
// Full TypeScript support, no manual path wrangling
```
This is the recommended approach because it preserves TypeScript type safety and editor autocompletion while still eliminating the barrel import cost.
**Correct - Direct imports (non-Next.js projects):**
```tsx
import Button from '@mui/material/Button'
import TextField from '@mui/material/TextField'
// Loads only what you use
```
> **TypeScript warning:** Some libraries (notably `lucide-react`) don't ship `.d.ts` files for their deep import paths. Importing from `lucide-react/dist/esm/icons/check` resolves to an implicit `any` type, causing errors under `strict` or `noImplicitAny`. Prefer `optimizePackageImports` when available, or verify the library exports types for its subpaths before using direct imports.
These optimizations provide 15-70% faster dev boot, 28% faster builds, 40% faster cold starts, and significantly faster HMR.
Libraries commonly affected: `lucide-react`, `@mui/material`, `@mui/icons-material`, `@tabler/icons-react`, `react-icons`, `@headlessui/react`, `@radix-ui/react-*`, `lodash`, `ramda`, `date-fns`, `rxjs`, `react-use`.
Reference: [How we optimized package imports in Next.js](https://vercel.com/blog/how-we-optimized-package-imports-in-next-js)

View File

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---
title: Conditional Module Loading
impact: HIGH
impactDescription: loads large data only when needed
tags: bundle, conditional-loading, lazy-loading
---
## Conditional Module Loading
Load large data or modules only when a feature is activated.
**Example (lazy-load animation frames):**
```tsx
function AnimationPlayer({ enabled, setEnabled }: { enabled: boolean; setEnabled: React.Dispatch<React.SetStateAction<boolean>> }) {
const [frames, setFrames] = useState<Frame[] | null>(null)
useEffect(() => {
if (enabled && !frames && typeof window !== 'undefined') {
import('./animation-frames.js')
.then(mod => setFrames(mod.frames))
.catch(() => setEnabled(false))
}
}, [enabled, frames, setEnabled])
if (!frames) return <Skeleton />
return <Canvas frames={frames} />
}
```
The `typeof window !== 'undefined'` check prevents bundling this module for SSR, optimizing server bundle size and build speed.

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---
title: Defer Non-Critical Third-Party Libraries
impact: MEDIUM
impactDescription: loads after hydration
tags: bundle, third-party, analytics, defer
---
## Defer Non-Critical Third-Party Libraries
Analytics, logging, and error tracking don't block user interaction. Load them after hydration.
**Incorrect (blocks initial bundle):**
```tsx
import { Analytics } from '@vercel/analytics/react'
export default function RootLayout({ children }) {
return (
<html>
<body>
{children}
<Analytics />
</body>
</html>
)
}
```
**Correct (loads after hydration):**
```tsx
import dynamic from 'next/dynamic'
const Analytics = dynamic(
() => import('@vercel/analytics/react').then(m => m.Analytics),
{ ssr: false }
)
export default function RootLayout({ children }) {
return (
<html>
<body>
{children}
<Analytics />
</body>
</html>
)
}
```

View File

@@ -0,0 +1,35 @@
---
title: Dynamic Imports for Heavy Components
impact: CRITICAL
impactDescription: directly affects TTI and LCP
tags: bundle, dynamic-import, code-splitting, next-dynamic
---
## Dynamic Imports for Heavy Components
Use `next/dynamic` to lazy-load large components not needed on initial render.
**Incorrect (Monaco bundles with main chunk ~300KB):**
```tsx
import { MonacoEditor } from './monaco-editor'
function CodePanel({ code }: { code: string }) {
return <MonacoEditor value={code} />
}
```
**Correct (Monaco loads on demand):**
```tsx
import dynamic from 'next/dynamic'
const MonacoEditor = dynamic(
() => import('./monaco-editor').then(m => m.MonacoEditor),
{ ssr: false }
)
function CodePanel({ code }: { code: string }) {
return <MonacoEditor value={code} />
}
```

View File

@@ -0,0 +1,50 @@
---
title: Preload Based on User Intent
impact: MEDIUM
impactDescription: reduces perceived latency
tags: bundle, preload, user-intent, hover
---
## Preload Based on User Intent
Preload heavy bundles before they're needed to reduce perceived latency.
**Example (preload on hover/focus):**
```tsx
function EditorButton({ onClick }: { onClick: () => void }) {
const preload = () => {
if (typeof window !== 'undefined') {
void import('./monaco-editor')
}
}
return (
<button
onMouseEnter={preload}
onFocus={preload}
onClick={onClick}
>
Open Editor
</button>
)
}
```
**Example (preload when feature flag is enabled):**
```tsx
function FlagsProvider({ children, flags }: Props) {
useEffect(() => {
if (flags.editorEnabled && typeof window !== 'undefined') {
void import('./monaco-editor').then(mod => mod.init())
}
}, [flags.editorEnabled])
return <FlagsContext.Provider value={flags}>
{children}
</FlagsContext.Provider>
}
```
The `typeof window !== 'undefined'` check prevents bundling preloaded modules for SSR, optimizing server bundle size and build speed.

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---
title: Deduplicate Global Event Listeners
impact: LOW
impactDescription: single listener for N components
tags: client, swr, event-listeners, subscription
---
## Deduplicate Global Event Listeners
Use `useSWRSubscription()` to share global event listeners across component instances.
**Incorrect (N instances = N listeners):**
```tsx
function useKeyboardShortcut(key: string, callback: () => void) {
useEffect(() => {
const handler = (e: KeyboardEvent) => {
if (e.metaKey && e.key === key) {
callback()
}
}
window.addEventListener('keydown', handler)
return () => window.removeEventListener('keydown', handler)
}, [key, callback])
}
```
When using the `useKeyboardShortcut` hook multiple times, each instance will register a new listener.
**Correct (N instances = 1 listener):**
```tsx
import useSWRSubscription from 'swr/subscription'
// Module-level Map to track callbacks per key
const keyCallbacks = new Map<string, Set<() => void>>()
function useKeyboardShortcut(key: string, callback: () => void) {
// Register this callback in the Map
useEffect(() => {
if (!keyCallbacks.has(key)) {
keyCallbacks.set(key, new Set())
}
keyCallbacks.get(key)!.add(callback)
return () => {
const set = keyCallbacks.get(key)
if (set) {
set.delete(callback)
if (set.size === 0) {
keyCallbacks.delete(key)
}
}
}
}, [key, callback])
useSWRSubscription('global-keydown', () => {
const handler = (e: KeyboardEvent) => {
if (e.metaKey && keyCallbacks.has(e.key)) {
keyCallbacks.get(e.key)!.forEach(cb => cb())
}
}
window.addEventListener('keydown', handler)
return () => window.removeEventListener('keydown', handler)
})
}
function Profile() {
// Multiple shortcuts will share the same listener
useKeyboardShortcut('p', () => { /* ... */ })
useKeyboardShortcut('k', () => { /* ... */ })
// ...
}
```

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---
title: Version and Minimize localStorage Data
impact: MEDIUM
impactDescription: prevents schema conflicts, reduces storage size
tags: client, localStorage, storage, versioning, data-minimization
---
## Version and Minimize localStorage Data
Add version prefix to keys and store only needed fields. Prevents schema conflicts and accidental storage of sensitive data.
**Incorrect:**
```typescript
// No version, stores everything, no error handling
localStorage.setItem('userConfig', JSON.stringify(fullUserObject))
const data = localStorage.getItem('userConfig')
```
**Correct:**
```typescript
const VERSION = 'v2'
function saveConfig(config: { theme: string; language: string }) {
try {
localStorage.setItem(`userConfig:${VERSION}`, JSON.stringify(config))
} catch {
// Throws in incognito/private browsing, quota exceeded, or disabled
}
}
function loadConfig() {
try {
const data = localStorage.getItem(`userConfig:${VERSION}`)
return data ? JSON.parse(data) : null
} catch {
return null
}
}
// Migration from v1 to v2
function migrate() {
try {
const v1 = localStorage.getItem('userConfig:v1')
if (v1) {
const old = JSON.parse(v1)
saveConfig({ theme: old.darkMode ? 'dark' : 'light', language: old.lang })
localStorage.removeItem('userConfig:v1')
}
} catch {}
}
```
**Store minimal fields from server responses:**
```typescript
// User object has 20+ fields, only store what UI needs
function cachePrefs(user: FullUser) {
try {
localStorage.setItem('prefs:v1', JSON.stringify({
theme: user.preferences.theme,
notifications: user.preferences.notifications
}))
} catch {}
}
```
**Always wrap in try-catch:** `getItem()` and `setItem()` throw in incognito/private browsing (Safari, Firefox), when quota exceeded, or when disabled.
**Benefits:** Schema evolution via versioning, reduced storage size, prevents storing tokens/PII/internal flags.

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---
title: Use Passive Event Listeners for Scrolling Performance
impact: MEDIUM
impactDescription: eliminates scroll delay caused by event listeners
tags: client, event-listeners, scrolling, performance, touch, wheel
---
## Use Passive Event Listeners for Scrolling Performance
Add `{ passive: true }` to touch and wheel event listeners to enable immediate scrolling. Browsers normally wait for listeners to finish to check if `preventDefault()` is called, causing scroll delay.
**Incorrect:**
```typescript
useEffect(() => {
const handleTouch = (e: TouchEvent) => console.log(e.touches[0].clientX)
const handleWheel = (e: WheelEvent) => console.log(e.deltaY)
document.addEventListener('touchstart', handleTouch)
document.addEventListener('wheel', handleWheel)
return () => {
document.removeEventListener('touchstart', handleTouch)
document.removeEventListener('wheel', handleWheel)
}
}, [])
```
**Correct:**
```typescript
useEffect(() => {
const handleTouch = (e: TouchEvent) => console.log(e.touches[0].clientX)
const handleWheel = (e: WheelEvent) => console.log(e.deltaY)
document.addEventListener('touchstart', handleTouch, { passive: true })
document.addEventListener('wheel', handleWheel, { passive: true })
return () => {
document.removeEventListener('touchstart', handleTouch)
document.removeEventListener('wheel', handleWheel)
}
}, [])
```
**Use passive when:** tracking/analytics, logging, any listener that doesn't call `preventDefault()`.
**Don't use passive when:** implementing custom swipe gestures, custom zoom controls, or any listener that needs `preventDefault()`.

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---
title: Use SWR for Automatic Deduplication
impact: MEDIUM-HIGH
impactDescription: automatic deduplication
tags: client, swr, deduplication, data-fetching
---
## Use SWR for Automatic Deduplication
SWR enables request deduplication, caching, and revalidation across component instances.
**Incorrect (no deduplication, each instance fetches):**
```tsx
function UserList() {
const [users, setUsers] = useState([])
useEffect(() => {
fetch('/api/users')
.then(r => r.json())
.then(setUsers)
}, [])
}
```
**Correct (multiple instances share one request):**
```tsx
import useSWR from 'swr'
function UserList() {
const { data: users } = useSWR('/api/users', fetcher)
}
```
**For immutable data:**
```tsx
import { useImmutableSWR } from '@/lib/swr'
function StaticContent() {
const { data } = useImmutableSWR('/api/config', fetcher)
}
```
**For mutations:**
```tsx
import { useSWRMutation } from 'swr/mutation'
function UpdateButton() {
const { trigger } = useSWRMutation('/api/user', updateUser)
return <button onClick={() => trigger()}>Update</button>
}
```
Reference: [https://swr.vercel.app](https://swr.vercel.app)

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---
title: Avoid Layout Thrashing
impact: MEDIUM
impactDescription: prevents forced synchronous layouts and reduces performance bottlenecks
tags: javascript, dom, css, performance, reflow, layout-thrashing
---
## Avoid Layout Thrashing
Avoid interleaving style writes with layout reads. When you read a layout property (like `offsetWidth`, `getBoundingClientRect()`, or `getComputedStyle()`) between style changes, the browser is forced to trigger a synchronous reflow.
**This is OK (browser batches style changes):**
```typescript
function updateElementStyles(element: HTMLElement) {
// Each line invalidates style, but browser batches the recalculation
element.style.width = '100px'
element.style.height = '200px'
element.style.backgroundColor = 'blue'
element.style.border = '1px solid black'
}
```
**Incorrect (interleaved reads and writes force reflows):**
```typescript
function layoutThrashing(element: HTMLElement) {
element.style.width = '100px'
const width = element.offsetWidth // Forces reflow
element.style.height = '200px'
const height = element.offsetHeight // Forces another reflow
}
```
**Correct (batch writes, then read once):**
```typescript
function updateElementStyles(element: HTMLElement) {
// Batch all writes together
element.style.width = '100px'
element.style.height = '200px'
element.style.backgroundColor = 'blue'
element.style.border = '1px solid black'
// Read after all writes are done (single reflow)
const { width, height } = element.getBoundingClientRect()
}
```
**Correct (batch reads, then writes):**
```typescript
function avoidThrashing(element: HTMLElement) {
// Read phase - all layout queries first
const rect1 = element.getBoundingClientRect()
const offsetWidth = element.offsetWidth
const offsetHeight = element.offsetHeight
// Write phase - all style changes after
element.style.width = '100px'
element.style.height = '200px'
}
```
**Better: use CSS classes**
```css
.highlighted-box {
width: 100px;
height: 200px;
background-color: blue;
border: 1px solid black;
}
```
```typescript
function updateElementStyles(element: HTMLElement) {
element.classList.add('highlighted-box')
const { width, height } = element.getBoundingClientRect()
}
```
**React example:**
```tsx
// Incorrect: interleaving style changes with layout queries
function Box({ isHighlighted }: { isHighlighted: boolean }) {
const ref = useRef<HTMLDivElement>(null)
useEffect(() => {
if (ref.current && isHighlighted) {
ref.current.style.width = '100px'
const width = ref.current.offsetWidth // Forces layout
ref.current.style.height = '200px'
}
}, [isHighlighted])
return <div ref={ref}>Content</div>
}
// Correct: toggle class
function Box({ isHighlighted }: { isHighlighted: boolean }) {
return (
<div className={isHighlighted ? 'highlighted-box' : ''}>
Content
</div>
)
}
```
Prefer CSS classes over inline styles when possible. CSS files are cached by the browser, and classes provide better separation of concerns and are easier to maintain.
See [this gist](https://gist.github.com/paulirish/5d52fb081b3570c81e3a) and [CSS Triggers](https://csstriggers.com/) for more information on layout-forcing operations.

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---
title: Cache Repeated Function Calls
impact: MEDIUM
impactDescription: avoid redundant computation
tags: javascript, cache, memoization, performance
---
## Cache Repeated Function Calls
Use a module-level Map to cache function results when the same function is called repeatedly with the same inputs during render.
**Incorrect (redundant computation):**
```typescript
function ProjectList({ projects }: { projects: Project[] }) {
return (
<div>
{projects.map(project => {
// slugify() called 100+ times for same project names
const slug = slugify(project.name)
return <ProjectCard key={project.id} slug={slug} />
})}
</div>
)
}
```
**Correct (cached results):**
```typescript
// Module-level cache
const slugifyCache = new Map<string, string>()
function cachedSlugify(text: string): string {
if (slugifyCache.has(text)) {
return slugifyCache.get(text)!
}
const result = slugify(text)
slugifyCache.set(text, result)
return result
}
function ProjectList({ projects }: { projects: Project[] }) {
return (
<div>
{projects.map(project => {
// Computed only once per unique project name
const slug = cachedSlugify(project.name)
return <ProjectCard key={project.id} slug={slug} />
})}
</div>
)
}
```
**Simpler pattern for single-value functions:**
```typescript
let isLoggedInCache: boolean | null = null
function isLoggedIn(): boolean {
if (isLoggedInCache !== null) {
return isLoggedInCache
}
isLoggedInCache = document.cookie.includes('auth=')
return isLoggedInCache
}
// Clear cache when auth changes
function onAuthChange() {
isLoggedInCache = null
}
```
Use a Map (not a hook) so it works everywhere: utilities, event handlers, not just React components.
Reference: [How we made the Vercel Dashboard twice as fast](https://vercel.com/blog/how-we-made-the-vercel-dashboard-twice-as-fast)

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---
title: Cache Property Access in Loops
impact: LOW-MEDIUM
impactDescription: reduces lookups
tags: javascript, loops, optimization, caching
---
## Cache Property Access in Loops
Cache object property lookups in hot paths.
**Incorrect (3 lookups × N iterations):**
```typescript
for (let i = 0; i < arr.length; i++) {
process(obj.config.settings.value)
}
```
**Correct (1 lookup total):**
```typescript
const value = obj.config.settings.value
const len = arr.length
for (let i = 0; i < len; i++) {
process(value)
}
```

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@@ -0,0 +1,70 @@
---
title: Cache Storage API Calls
impact: LOW-MEDIUM
impactDescription: reduces expensive I/O
tags: javascript, localStorage, storage, caching, performance
---
## Cache Storage API Calls
`localStorage`, `sessionStorage`, and `document.cookie` are synchronous and expensive. Cache reads in memory.
**Incorrect (reads storage on every call):**
```typescript
function getTheme() {
return localStorage.getItem('theme') ?? 'light'
}
// Called 10 times = 10 storage reads
```
**Correct (Map cache):**
```typescript
const storageCache = new Map<string, string | null>()
function getLocalStorage(key: string) {
if (!storageCache.has(key)) {
storageCache.set(key, localStorage.getItem(key))
}
return storageCache.get(key)
}
function setLocalStorage(key: string, value: string) {
localStorage.setItem(key, value)
storageCache.set(key, value) // keep cache in sync
}
```
Use a Map (not a hook) so it works everywhere: utilities, event handlers, not just React components.
**Cookie caching:**
```typescript
let cookieCache: Record<string, string> | null = null
function getCookie(name: string) {
if (!cookieCache) {
cookieCache = Object.fromEntries(
document.cookie.split('; ').map(c => c.split('='))
)
}
return cookieCache[name]
}
```
**Important (invalidate on external changes):**
If storage can change externally (another tab, server-set cookies), invalidate cache:
```typescript
window.addEventListener('storage', (e) => {
if (e.key) storageCache.delete(e.key)
})
document.addEventListener('visibilitychange', () => {
if (document.visibilityState === 'visible') {
storageCache.clear()
}
})
```

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---
title: Combine Multiple Array Iterations
impact: LOW-MEDIUM
impactDescription: reduces iterations
tags: javascript, arrays, loops, performance
---
## Combine Multiple Array Iterations
Multiple `.filter()` or `.map()` calls iterate the array multiple times. Combine into one loop.
**Incorrect (3 iterations):**
```typescript
const admins = users.filter(u => u.isAdmin)
const testers = users.filter(u => u.isTester)
const inactive = users.filter(u => !u.isActive)
```
**Correct (1 iteration):**
```typescript
const admins: User[] = []
const testers: User[] = []
const inactive: User[] = []
for (const user of users) {
if (user.isAdmin) admins.push(user)
if (user.isTester) testers.push(user)
if (!user.isActive) inactive.push(user)
}
```

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---
title: Early Return from Functions
impact: LOW-MEDIUM
impactDescription: avoids unnecessary computation
tags: javascript, functions, optimization, early-return
---
## Early Return from Functions
Return early when result is determined to skip unnecessary processing.
**Incorrect (processes all items even after finding answer):**
```typescript
function validateUsers(users: User[]) {
let hasError = false
let errorMessage = ''
for (const user of users) {
if (!user.email) {
hasError = true
errorMessage = 'Email required'
}
if (!user.name) {
hasError = true
errorMessage = 'Name required'
}
// Continues checking all users even after error found
}
return hasError ? { valid: false, error: errorMessage } : { valid: true }
}
```
**Correct (returns immediately on first error):**
```typescript
function validateUsers(users: User[]) {
for (const user of users) {
if (!user.email) {
return { valid: false, error: 'Email required' }
}
if (!user.name) {
return { valid: false, error: 'Name required' }
}
}
return { valid: true }
}
```

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---
title: Use flatMap to Map and Filter in One Pass
impact: LOW-MEDIUM
impactDescription: eliminates intermediate array
tags: javascript, arrays, flatMap, filter, performance
---
## Use flatMap to Map and Filter in One Pass
**Impact: LOW-MEDIUM (eliminates intermediate array)**
Chaining `.map().filter(Boolean)` creates an intermediate array and iterates twice. Use `.flatMap()` to transform and filter in a single pass.
**Incorrect (2 iterations, intermediate array):**
```typescript
const userNames = users
.map(user => user.isActive ? user.name : null)
.filter(Boolean)
```
**Correct (1 iteration, no intermediate array):**
```typescript
const userNames = users.flatMap(user =>
user.isActive ? [user.name] : []
)
```
**More examples:**
```typescript
// Extract valid emails from responses
// Before
const emails = responses
.map(r => r.success ? r.data.email : null)
.filter(Boolean)
// After
const emails = responses.flatMap(r =>
r.success ? [r.data.email] : []
)
// Parse and filter valid numbers
// Before
const numbers = strings
.map(s => parseInt(s, 10))
.filter(n => !isNaN(n))
// After
const numbers = strings.flatMap(s => {
const n = parseInt(s, 10)
return isNaN(n) ? [] : [n]
})
```
**When to use:**
- Transforming items while filtering some out
- Conditional mapping where some inputs produce no output
- Parsing/validating where invalid inputs should be skipped

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---
title: Hoist RegExp Creation
impact: LOW-MEDIUM
impactDescription: avoids recreation
tags: javascript, regexp, optimization, memoization
---
## Hoist RegExp Creation
Don't create RegExp inside render. Hoist to module scope or memoize with `useMemo()`.
**Incorrect (new RegExp every render):**
```tsx
function Highlighter({ text, query }: Props) {
const regex = new RegExp(`(${query})`, 'gi')
const parts = text.split(regex)
return <>{parts.map((part, i) => ...)}</>
}
```
**Correct (memoize or hoist):**
```tsx
const EMAIL_REGEX = /^[^\s@]+@[^\s@]+\.[^\s@]+$/
function Highlighter({ text, query }: Props) {
const regex = useMemo(
() => new RegExp(`(${escapeRegex(query)})`, 'gi'),
[query]
)
const parts = text.split(regex)
return <>{parts.map((part, i) => ...)}</>
}
```
**Warning (global regex has mutable state):**
Global regex (`/g`) has mutable `lastIndex` state:
```typescript
const regex = /foo/g
regex.test('foo') // true, lastIndex = 3
regex.test('foo') // false, lastIndex = 0
```

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---
title: Build Index Maps for Repeated Lookups
impact: LOW-MEDIUM
impactDescription: 1M ops to 2K ops
tags: javascript, map, indexing, optimization, performance
---
## Build Index Maps for Repeated Lookups
Multiple `.find()` calls by the same key should use a Map.
**Incorrect (O(n) per lookup):**
```typescript
function processOrders(orders: Order[], users: User[]) {
return orders.map(order => ({
...order,
user: users.find(u => u.id === order.userId)
}))
}
```
**Correct (O(1) per lookup):**
```typescript
function processOrders(orders: Order[], users: User[]) {
const userById = new Map(users.map(u => [u.id, u]))
return orders.map(order => ({
...order,
user: userById.get(order.userId)
}))
}
```
Build map once (O(n)), then all lookups are O(1).
For 1000 orders × 1000 users: 1M ops → 2K ops.

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---
title: Early Length Check for Array Comparisons
impact: MEDIUM-HIGH
impactDescription: avoids expensive operations when lengths differ
tags: javascript, arrays, performance, optimization, comparison
---
## Early Length Check for Array Comparisons
When comparing arrays with expensive operations (sorting, deep equality, serialization), check lengths first. If lengths differ, the arrays cannot be equal.
In real-world applications, this optimization is especially valuable when the comparison runs in hot paths (event handlers, render loops).
**Incorrect (always runs expensive comparison):**
```typescript
function hasChanges(current: string[], original: string[]) {
// Always sorts and joins, even when lengths differ
return current.sort().join() !== original.sort().join()
}
```
Two O(n log n) sorts run even when `current.length` is 5 and `original.length` is 100. There is also overhead of joining the arrays and comparing the strings.
**Correct (O(1) length check first):**
```typescript
function hasChanges(current: string[], original: string[]) {
// Early return if lengths differ
if (current.length !== original.length) {
return true
}
// Only sort when lengths match
const currentSorted = current.toSorted()
const originalSorted = original.toSorted()
for (let i = 0; i < currentSorted.length; i++) {
if (currentSorted[i] !== originalSorted[i]) {
return true
}
}
return false
}
```
This new approach is more efficient because:
- It avoids the overhead of sorting and joining the arrays when lengths differ
- It avoids consuming memory for the joined strings (especially important for large arrays)
- It avoids mutating the original arrays
- It returns early when a difference is found

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---
title: Use Loop for Min/Max Instead of Sort
impact: LOW
impactDescription: O(n) instead of O(n log n)
tags: javascript, arrays, performance, sorting, algorithms
---
## Use Loop for Min/Max Instead of Sort
Finding the smallest or largest element only requires a single pass through the array. Sorting is wasteful and slower.
**Incorrect (O(n log n) - sort to find latest):**
```typescript
interface Project {
id: string
name: string
updatedAt: number
}
function getLatestProject(projects: Project[]) {
const sorted = [...projects].sort((a, b) => b.updatedAt - a.updatedAt)
return sorted[0]
}
```
Sorts the entire array just to find the maximum value.
**Incorrect (O(n log n) - sort for oldest and newest):**
```typescript
function getOldestAndNewest(projects: Project[]) {
const sorted = [...projects].sort((a, b) => a.updatedAt - b.updatedAt)
return { oldest: sorted[0], newest: sorted[sorted.length - 1] }
}
```
Still sorts unnecessarily when only min/max are needed.
**Correct (O(n) - single loop):**
```typescript
function getLatestProject(projects: Project[]) {
if (projects.length === 0) return null
let latest = projects[0]
for (let i = 1; i < projects.length; i++) {
if (projects[i].updatedAt > latest.updatedAt) {
latest = projects[i]
}
}
return latest
}
function getOldestAndNewest(projects: Project[]) {
if (projects.length === 0) return { oldest: null, newest: null }
let oldest = projects[0]
let newest = projects[0]
for (let i = 1; i < projects.length; i++) {
if (projects[i].updatedAt < oldest.updatedAt) oldest = projects[i]
if (projects[i].updatedAt > newest.updatedAt) newest = projects[i]
}
return { oldest, newest }
}
```
Single pass through the array, no copying, no sorting.
**Alternative (Math.min/Math.max for small arrays):**
```typescript
const numbers = [5, 2, 8, 1, 9]
const min = Math.min(...numbers)
const max = Math.max(...numbers)
```
This works for small arrays, but can be slower or just throw an error for very large arrays due to spread operator limitations. Maximal array length is approximately 124000 in Chrome 143 and 638000 in Safari 18; exact numbers may vary - see [the fiddle](https://jsfiddle.net/qw1jabsx/4/). Use the loop approach for reliability.

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---
title: Defer Non-Critical Work with requestIdleCallback
impact: MEDIUM
impactDescription: keeps UI responsive during background tasks
tags: javascript, performance, idle, scheduling, analytics
---
## Defer Non-Critical Work with requestIdleCallback
**Impact: MEDIUM (keeps UI responsive during background tasks)**
Use `requestIdleCallback()` to schedule non-critical work during browser idle periods. This keeps the main thread free for user interactions and animations, reducing jank and improving perceived performance.
**Incorrect (blocks main thread during user interaction):**
```typescript
function handleSearch(query: string) {
const results = searchItems(query)
setResults(results)
// These block the main thread immediately
analytics.track('search', { query })
saveToRecentSearches(query)
prefetchTopResults(results.slice(0, 3))
}
```
**Correct (defers non-critical work to idle time):**
```typescript
function handleSearch(query: string) {
const results = searchItems(query)
setResults(results)
// Defer non-critical work to idle periods
requestIdleCallback(() => {
analytics.track('search', { query })
})
requestIdleCallback(() => {
saveToRecentSearches(query)
})
requestIdleCallback(() => {
prefetchTopResults(results.slice(0, 3))
})
}
```
**With timeout for required work:**
```typescript
// Ensure analytics fires within 2 seconds even if browser stays busy
requestIdleCallback(
() => analytics.track('page_view', { path: location.pathname }),
{ timeout: 2000 }
)
```
**Chunking large tasks:**
```typescript
function processLargeDataset(items: Item[]) {
let index = 0
function processChunk(deadline: IdleDeadline) {
// Process items while we have idle time (aim for <50ms chunks)
while (index < items.length && deadline.timeRemaining() > 0) {
processItem(items[index])
index++
}
// Schedule next chunk if more items remain
if (index < items.length) {
requestIdleCallback(processChunk)
}
}
requestIdleCallback(processChunk)
}
```
**With fallback for unsupported browsers:**
```typescript
const scheduleIdleWork = window.requestIdleCallback ?? ((cb: () => void) => setTimeout(cb, 1))
scheduleIdleWork(() => {
// Non-critical work
})
```
**When to use:**
- Analytics and telemetry
- Saving state to localStorage/IndexedDB
- Prefetching resources for likely next actions
- Processing non-urgent data transformations
- Lazy initialization of non-critical features
**When NOT to use:**
- User-initiated actions that need immediate feedback
- Rendering updates the user is waiting for
- Time-sensitive operations

View File

@@ -0,0 +1,24 @@
---
title: Use Set/Map for O(1) Lookups
impact: LOW-MEDIUM
impactDescription: O(n) to O(1)
tags: javascript, set, map, data-structures, performance
---
## Use Set/Map for O(1) Lookups
Convert arrays to Set/Map for repeated membership checks.
**Incorrect (O(n) per check):**
```typescript
const allowedIds = ['a', 'b', 'c', ...]
items.filter(item => allowedIds.includes(item.id))
```
**Correct (O(1) per check):**
```typescript
const allowedIds = new Set(['a', 'b', 'c', ...])
items.filter(item => allowedIds.has(item.id))
```

View File

@@ -0,0 +1,57 @@
---
title: Use toSorted() Instead of sort() for Immutability
impact: MEDIUM-HIGH
impactDescription: prevents mutation bugs in React state
tags: javascript, arrays, immutability, react, state, mutation
---
## Use toSorted() Instead of sort() for Immutability
`.sort()` mutates the array in place, which can cause bugs with React state and props. Use `.toSorted()` to create a new sorted array without mutation.
**Incorrect (mutates original array):**
```typescript
function UserList({ users }: { users: User[] }) {
// Mutates the users prop array!
const sorted = useMemo(
() => users.sort((a, b) => a.name.localeCompare(b.name)),
[users]
)
return <div>{sorted.map(renderUser)}</div>
}
```
**Correct (creates new array):**
```typescript
function UserList({ users }: { users: User[] }) {
// Creates new sorted array, original unchanged
const sorted = useMemo(
() => users.toSorted((a, b) => a.name.localeCompare(b.name)),
[users]
)
return <div>{sorted.map(renderUser)}</div>
}
```
**Why this matters in React:**
1. Props/state mutations break React's immutability model - React expects props and state to be treated as read-only
2. Causes stale closure bugs - Mutating arrays inside closures (callbacks, effects) can lead to unexpected behavior
**Browser support (fallback for older browsers):**
`.toSorted()` is available in all modern browsers (Chrome 110+, Safari 16+, Firefox 115+, Node.js 20+). For older environments, use spread operator:
```typescript
// Fallback for older browsers
const sorted = [...items].sort((a, b) => a.value - b.value)
```
**Other immutable array methods:**
- `.toSorted()` - immutable sort
- `.toReversed()` - immutable reverse
- `.toSpliced()` - immutable splice
- `.with()` - immutable element replacement

View File

@@ -0,0 +1,26 @@
---
title: Use Activity Component for Show/Hide
impact: MEDIUM
impactDescription: preserves state/DOM
tags: rendering, activity, visibility, state-preservation
---
## Use Activity Component for Show/Hide
Use React's `<Activity>` to preserve state/DOM for expensive components that frequently toggle visibility.
**Usage:**
```tsx
import { Activity } from 'react'
function Dropdown({ isOpen }: Props) {
return (
<Activity mode={isOpen ? 'visible' : 'hidden'}>
<ExpensiveMenu />
</Activity>
)
}
```
Avoids expensive re-renders and state loss.

View File

@@ -0,0 +1,47 @@
---
title: Animate SVG Wrapper Instead of SVG Element
impact: LOW
impactDescription: enables hardware acceleration
tags: rendering, svg, css, animation, performance
---
## Animate SVG Wrapper Instead of SVG Element
Many browsers don't have hardware acceleration for CSS3 animations on SVG elements. Wrap SVG in a `<div>` and animate the wrapper instead.
**Incorrect (animating SVG directly - no hardware acceleration):**
```tsx
function LoadingSpinner() {
return (
<svg
className="animate-spin"
width="24"
height="24"
viewBox="0 0 24 24"
>
<circle cx="12" cy="12" r="10" stroke="currentColor" />
</svg>
)
}
```
**Correct (animating wrapper div - hardware accelerated):**
```tsx
function LoadingSpinner() {
return (
<div className="animate-spin">
<svg
width="24"
height="24"
viewBox="0 0 24 24"
>
<circle cx="12" cy="12" r="10" stroke="currentColor" />
</svg>
</div>
)
}
```
This applies to all CSS transforms and transitions (`transform`, `opacity`, `translate`, `scale`, `rotate`). The wrapper div allows browsers to use GPU acceleration for smoother animations.

View File

@@ -0,0 +1,40 @@
---
title: Use Explicit Conditional Rendering
impact: LOW
impactDescription: prevents rendering 0 or NaN
tags: rendering, conditional, jsx, falsy-values
---
## Use Explicit Conditional Rendering
Use explicit ternary operators (`? :`) instead of `&&` for conditional rendering when the condition can be `0`, `NaN`, or other falsy values that render.
**Incorrect (renders "0" when count is 0):**
```tsx
function Badge({ count }: { count: number }) {
return (
<div>
{count && <span className="badge">{count}</span>}
</div>
)
}
// When count = 0, renders: <div>0</div>
// When count = 5, renders: <div><span class="badge">5</span></div>
```
**Correct (renders nothing when count is 0):**
```tsx
function Badge({ count }: { count: number }) {
return (
<div>
{count > 0 ? <span className="badge">{count}</span> : null}
</div>
)
}
// When count = 0, renders: <div></div>
// When count = 5, renders: <div><span class="badge">5</span></div>
```

View File

@@ -0,0 +1,38 @@
---
title: CSS content-visibility for Long Lists
impact: HIGH
impactDescription: faster initial render
tags: rendering, css, content-visibility, long-lists
---
## CSS content-visibility for Long Lists
Apply `content-visibility: auto` to defer off-screen rendering.
**CSS:**
```css
.message-item {
content-visibility: auto;
contain-intrinsic-size: 0 80px;
}
```
**Example:**
```tsx
function MessageList({ messages }: { messages: Message[] }) {
return (
<div className="overflow-y-auto h-screen">
{messages.map(msg => (
<div key={msg.id} className="message-item">
<Avatar user={msg.author} />
<div>{msg.content}</div>
</div>
))}
</div>
)
}
```
For 1000 messages, browser skips layout/paint for ~990 off-screen items (10× faster initial render).

View File

@@ -0,0 +1,46 @@
---
title: Hoist Static JSX Elements
impact: LOW
impactDescription: avoids re-creation
tags: rendering, jsx, static, optimization
---
## Hoist Static JSX Elements
Extract static JSX outside components to avoid re-creation.
**Incorrect (recreates element every render):**
```tsx
function LoadingSkeleton() {
return <div className="animate-pulse h-20 bg-gray-200" />
}
function Container() {
return (
<div>
{loading && <LoadingSkeleton />}
</div>
)
}
```
**Correct (reuses same element):**
```tsx
const loadingSkeleton = (
<div className="animate-pulse h-20 bg-gray-200" />
)
function Container() {
return (
<div>
{loading && loadingSkeleton}
</div>
)
}
```
This is especially helpful for large and static SVG nodes, which can be expensive to recreate on every render.
**Note:** If your project has [React Compiler](https://react.dev/learn/react-compiler) enabled, the compiler automatically hoists static JSX elements and optimizes component re-renders, making manual hoisting unnecessary.

View File

@@ -0,0 +1,82 @@
---
title: Prevent Hydration Mismatch Without Flickering
impact: MEDIUM
impactDescription: avoids visual flicker and hydration errors
tags: rendering, ssr, hydration, localStorage, flicker
---
## Prevent Hydration Mismatch Without Flickering
When rendering content that depends on client-side storage (localStorage, cookies), avoid both SSR breakage and post-hydration flickering by injecting a synchronous script that updates the DOM before React hydrates.
**Incorrect (breaks SSR):**
```tsx
function ThemeWrapper({ children }: { children: ReactNode }) {
// localStorage is not available on server - throws error
const theme = localStorage.getItem('theme') || 'light'
return (
<div className={theme}>
{children}
</div>
)
}
```
Server-side rendering will fail because `localStorage` is undefined.
**Incorrect (visual flickering):**
```tsx
function ThemeWrapper({ children }: { children: ReactNode }) {
const [theme, setTheme] = useState('light')
useEffect(() => {
// Runs after hydration - causes visible flash
const stored = localStorage.getItem('theme')
if (stored) {
setTheme(stored)
}
}, [])
return (
<div className={theme}>
{children}
</div>
)
}
```
Component first renders with default value (`light`), then updates after hydration, causing a visible flash of incorrect content.
**Correct (no flicker, no hydration mismatch):**
```tsx
function ThemeWrapper({ children }: { children: ReactNode }) {
return (
<>
<div id="theme-wrapper">
{children}
</div>
<script
dangerouslySetInnerHTML={{
__html: `
(function() {
try {
var theme = localStorage.getItem('theme') || 'light';
var el = document.getElementById('theme-wrapper');
if (el) el.className = theme;
} catch (e) {}
})();
`,
}}
/>
</>
)
}
```
The inline script executes synchronously before showing the element, ensuring the DOM already has the correct value. No flickering, no hydration mismatch.
This pattern is especially useful for theme toggles, user preferences, authentication states, and any client-only data that should render immediately without flashing default values.

View File

@@ -0,0 +1,30 @@
---
title: Suppress Expected Hydration Mismatches
impact: LOW-MEDIUM
impactDescription: avoids noisy hydration warnings for known differences
tags: rendering, hydration, ssr, nextjs
---
## Suppress Expected Hydration Mismatches
In SSR frameworks (e.g., Next.js), some values are intentionally different on server vs client (random IDs, dates, locale/timezone formatting). For these *expected* mismatches, wrap the dynamic text in an element with `suppressHydrationWarning` to prevent noisy warnings. Do not use this to hide real bugs. Dont overuse it.
**Incorrect (known mismatch warnings):**
```tsx
function Timestamp() {
return <span>{new Date().toLocaleString()}</span>
}
```
**Correct (suppress expected mismatch only):**
```tsx
function Timestamp() {
return (
<span suppressHydrationWarning>
{new Date().toLocaleString()}
</span>
)
}
```

View File

@@ -0,0 +1,85 @@
---
title: Use React DOM Resource Hints
impact: HIGH
impactDescription: reduces load time for critical resources
tags: rendering, preload, preconnect, prefetch, resource-hints
---
## Use React DOM Resource Hints
**Impact: HIGH (reduces load time for critical resources)**
React DOM provides APIs to hint the browser about resources it will need. These are especially useful in server components to start loading resources before the client even receives the HTML.
- **`prefetchDNS(href)`**: Resolve DNS for a domain you expect to connect to
- **`preconnect(href)`**: Establish connection (DNS + TCP + TLS) to a server
- **`preload(href, options)`**: Fetch a resource (stylesheet, font, script, image) you'll use soon
- **`preloadModule(href)`**: Fetch an ES module you'll use soon
- **`preinit(href, options)`**: Fetch and evaluate a stylesheet or script
- **`preinitModule(href)`**: Fetch and evaluate an ES module
**Example (preconnect to third-party APIs):**
```tsx
import { preconnect, prefetchDNS } from 'react-dom'
export default function App() {
prefetchDNS('https://analytics.example.com')
preconnect('https://api.example.com')
return <main>{/* content */}</main>
}
```
**Example (preload critical fonts and styles):**
```tsx
import { preload, preinit } from 'react-dom'
export default function RootLayout({ children }) {
// Preload font file
preload('/fonts/inter.woff2', { as: 'font', type: 'font/woff2', crossOrigin: 'anonymous' })
// Fetch and apply critical stylesheet immediately
preinit('/styles/critical.css', { as: 'style' })
return (
<html>
<body>{children}</body>
</html>
)
}
```
**Example (preload modules for code-split routes):**
```tsx
import { preloadModule, preinitModule } from 'react-dom'
function Navigation() {
const preloadDashboard = () => {
preloadModule('/dashboard.js', { as: 'script' })
}
return (
<nav>
<a href="/dashboard" onMouseEnter={preloadDashboard}>
Dashboard
</a>
</nav>
)
}
```
**When to use each:**
| API | Use case |
|-----|----------|
| `prefetchDNS` | Third-party domains you'll connect to later |
| `preconnect` | APIs or CDNs you'll fetch from immediately |
| `preload` | Critical resources needed for current page |
| `preloadModule` | JS modules for likely next navigation |
| `preinit` | Stylesheets/scripts that must execute early |
| `preinitModule` | ES modules that must execute early |
Reference: [React DOM Resource Preloading APIs](https://react.dev/reference/react-dom#resource-preloading-apis)

View File

@@ -0,0 +1,68 @@
---
title: Use defer or async on Script Tags
impact: HIGH
impactDescription: eliminates render-blocking
tags: rendering, script, defer, async, performance
---
## Use defer or async on Script Tags
**Impact: HIGH (eliminates render-blocking)**
Script tags without `defer` or `async` block HTML parsing while the script downloads and executes. This delays First Contentful Paint and Time to Interactive.
- **`defer`**: Downloads in parallel, executes after HTML parsing completes, maintains execution order
- **`async`**: Downloads in parallel, executes immediately when ready, no guaranteed order
Use `defer` for scripts that depend on DOM or other scripts. Use `async` for independent scripts like analytics.
**Incorrect (blocks rendering):**
```tsx
export default function Document() {
return (
<html>
<head>
<script src="https://example.com/analytics.js" />
<script src="/scripts/utils.js" />
</head>
<body>{/* content */}</body>
</html>
)
}
```
**Correct (non-blocking):**
```tsx
export default function Document() {
return (
<html>
<head>
{/* Independent script - use async */}
<script src="https://example.com/analytics.js" async />
{/* DOM-dependent script - use defer */}
<script src="/scripts/utils.js" defer />
</head>
<body>{/* content */}</body>
</html>
)
}
```
**Note:** In Next.js, prefer the `next/script` component with `strategy` prop instead of raw script tags:
```tsx
import Script from 'next/script'
export default function Page() {
return (
<>
<Script src="https://example.com/analytics.js" strategy="afterInteractive" />
<Script src="/scripts/utils.js" strategy="beforeInteractive" />
</>
)
}
```
Reference: [MDN - Script element](https://developer.mozilla.org/en-US/docs/Web/HTML/Element/script#defer)

View File

@@ -0,0 +1,28 @@
---
title: Optimize SVG Precision
impact: LOW
impactDescription: reduces file size
tags: rendering, svg, optimization, svgo
---
## Optimize SVG Precision
Reduce SVG coordinate precision to decrease file size. The optimal precision depends on the viewBox size, but in general reducing precision should be considered.
**Incorrect (excessive precision):**
```svg
<path d="M 10.293847 20.847362 L 30.938472 40.192837" />
```
**Correct (1 decimal place):**
```svg
<path d="M 10.3 20.8 L 30.9 40.2" />
```
**Automate with SVGO:**
```bash
npx svgo --precision=1 --multipass icon.svg
```

View File

@@ -0,0 +1,75 @@
---
title: Use useTransition Over Manual Loading States
impact: LOW
impactDescription: reduces re-renders and improves code clarity
tags: rendering, transitions, useTransition, loading, state
---
## Use useTransition Over Manual Loading States
Use `useTransition` instead of manual `useState` for loading states. This provides built-in `isPending` state and automatically manages transitions.
**Incorrect (manual loading state):**
```tsx
function SearchResults() {
const [query, setQuery] = useState('')
const [results, setResults] = useState([])
const [isLoading, setIsLoading] = useState(false)
const handleSearch = async (value: string) => {
setIsLoading(true)
setQuery(value)
const data = await fetchResults(value)
setResults(data)
setIsLoading(false)
}
return (
<>
<input onChange={(e) => handleSearch(e.target.value)} />
{isLoading && <Spinner />}
<ResultsList results={results} />
</>
)
}
```
**Correct (useTransition with built-in pending state):**
```tsx
import { useTransition, useState } from 'react'
function SearchResults() {
const [query, setQuery] = useState('')
const [results, setResults] = useState([])
const [isPending, startTransition] = useTransition()
const handleSearch = (value: string) => {
setQuery(value) // Update input immediately
startTransition(async () => {
// Fetch and update results
const data = await fetchResults(value)
setResults(data)
})
}
return (
<>
<input onChange={(e) => handleSearch(e.target.value)} />
{isPending && <Spinner />}
<ResultsList results={results} />
</>
)
}
```
**Benefits:**
- **Automatic pending state**: No need to manually manage `setIsLoading(true/false)`
- **Error resilience**: Pending state correctly resets even if the transition throws
- **Better responsiveness**: Keeps the UI responsive during updates
- **Interrupt handling**: New transitions automatically cancel pending ones
Reference: [useTransition](https://react.dev/reference/react/useTransition)

View File

@@ -0,0 +1,39 @@
---
title: Defer State Reads to Usage Point
impact: MEDIUM
impactDescription: avoids unnecessary subscriptions
tags: rerender, searchParams, localStorage, optimization
---
## Defer State Reads to Usage Point
Don't subscribe to dynamic state (searchParams, localStorage) if you only read it inside callbacks.
**Incorrect (subscribes to all searchParams changes):**
```tsx
function ShareButton({ chatId }: { chatId: string }) {
const searchParams = useSearchParams()
const handleShare = () => {
const ref = searchParams.get('ref')
shareChat(chatId, { ref })
}
return <button onClick={handleShare}>Share</button>
}
```
**Correct (reads on demand, no subscription):**
```tsx
function ShareButton({ chatId }: { chatId: string }) {
const handleShare = () => {
const params = new URLSearchParams(window.location.search)
const ref = params.get('ref')
shareChat(chatId, { ref })
}
return <button onClick={handleShare}>Share</button>
}
```

View File

@@ -0,0 +1,45 @@
---
title: Narrow Effect Dependencies
impact: LOW
impactDescription: minimizes effect re-runs
tags: rerender, useEffect, dependencies, optimization
---
## Narrow Effect Dependencies
Specify primitive dependencies instead of objects to minimize effect re-runs.
**Incorrect (re-runs on any user field change):**
```tsx
useEffect(() => {
console.log(user.id)
}, [user])
```
**Correct (re-runs only when id changes):**
```tsx
useEffect(() => {
console.log(user.id)
}, [user.id])
```
**For derived state, compute outside effect:**
```tsx
// Incorrect: runs on width=767, 766, 765...
useEffect(() => {
if (width < 768) {
enableMobileMode()
}
}, [width])
// Correct: runs only on boolean transition
const isMobile = width < 768
useEffect(() => {
if (isMobile) {
enableMobileMode()
}
}, [isMobile])
```

View File

@@ -0,0 +1,40 @@
---
title: Calculate Derived State During Rendering
impact: MEDIUM
impactDescription: avoids redundant renders and state drift
tags: rerender, derived-state, useEffect, state
---
## Calculate Derived State During Rendering
If a value can be computed from current props/state, do not store it in state or update it in an effect. Derive it during render to avoid extra renders and state drift. Do not set state in effects solely in response to prop changes; prefer derived values or keyed resets instead.
**Incorrect (redundant state and effect):**
```tsx
function Form() {
const [firstName, setFirstName] = useState('First')
const [lastName, setLastName] = useState('Last')
const [fullName, setFullName] = useState('')
useEffect(() => {
setFullName(firstName + ' ' + lastName)
}, [firstName, lastName])
return <p>{fullName}</p>
}
```
**Correct (derive during render):**
```tsx
function Form() {
const [firstName, setFirstName] = useState('First')
const [lastName, setLastName] = useState('Last')
const fullName = firstName + ' ' + lastName
return <p>{fullName}</p>
}
```
References: [You Might Not Need an Effect](https://react.dev/learn/you-might-not-need-an-effect)

View File

@@ -0,0 +1,29 @@
---
title: Subscribe to Derived State
impact: MEDIUM
impactDescription: reduces re-render frequency
tags: rerender, derived-state, media-query, optimization
---
## Subscribe to Derived State
Subscribe to derived boolean state instead of continuous values to reduce re-render frequency.
**Incorrect (re-renders on every pixel change):**
```tsx
function Sidebar() {
const width = useWindowWidth() // updates continuously
const isMobile = width < 768
return <nav className={isMobile ? 'mobile' : 'desktop'} />
}
```
**Correct (re-renders only when boolean changes):**
```tsx
function Sidebar() {
const isMobile = useMediaQuery('(max-width: 767px)')
return <nav className={isMobile ? 'mobile' : 'desktop'} />
}
```

View File

@@ -0,0 +1,74 @@
---
title: Use Functional setState Updates
impact: MEDIUM
impactDescription: prevents stale closures and unnecessary callback recreations
tags: react, hooks, useState, useCallback, callbacks, closures
---
## Use Functional setState Updates
When updating state based on the current state value, use the functional update form of setState instead of directly referencing the state variable. This prevents stale closures, eliminates unnecessary dependencies, and creates stable callback references.
**Incorrect (requires state as dependency):**
```tsx
function TodoList() {
const [items, setItems] = useState(initialItems)
// Callback must depend on items, recreated on every items change
const addItems = useCallback((newItems: Item[]) => {
setItems([...items, ...newItems])
}, [items]) // ❌ items dependency causes recreations
// Risk of stale closure if dependency is forgotten
const removeItem = useCallback((id: string) => {
setItems(items.filter(item => item.id !== id))
}, []) // ❌ Missing items dependency - will use stale items!
return <ItemsEditor items={items} onAdd={addItems} onRemove={removeItem} />
}
```
The first callback is recreated every time `items` changes, which can cause child components to re-render unnecessarily. The second callback has a stale closure bug—it will always reference the initial `items` value.
**Correct (stable callbacks, no stale closures):**
```tsx
function TodoList() {
const [items, setItems] = useState(initialItems)
// Stable callback, never recreated
const addItems = useCallback((newItems: Item[]) => {
setItems(curr => [...curr, ...newItems])
}, []) // ✅ No dependencies needed
// Always uses latest state, no stale closure risk
const removeItem = useCallback((id: string) => {
setItems(curr => curr.filter(item => item.id !== id))
}, []) // ✅ Safe and stable
return <ItemsEditor items={items} onAdd={addItems} onRemove={removeItem} />
}
```
**Benefits:**
1. **Stable callback references** - Callbacks don't need to be recreated when state changes
2. **No stale closures** - Always operates on the latest state value
3. **Fewer dependencies** - Simplifies dependency arrays and reduces memory leaks
4. **Prevents bugs** - Eliminates the most common source of React closure bugs
**When to use functional updates:**
- Any setState that depends on the current state value
- Inside useCallback/useMemo when state is needed
- Event handlers that reference state
- Async operations that update state
**When direct updates are fine:**
- Setting state to a static value: `setCount(0)`
- Setting state from props/arguments only: `setName(newName)`
- State doesn't depend on previous value
**Note:** If your project has [React Compiler](https://react.dev/learn/react-compiler) enabled, the compiler can automatically optimize some cases, but functional updates are still recommended for correctness and to prevent stale closure bugs.

View File

@@ -0,0 +1,58 @@
---
title: Use Lazy State Initialization
impact: MEDIUM
impactDescription: wasted computation on every render
tags: react, hooks, useState, performance, initialization
---
## Use Lazy State Initialization
Pass a function to `useState` for expensive initial values. Without the function form, the initializer runs on every render even though the value is only used once.
**Incorrect (runs on every render):**
```tsx
function FilteredList({ items }: { items: Item[] }) {
// buildSearchIndex() runs on EVERY render, even after initialization
const [searchIndex, setSearchIndex] = useState(buildSearchIndex(items))
const [query, setQuery] = useState('')
// When query changes, buildSearchIndex runs again unnecessarily
return <SearchResults index={searchIndex} query={query} />
}
function UserProfile() {
// JSON.parse runs on every render
const [settings, setSettings] = useState(
JSON.parse(localStorage.getItem('settings') || '{}')
)
return <SettingsForm settings={settings} onChange={setSettings} />
}
```
**Correct (runs only once):**
```tsx
function FilteredList({ items }: { items: Item[] }) {
// buildSearchIndex() runs ONLY on initial render
const [searchIndex, setSearchIndex] = useState(() => buildSearchIndex(items))
const [query, setQuery] = useState('')
return <SearchResults index={searchIndex} query={query} />
}
function UserProfile() {
// JSON.parse runs only on initial render
const [settings, setSettings] = useState(() => {
const stored = localStorage.getItem('settings')
return stored ? JSON.parse(stored) : {}
})
return <SettingsForm settings={settings} onChange={setSettings} />
}
```
Use lazy initialization when computing initial values from localStorage/sessionStorage, building data structures (indexes, maps), reading from the DOM, or performing heavy transformations.
For simple primitives (`useState(0)`), direct references (`useState(props.value)`), or cheap literals (`useState({})`), the function form is unnecessary.

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@@ -0,0 +1,38 @@
---
title: Extract Default Non-primitive Parameter Value from Memoized Component to Constant
impact: MEDIUM
impactDescription: restores memoization by using a constant for default value
tags: rerender, memo, optimization
---
## Extract Default Non-primitive Parameter Value from Memoized Component to Constant
When memoized component has a default value for some non-primitive optional parameter, such as an array, function, or object, calling the component without that parameter results in broken memoization. This is because new value instances are created on every rerender, and they do not pass strict equality comparison in `memo()`.
To address this issue, extract the default value into a constant.
**Incorrect (`onClick` has different values on every rerender):**
```tsx
const UserAvatar = memo(function UserAvatar({ onClick = () => {} }: { onClick?: () => void }) {
// ...
})
// Used without optional onClick
<UserAvatar />
```
**Correct (stable default value):**
```tsx
const NOOP = () => {};
const UserAvatar = memo(function UserAvatar({ onClick = NOOP }: { onClick?: () => void }) {
// ...
})
// Used without optional onClick
<UserAvatar />
```

View File

@@ -0,0 +1,44 @@
---
title: Extract to Memoized Components
impact: MEDIUM
impactDescription: enables early returns
tags: rerender, memo, useMemo, optimization
---
## Extract to Memoized Components
Extract expensive work into memoized components to enable early returns before computation.
**Incorrect (computes avatar even when loading):**
```tsx
function Profile({ user, loading }: Props) {
const avatar = useMemo(() => {
const id = computeAvatarId(user)
return <Avatar id={id} />
}, [user])
if (loading) return <Skeleton />
return <div>{avatar}</div>
}
```
**Correct (skips computation when loading):**
```tsx
const UserAvatar = memo(function UserAvatar({ user }: { user: User }) {
const id = useMemo(() => computeAvatarId(user), [user])
return <Avatar id={id} />
})
function Profile({ user, loading }: Props) {
if (loading) return <Skeleton />
return (
<div>
<UserAvatar user={user} />
</div>
)
}
```
**Note:** If your project has [React Compiler](https://react.dev/learn/react-compiler) enabled, manual memoization with `memo()` and `useMemo()` is not necessary. The compiler automatically optimizes re-renders.

View File

@@ -0,0 +1,45 @@
---
title: Put Interaction Logic in Event Handlers
impact: MEDIUM
impactDescription: avoids effect re-runs and duplicate side effects
tags: rerender, useEffect, events, side-effects, dependencies
---
## Put Interaction Logic in Event Handlers
If a side effect is triggered by a specific user action (submit, click, drag), run it in that event handler. Do not model the action as state + effect; it makes effects re-run on unrelated changes and can duplicate the action.
**Incorrect (event modeled as state + effect):**
```tsx
function Form() {
const [submitted, setSubmitted] = useState(false)
const theme = useContext(ThemeContext)
useEffect(() => {
if (submitted) {
post('/api/register')
showToast('Registered', theme)
}
}, [submitted, theme])
return <button onClick={() => setSubmitted(true)}>Submit</button>
}
```
**Correct (do it in the handler):**
```tsx
function Form() {
const theme = useContext(ThemeContext)
function handleSubmit() {
post('/api/register')
showToast('Registered', theme)
}
return <button onClick={handleSubmit}>Submit</button>
}
```
Reference: [Should this code move to an event handler?](https://react.dev/learn/removing-effect-dependencies#should-this-code-move-to-an-event-handler)

View File

@@ -0,0 +1,82 @@
---
title: Don't Define Components Inside Components
impact: HIGH
impactDescription: prevents remount on every render
tags: rerender, components, remount, performance
---
## Don't Define Components Inside Components
**Impact: HIGH (prevents remount on every render)**
Defining a component inside another component creates a new component type on every render. React sees a different component each time and fully remounts it, destroying all state and DOM.
A common reason developers do this is to access parent variables without passing props. Always pass props instead.
**Incorrect (remounts on every render):**
```tsx
function UserProfile({ user, theme }) {
// Defined inside to access `theme` - BAD
const Avatar = () => (
<img
src={user.avatarUrl}
className={theme === 'dark' ? 'avatar-dark' : 'avatar-light'}
/>
)
// Defined inside to access `user` - BAD
const Stats = () => (
<div>
<span>{user.followers} followers</span>
<span>{user.posts} posts</span>
</div>
)
return (
<div>
<Avatar />
<Stats />
</div>
)
}
```
Every time `UserProfile` renders, `Avatar` and `Stats` are new component types. React unmounts the old instances and mounts new ones, losing any internal state, running effects again, and recreating DOM nodes.
**Correct (pass props instead):**
```tsx
function Avatar({ src, theme }: { src: string; theme: string }) {
return (
<img
src={src}
className={theme === 'dark' ? 'avatar-dark' : 'avatar-light'}
/>
)
}
function Stats({ followers, posts }: { followers: number; posts: number }) {
return (
<div>
<span>{followers} followers</span>
<span>{posts} posts</span>
</div>
)
}
function UserProfile({ user, theme }) {
return (
<div>
<Avatar src={user.avatarUrl} theme={theme} />
<Stats followers={user.followers} posts={user.posts} />
</div>
)
}
```
**Symptoms of this bug:**
- Input fields lose focus on every keystroke
- Animations restart unexpectedly
- `useEffect` cleanup/setup runs on every parent render
- Scroll position resets inside the component

View File

@@ -0,0 +1,35 @@
---
title: Do not wrap a simple expression with a primitive result type in useMemo
impact: LOW-MEDIUM
impactDescription: wasted computation on every render
tags: rerender, useMemo, optimization
---
## Do not wrap a simple expression with a primitive result type in useMemo
When an expression is simple (few logical or arithmetical operators) and has a primitive result type (boolean, number, string), do not wrap it in `useMemo`.
Calling `useMemo` and comparing hook dependencies may consume more resources than the expression itself.
**Incorrect:**
```tsx
function Header({ user, notifications }: Props) {
const isLoading = useMemo(() => {
return user.isLoading || notifications.isLoading
}, [user.isLoading, notifications.isLoading])
if (isLoading) return <Skeleton />
// return some markup
}
```
**Correct:**
```tsx
function Header({ user, notifications }: Props) {
const isLoading = user.isLoading || notifications.isLoading
if (isLoading) return <Skeleton />
// return some markup
}
```

View File

@@ -0,0 +1,64 @@
---
title: Split Combined Hook Computations
impact: MEDIUM
impactDescription: avoids recomputing independent steps
tags: rerender, useMemo, useEffect, dependencies, optimization
---
## Split Combined Hook Computations
When a hook contains multiple independent tasks with different dependencies, split them into separate hooks. A combined hook reruns all tasks when any dependency changes, even if some tasks don't use the changed value.
**Incorrect (changing `sortOrder` recomputes filtering):**
```tsx
const sortedProducts = useMemo(() => {
const filtered = products.filter((p) => p.category === category)
const sorted = filtered.toSorted((a, b) =>
sortOrder === "asc" ? a.price - b.price : b.price - a.price
)
return sorted
}, [products, category, sortOrder])
```
**Correct (filtering only recomputes when products or category change):**
```tsx
const filteredProducts = useMemo(
() => products.filter((p) => p.category === category),
[products, category]
)
const sortedProducts = useMemo(
() =>
filteredProducts.toSorted((a, b) =>
sortOrder === "asc" ? a.price - b.price : b.price - a.price
),
[filteredProducts, sortOrder]
)
```
This pattern also applies to `useEffect` when combining unrelated side effects:
**Incorrect (both effects run when either dependency changes):**
```tsx
useEffect(() => {
analytics.trackPageView(pathname)
document.title = `${pageTitle} | My App`
}, [pathname, pageTitle])
```
**Correct (effects run independently):**
```tsx
useEffect(() => {
analytics.trackPageView(pathname)
}, [pathname])
useEffect(() => {
document.title = `${pageTitle} | My App`
}, [pageTitle])
```
**Note:** If your project has [React Compiler](https://react.dev/learn/react-compiler) enabled, it automatically optimizes dependency tracking and may handle some of these cases for you.

View File

@@ -0,0 +1,40 @@
---
title: Use Transitions for Non-Urgent Updates
impact: MEDIUM
impactDescription: maintains UI responsiveness
tags: rerender, transitions, startTransition, performance
---
## Use Transitions for Non-Urgent Updates
Mark frequent, non-urgent state updates as transitions to maintain UI responsiveness.
**Incorrect (blocks UI on every scroll):**
```tsx
function ScrollTracker() {
const [scrollY, setScrollY] = useState(0)
useEffect(() => {
const handler = () => setScrollY(window.scrollY)
window.addEventListener('scroll', handler, { passive: true })
return () => window.removeEventListener('scroll', handler)
}, [])
}
```
**Correct (non-blocking updates):**
```tsx
import { startTransition } from 'react'
function ScrollTracker() {
const [scrollY, setScrollY] = useState(0)
useEffect(() => {
const handler = () => {
startTransition(() => setScrollY(window.scrollY))
}
window.addEventListener('scroll', handler, { passive: true })
return () => window.removeEventListener('scroll', handler)
}, [])
}
```

View File

@@ -0,0 +1,59 @@
---
title: Use useDeferredValue for Expensive Derived Renders
impact: MEDIUM
impactDescription: keeps input responsive during heavy computation
tags: rerender, useDeferredValue, optimization, concurrent
---
## Use useDeferredValue for Expensive Derived Renders
When user input triggers expensive computations or renders, use `useDeferredValue` to keep the input responsive. The deferred value lags behind, allowing React to prioritize the input update and render the expensive result when idle.
**Incorrect (input feels laggy while filtering):**
```tsx
function Search({ items }: { items: Item[] }) {
const [query, setQuery] = useState('')
const filtered = items.filter(item => fuzzyMatch(item, query))
return (
<>
<input value={query} onChange={e => setQuery(e.target.value)} />
<ResultsList results={filtered} />
</>
)
}
```
**Correct (input stays snappy, results render when ready):**
```tsx
function Search({ items }: { items: Item[] }) {
const [query, setQuery] = useState('')
const deferredQuery = useDeferredValue(query)
const filtered = useMemo(
() => items.filter(item => fuzzyMatch(item, deferredQuery)),
[items, deferredQuery]
)
const isStale = query !== deferredQuery
return (
<>
<input value={query} onChange={e => setQuery(e.target.value)} />
<div style={{ opacity: isStale ? 0.7 : 1 }}>
<ResultsList results={filtered} />
</div>
</>
)
}
```
**When to use:**
- Filtering/searching large lists
- Expensive visualizations (charts, graphs) reacting to input
- Any derived state that causes noticeable render delays
**Note:** Wrap the expensive computation in `useMemo` with the deferred value as a dependency, otherwise it still runs on every render.
Reference: [React useDeferredValue](https://react.dev/reference/react/useDeferredValue)

View File

@@ -0,0 +1,73 @@
---
title: Use useRef for Transient Values
impact: MEDIUM
impactDescription: avoids unnecessary re-renders on frequent updates
tags: rerender, useref, state, performance
---
## Use useRef for Transient Values
When a value changes frequently and you don't want a re-render on every update (e.g., mouse trackers, intervals, transient flags), store it in `useRef` instead of `useState`. Keep component state for UI; use refs for temporary DOM-adjacent values. Updating a ref does not trigger a re-render.
**Incorrect (renders every update):**
```tsx
function Tracker() {
const [lastX, setLastX] = useState(0)
useEffect(() => {
const onMove = (e: MouseEvent) => setLastX(e.clientX)
window.addEventListener('mousemove', onMove)
return () => window.removeEventListener('mousemove', onMove)
}, [])
return (
<div
style={{
position: 'fixed',
top: 0,
left: lastX,
width: 8,
height: 8,
background: 'black',
}}
/>
)
}
```
**Correct (no re-render for tracking):**
```tsx
function Tracker() {
const lastXRef = useRef(0)
const dotRef = useRef<HTMLDivElement>(null)
useEffect(() => {
const onMove = (e: MouseEvent) => {
lastXRef.current = e.clientX
const node = dotRef.current
if (node) {
node.style.transform = `translateX(${e.clientX}px)`
}
}
window.addEventListener('mousemove', onMove)
return () => window.removeEventListener('mousemove', onMove)
}, [])
return (
<div
ref={dotRef}
style={{
position: 'fixed',
top: 0,
left: 0,
width: 8,
height: 8,
background: 'black',
transform: 'translateX(0px)',
}}
/>
)
}
```

View File

@@ -0,0 +1,73 @@
---
title: Use after() for Non-Blocking Operations
impact: MEDIUM
impactDescription: faster response times
tags: server, async, logging, analytics, side-effects
---
## Use after() for Non-Blocking Operations
Use Next.js's `after()` to schedule work that should execute after a response is sent. This prevents logging, analytics, and other side effects from blocking the response.
**Incorrect (blocks response):**
```tsx
import { logUserAction } from '@/app/utils'
export async function POST(request: Request) {
// Perform mutation
await updateDatabase(request)
// Logging blocks the response
const userAgent = request.headers.get('user-agent') || 'unknown'
await logUserAction({ userAgent })
return new Response(JSON.stringify({ status: 'success' }), {
status: 200,
headers: { 'Content-Type': 'application/json' }
})
}
```
**Correct (non-blocking):**
```tsx
import { after } from 'next/server'
import { headers, cookies } from 'next/headers'
import { logUserAction } from '@/app/utils'
export async function POST(request: Request) {
// Perform mutation
await updateDatabase(request)
// Log after response is sent
after(async () => {
const userAgent = (await headers()).get('user-agent') || 'unknown'
const sessionCookie = (await cookies()).get('session-id')?.value || 'anonymous'
logUserAction({ sessionCookie, userAgent })
})
return new Response(JSON.stringify({ status: 'success' }), {
status: 200,
headers: { 'Content-Type': 'application/json' }
})
}
```
The response is sent immediately while logging happens in the background.
**Common use cases:**
- Analytics tracking
- Audit logging
- Sending notifications
- Cache invalidation
- Cleanup tasks
**Important notes:**
- `after()` runs even if the response fails or redirects
- Works in Server Actions, Route Handlers, and Server Components
Reference: [https://nextjs.org/docs/app/api-reference/functions/after](https://nextjs.org/docs/app/api-reference/functions/after)

View File

@@ -0,0 +1,96 @@
---
title: Authenticate Server Actions Like API Routes
impact: CRITICAL
impactDescription: prevents unauthorized access to server mutations
tags: server, server-actions, authentication, security, authorization
---
## Authenticate Server Actions Like API Routes
**Impact: CRITICAL (prevents unauthorized access to server mutations)**
Server Actions (functions with `"use server"`) are exposed as public endpoints, just like API routes. Always verify authentication and authorization **inside** each Server Action—do not rely solely on middleware, layout guards, or page-level checks, as Server Actions can be invoked directly.
Next.js documentation explicitly states: "Treat Server Actions with the same security considerations as public-facing API endpoints, and verify if the user is allowed to perform a mutation."
**Incorrect (no authentication check):**
```typescript
'use server'
export async function deleteUser(userId: string) {
// Anyone can call this! No auth check
await db.user.delete({ where: { id: userId } })
return { success: true }
}
```
**Correct (authentication inside the action):**
```typescript
'use server'
import { verifySession } from '@/lib/auth'
import { unauthorized } from '@/lib/errors'
export async function deleteUser(userId: string) {
// Always check auth inside the action
const session = await verifySession()
if (!session) {
throw unauthorized('Must be logged in')
}
// Check authorization too
if (session.user.role !== 'admin' && session.user.id !== userId) {
throw unauthorized('Cannot delete other users')
}
await db.user.delete({ where: { id: userId } })
return { success: true }
}
```
**With input validation:**
```typescript
'use server'
import { verifySession } from '@/lib/auth'
import { z } from 'zod'
const updateProfileSchema = z.object({
userId: z.string().uuid(),
name: z.string().min(1).max(100),
email: z.string().email()
})
export async function updateProfile(data: unknown) {
// Validate input first
const validated = updateProfileSchema.parse(data)
// Then authenticate
const session = await verifySession()
if (!session) {
throw new Error('Unauthorized')
}
// Then authorize
if (session.user.id !== validated.userId) {
throw new Error('Can only update own profile')
}
// Finally perform the mutation
await db.user.update({
where: { id: validated.userId },
data: {
name: validated.name,
email: validated.email
}
})
return { success: true }
}
```
Reference: [https://nextjs.org/docs/app/guides/authentication](https://nextjs.org/docs/app/guides/authentication)

View File

@@ -0,0 +1,41 @@
---
title: Cross-Request LRU Caching
impact: HIGH
impactDescription: caches across requests
tags: server, cache, lru, cross-request
---
## Cross-Request LRU Caching
`React.cache()` only works within one request. For data shared across sequential requests (user clicks button A then button B), use an LRU cache.
**Implementation:**
```typescript
import { LRUCache } from 'lru-cache'
const cache = new LRUCache<string, any>({
max: 1000,
ttl: 5 * 60 * 1000 // 5 minutes
})
export async function getUser(id: string) {
const cached = cache.get(id)
if (cached) return cached
const user = await db.user.findUnique({ where: { id } })
cache.set(id, user)
return user
}
// Request 1: DB query, result cached
// Request 2: cache hit, no DB query
```
Use when sequential user actions hit multiple endpoints needing the same data within seconds.
**With Vercel's [Fluid Compute](https://vercel.com/docs/fluid-compute):** LRU caching is especially effective because multiple concurrent requests can share the same function instance and cache. This means the cache persists across requests without needing external storage like Redis.
**In traditional serverless:** Each invocation runs in isolation, so consider Redis for cross-process caching.
Reference: [https://github.com/isaacs/node-lru-cache](https://github.com/isaacs/node-lru-cache)

View File

@@ -0,0 +1,76 @@
---
title: Per-Request Deduplication with React.cache()
impact: MEDIUM
impactDescription: deduplicates within request
tags: server, cache, react-cache, deduplication
---
## Per-Request Deduplication with React.cache()
Use `React.cache()` for server-side request deduplication. Authentication and database queries benefit most.
**Usage:**
```typescript
import { cache } from 'react'
export const getCurrentUser = cache(async () => {
const session = await auth()
if (!session?.user?.id) return null
return await db.user.findUnique({
where: { id: session.user.id }
})
})
```
Within a single request, multiple calls to `getCurrentUser()` execute the query only once.
**Avoid inline objects as arguments:**
`React.cache()` uses shallow equality (`Object.is`) to determine cache hits. Inline objects create new references each call, preventing cache hits.
**Incorrect (always cache miss):**
```typescript
const getUser = cache(async (params: { uid: number }) => {
return await db.user.findUnique({ where: { id: params.uid } })
})
// Each call creates new object, never hits cache
getUser({ uid: 1 })
getUser({ uid: 1 }) // Cache miss, runs query again
```
**Correct (cache hit):**
```typescript
const getUser = cache(async (uid: number) => {
return await db.user.findUnique({ where: { id: uid } })
})
// Primitive args use value equality
getUser(1)
getUser(1) // Cache hit, returns cached result
```
If you must pass objects, pass the same reference:
```typescript
const params = { uid: 1 }
getUser(params) // Query runs
getUser(params) // Cache hit (same reference)
```
**Next.js-Specific Note:**
In Next.js, the `fetch` API is automatically extended with request memoization. Requests with the same URL and options are automatically deduplicated within a single request, so you don't need `React.cache()` for `fetch` calls. However, `React.cache()` is still essential for other async tasks:
- Database queries (Prisma, Drizzle, etc.)
- Heavy computations
- Authentication checks
- File system operations
- Any non-fetch async work
Use `React.cache()` to deduplicate these operations across your component tree.
Reference: [React.cache documentation](https://react.dev/reference/react/cache)

View File

@@ -0,0 +1,65 @@
---
title: Avoid Duplicate Serialization in RSC Props
impact: LOW
impactDescription: reduces network payload by avoiding duplicate serialization
tags: server, rsc, serialization, props, client-components
---
## Avoid Duplicate Serialization in RSC Props
**Impact: LOW (reduces network payload by avoiding duplicate serialization)**
RSC→client serialization deduplicates by object reference, not value. Same reference = serialized once; new reference = serialized again. Do transformations (`.toSorted()`, `.filter()`, `.map()`) in client, not server.
**Incorrect (duplicates array):**
```tsx
// RSC: sends 6 strings (2 arrays × 3 items)
<ClientList usernames={usernames} usernamesOrdered={usernames.toSorted()} />
```
**Correct (sends 3 strings):**
```tsx
// RSC: send once
<ClientList usernames={usernames} />
// Client: transform there
'use client'
const sorted = useMemo(() => [...usernames].sort(), [usernames])
```
**Nested deduplication behavior:**
Deduplication works recursively. Impact varies by data type:
- `string[]`, `number[]`, `boolean[]`: **HIGH impact** - array + all primitives fully duplicated
- `object[]`: **LOW impact** - array duplicated, but nested objects deduplicated by reference
```tsx
// string[] - duplicates everything
usernames={['a','b']} sorted={usernames.toSorted()} // sends 4 strings
// object[] - duplicates array structure only
users={[{id:1},{id:2}]} sorted={users.toSorted()} // sends 2 arrays + 2 unique objects (not 4)
```
**Operations breaking deduplication (create new references):**
- Arrays: `.toSorted()`, `.filter()`, `.map()`, `.slice()`, `[...arr]`
- Objects: `{...obj}`, `Object.assign()`, `structuredClone()`, `JSON.parse(JSON.stringify())`
**More examples:**
```tsx
// ❌ Bad
<C users={users} active={users.filter(u => u.active)} />
<C product={product} productName={product.name} />
// ✅ Good
<C users={users} />
<C product={product} />
// Do filtering/destructuring in client
```
**Exception:** Pass derived data when transformation is expensive or client doesn't need original.

View File

@@ -0,0 +1,149 @@
---
title: Hoist Static I/O to Module Level
impact: HIGH
impactDescription: avoids repeated file/network I/O per request
tags: server, io, performance, next.js, route-handlers, og-image
---
## Hoist Static I/O to Module Level
**Impact: HIGH (avoids repeated file/network I/O per request)**
When loading static assets (fonts, logos, images, config files) in route handlers or server functions, hoist the I/O operation to module level. Module-level code runs once when the module is first imported, not on every request. This eliminates redundant file system reads or network fetches that would otherwise run on every invocation.
**Incorrect (reads font file on every request):**
```typescript
// app/api/og/route.tsx
import { ImageResponse } from 'next/og'
export async function GET(request: Request) {
// Runs on EVERY request - expensive!
const fontData = await fetch(
new URL('./fonts/Inter.ttf', import.meta.url)
).then(res => res.arrayBuffer())
const logoData = await fetch(
new URL('./images/logo.png', import.meta.url)
).then(res => res.arrayBuffer())
return new ImageResponse(
<div style={{ fontFamily: 'Inter' }}>
<img src={logoData} />
Hello World
</div>,
{ fonts: [{ name: 'Inter', data: fontData }] }
)
}
```
**Correct (loads once at module initialization):**
```typescript
// app/api/og/route.tsx
import { ImageResponse } from 'next/og'
// Module-level: runs ONCE when module is first imported
const fontData = fetch(
new URL('./fonts/Inter.ttf', import.meta.url)
).then(res => res.arrayBuffer())
const logoData = fetch(
new URL('./images/logo.png', import.meta.url)
).then(res => res.arrayBuffer())
export async function GET(request: Request) {
// Await the already-started promises
const [font, logo] = await Promise.all([fontData, logoData])
return new ImageResponse(
<div style={{ fontFamily: 'Inter' }}>
<img src={logo} />
Hello World
</div>,
{ fonts: [{ name: 'Inter', data: font }] }
)
}
```
**Correct (synchronous fs at module level):**
```typescript
// app/api/og/route.tsx
import { ImageResponse } from 'next/og'
import { readFileSync } from 'fs'
import { join } from 'path'
// Synchronous read at module level - blocks only during module init
const fontData = readFileSync(
join(process.cwd(), 'public/fonts/Inter.ttf')
)
const logoData = readFileSync(
join(process.cwd(), 'public/images/logo.png')
)
export async function GET(request: Request) {
return new ImageResponse(
<div style={{ fontFamily: 'Inter' }}>
<img src={logoData} />
Hello World
</div>,
{ fonts: [{ name: 'Inter', data: fontData }] }
)
}
```
**Incorrect (reads config on every call):**
```typescript
import fs from 'node:fs/promises'
export async function processRequest(data: Data) {
const config = JSON.parse(
await fs.readFile('./config.json', 'utf-8')
)
const template = await fs.readFile('./template.html', 'utf-8')
return render(template, data, config)
}
```
**Correct (hoists config and template to module level):**
```typescript
import fs from 'node:fs/promises'
const configPromise = fs
.readFile('./config.json', 'utf-8')
.then(JSON.parse)
const templatePromise = fs.readFile('./template.html', 'utf-8')
export async function processRequest(data: Data) {
const [config, template] = await Promise.all([
configPromise,
templatePromise,
])
return render(template, data, config)
}
```
When to use this pattern:
- Loading fonts for OG image generation
- Loading static logos, icons, or watermarks
- Reading configuration files that don't change at runtime
- Loading email templates or other static templates
- Any static asset that's the same across all requests
When not to use this pattern:
- Assets that vary per request or user
- Files that may change during runtime (use caching with TTL instead)
- Large files that would consume too much memory if kept loaded
- Sensitive data that shouldn't persist in memory
With Vercel's [Fluid Compute](https://vercel.com/docs/fluid-compute), module-level caching is especially effective because multiple concurrent requests share the same function instance. The static assets stay loaded in memory across requests without cold start penalties.
In traditional serverless, each cold start re-executes module-level code, but subsequent warm invocations reuse the loaded assets until the instance is recycled.

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---
title: Avoid Shared Module State for Request Data
impact: HIGH
impactDescription: prevents concurrency bugs and request data leaks
tags: server, rsc, ssr, concurrency, security, state
---
## Avoid Shared Module State for Request Data
For React Server Components and client components rendered during SSR, avoid using mutable module-level variables to share request-scoped data. Server renders can run concurrently in the same process. If one render writes to shared module state and another render reads it, you can get race conditions, cross-request contamination, and security bugs where one user's data appears in another user's response.
Treat module scope on the server as process-wide shared memory, not request-local state.
**Incorrect (request data leaks across concurrent renders):**
```tsx
let currentUser: User | null = null
export default async function Page() {
currentUser = await auth()
return <Dashboard />
}
async function Dashboard() {
return <div>{currentUser?.name}</div>
}
```
If two requests overlap, request A can set `currentUser`, then request B overwrites it before request A finishes rendering `Dashboard`.
**Correct (keep request data local to the render tree):**
```tsx
export default async function Page() {
const user = await auth()
return <Dashboard user={user} />
}
function Dashboard({ user }: { user: User | null }) {
return <div>{user?.name}</div>
}
```
Safe exceptions:
- Immutable static assets or config loaded once at module scope
- Shared caches intentionally designed for cross-request reuse and keyed correctly
- Process-wide singletons that do not store request- or user-specific mutable data
For static assets and config, see [Hoist Static I/O to Module Level](./server-hoist-static-io.md).

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---
title: Parallel Data Fetching with Component Composition
impact: CRITICAL
impactDescription: eliminates server-side waterfalls
tags: server, rsc, parallel-fetching, composition
---
## Parallel Data Fetching with Component Composition
React Server Components execute sequentially within a tree. Restructure with composition to parallelize data fetching.
**Incorrect (Sidebar waits for Page's fetch to complete):**
```tsx
export default async function Page() {
const header = await fetchHeader()
return (
<div>
<div>{header}</div>
<Sidebar />
</div>
)
}
async function Sidebar() {
const items = await fetchSidebarItems()
return <nav>{items.map(renderItem)}</nav>
}
```
**Correct (both fetch simultaneously):**
```tsx
async function Header() {
const data = await fetchHeader()
return <div>{data}</div>
}
async function Sidebar() {
const items = await fetchSidebarItems()
return <nav>{items.map(renderItem)}</nav>
}
export default function Page() {
return (
<div>
<Header />
<Sidebar />
</div>
)
}
```
**Alternative with children prop:**
```tsx
async function Header() {
const data = await fetchHeader()
return <div>{data}</div>
}
async function Sidebar() {
const items = await fetchSidebarItems()
return <nav>{items.map(renderItem)}</nav>
}
function Layout({ children }: { children: ReactNode }) {
return (
<div>
<Header />
{children}
</div>
)
}
export default function Page() {
return (
<Layout>
<Sidebar />
</Layout>
)
}
```

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---
title: Parallel Nested Data Fetching
impact: CRITICAL
impactDescription: eliminates server-side waterfalls
tags: server, rsc, parallel-fetching, promise-chaining
---
## Parallel Nested Data Fetching
When fetching nested data in parallel, chain dependent fetches within each item's promise so a slow item doesn't block the rest.
**Incorrect (a single slow item blocks all nested fetches):**
```tsx
const chats = await Promise.all(
chatIds.map(id => getChat(id))
)
const chatAuthors = await Promise.all(
chats.map(chat => getUser(chat.author))
)
```
If one `getChat(id)` out of 100 is extremely slow, the authors of the other 99 chats can't start loading even though their data is ready.
**Correct (each item chains its own nested fetch):**
```tsx
const chatAuthors = await Promise.all(
chatIds.map(id => getChat(id).then(chat => getUser(chat.author)))
)
```
Each item independently chains `getChat``getUser`, so a slow chat doesn't block author fetches for the others.

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---
title: Minimize Serialization at RSC Boundaries
impact: HIGH
impactDescription: reduces data transfer size
tags: server, rsc, serialization, props
---
## Minimize Serialization at RSC Boundaries
The React Server/Client boundary serializes all object properties into strings and embeds them in the HTML response and subsequent RSC requests. This serialized data directly impacts page weight and load time, so **size matters a lot**. Only pass fields that the client actually uses.
**Incorrect (serializes all 50 fields):**
```tsx
async function Page() {
const user = await fetchUser() // 50 fields
return <Profile user={user} />
}
'use client'
function Profile({ user }: { user: User }) {
return <div>{user.name}</div> // uses 1 field
}
```
**Correct (serializes only 1 field):**
```tsx
async function Page() {
const user = await fetchUser()
return <Profile name={user.name} />
}
'use client'
function Profile({ name }: { name: string }) {
return <div>{name}</div>
}
```

File diff suppressed because it is too large Load Diff

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# React Native Guidelines
A structured repository for creating and maintaining React Native Best Practices
optimized for agents and LLMs.
## Structure
- `rules/` - Individual rule files (one per rule)
- `_sections.md` - Section metadata (titles, impacts, descriptions)
- `_template.md` - Template for creating new rules
- `area-description.md` - Individual rule files
- `metadata.json` - Document metadata (version, organization, abstract)
- **`AGENTS.md`** - Compiled output (generated)
## Rules
### Core Rendering (CRITICAL)
- `rendering-text-in-text-component.md` - Wrap strings in Text components
- `rendering-no-falsy-and.md` - Avoid falsy && operator in JSX
### List Performance (HIGH)
- `list-performance-virtualize.md` - Use virtualized lists (LegendList,
FlashList)
- `list-performance-function-references.md` - Keep stable object references
- `list-performance-callbacks.md` - Hoist callbacks to list root
- `list-performance-inline-objects.md` - Avoid inline objects in renderItem
- `list-performance-item-memo.md` - Pass primitives for memoization
- `list-performance-item-expensive.md` - Keep list items lightweight
- `list-performance-images.md` - Use compressed images in lists
- `list-performance-item-types.md` - Use item types for heterogeneous lists
### Animation (HIGH)
- `animation-gpu-properties.md` - Animate transform/opacity instead of layout
- `animation-gesture-detector-press.md` - Use GestureDetector for press
animations
- `animation-derived-value.md` - Prefer useDerivedValue over useAnimatedReaction
### Scroll Performance (HIGH)
- `scroll-position-no-state.md` - Never track scroll in useState
### Navigation (HIGH)
- `navigation-native-navigators.md` - Use native stack and native tabs
### React State (MEDIUM)
- `react-state-dispatcher.md` - Use functional setState updates
- `react-state-fallback.md` - State should represent user intent only
- `react-state-minimize.md` - Minimize state variables, derive values
### State Architecture (MEDIUM)
- `state-ground-truth.md` - State must represent ground truth
### React Compiler (MEDIUM)
- `react-compiler-destructure-functions.md` - Destructure functions early
- `react-compiler-reanimated-shared-values.md` - Use .get()/.set() for shared
values
### User Interface (MEDIUM)
- `ui-expo-image.md` - Use expo-image for optimized images
- `ui-image-gallery.md` - Use Galeria for lightbox/galleries
- `ui-menus.md` - Native dropdown and context menus with Zeego
- `ui-native-modals.md` - Use native Modal with formSheet
- `ui-pressable.md` - Use Pressable instead of TouchableOpacity
- `ui-measure-views.md` - Measuring view dimensions
- `ui-safe-area-scroll.md` - Use contentInsetAdjustmentBehavior
- `ui-scrollview-content-inset.md` - Use contentInset for dynamic spacing
- `ui-styling.md` - Modern styling patterns (gap, boxShadow, gradients)
### Design System (MEDIUM)
- `design-system-compound-components.md` - Use compound components
### Monorepo (LOW)
- `monorepo-native-deps-in-app.md` - Install native deps in app directory
- `monorepo-single-dependency-versions.md` - Single dependency versions
### Third-Party Dependencies (LOW)
- `imports-design-system-folder.md` - Import from design system folder
### JavaScript (LOW)
- `js-hoist-intl.md` - Hoist Intl formatter creation
### Fonts (LOW)
- `fonts-config-plugin.md` - Load fonts natively at build time
## Creating a New Rule
1. Copy `rules/_template.md` to `rules/area-description.md`
2. Choose the appropriate area prefix:
- `rendering-` for Core Rendering
- `list-performance-` for List Performance
- `animation-` for Animation
- `scroll-` for Scroll Performance
- `navigation-` for Navigation
- `react-state-` for React State
- `state-` for State Architecture
- `react-compiler-` for React Compiler
- `ui-` for User Interface
- `design-system-` for Design System
- `monorepo-` for Monorepo
- `imports-` for Third-Party Dependencies
- `js-` for JavaScript
- `fonts-` for Fonts
3. Fill in the frontmatter and content
4. Ensure you have clear examples with explanations
## Rule File Structure
Each rule file should follow this structure:
````markdown
---
title: Rule Title Here
impact: MEDIUM
impactDescription: Optional description
tags: tag1, tag2, tag3
---
## Rule Title Here
Brief explanation of the rule and why it matters.
**Incorrect (description of what's wrong):**
```tsx
// Bad code example
```
````
**Correct (description of what's right):**
```tsx
// Good code example
```
Reference: [Link](https://example.com)
```
## File Naming Convention
- Files starting with `_` are special (excluded from build)
- Rule files: `area-description.md` (e.g., `animation-gpu-properties.md`)
- Section is automatically inferred from filename prefix
- Rules are sorted alphabetically by title within each section
## Impact Levels
- `CRITICAL` - Highest priority, causes crashes or broken UI
- `HIGH` - Significant performance improvements
- `MEDIUM` - Moderate performance improvements
- `LOW` - Incremental improvements
```

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---
name: vercel-react-native-skills
description:
React Native and Expo best practices for building performant mobile apps. Use
when building React Native components, optimizing list performance,
implementing animations, or working with native modules. Triggers on tasks
involving React Native, Expo, mobile performance, or native platform APIs.
license: MIT
metadata:
author: vercel
version: '1.0.0'
---
# React Native Skills
Comprehensive best practices for React Native and Expo applications. Contains
rules across multiple categories covering performance, animations, UI patterns,
and platform-specific optimizations.
## When to Apply
Reference these guidelines when:
- Building React Native or Expo apps
- Optimizing list and scroll performance
- Implementing animations with Reanimated
- Working with images and media
- Configuring native modules or fonts
- Structuring monorepo projects with native dependencies
## Rule Categories by Priority
| Priority | Category | Impact | Prefix |
| -------- | ---------------- | -------- | -------------------- |
| 1 | List Performance | CRITICAL | `list-performance-` |
| 2 | Animation | HIGH | `animation-` |
| 3 | Navigation | HIGH | `navigation-` |
| 4 | UI Patterns | HIGH | `ui-` |
| 5 | State Management | MEDIUM | `react-state-` |
| 6 | Rendering | MEDIUM | `rendering-` |
| 7 | Monorepo | MEDIUM | `monorepo-` |
| 8 | Configuration | LOW | `fonts-`, `imports-` |
## Quick Reference
### 1. List Performance (CRITICAL)
- `list-performance-virtualize` - Use FlashList for large lists
- `list-performance-item-memo` - Memoize list item components
- `list-performance-callbacks` - Stabilize callback references
- `list-performance-inline-objects` - Avoid inline style objects
- `list-performance-function-references` - Extract functions outside render
- `list-performance-images` - Optimize images in lists
- `list-performance-item-expensive` - Move expensive work outside items
- `list-performance-item-types` - Use item types for heterogeneous lists
### 2. Animation (HIGH)
- `animation-gpu-properties` - Animate only transform and opacity
- `animation-derived-value` - Use useDerivedValue for computed animations
- `animation-gesture-detector-press` - Use Gesture.Tap instead of Pressable
### 3. Navigation (HIGH)
- `navigation-native-navigators` - Use native stack and native tabs over JS navigators
### 4. UI Patterns (HIGH)
- `ui-expo-image` - Use expo-image for all images
- `ui-image-gallery` - Use Galeria for image lightboxes
- `ui-pressable` - Use Pressable over TouchableOpacity
- `ui-safe-area-scroll` - Handle safe areas in ScrollViews
- `ui-scrollview-content-inset` - Use contentInset for headers
- `ui-menus` - Use native context menus
- `ui-native-modals` - Use native modals when possible
- `ui-measure-views` - Use onLayout, not measure()
- `ui-styling` - Use StyleSheet.create or Nativewind
### 5. State Management (MEDIUM)
- `react-state-minimize` - Minimize state subscriptions
- `react-state-dispatcher` - Use dispatcher pattern for callbacks
- `react-state-fallback` - Show fallback on first render
- `react-compiler-destructure-functions` - Destructure for React Compiler
- `react-compiler-reanimated-shared-values` - Handle shared values with compiler
### 6. Rendering (MEDIUM)
- `rendering-text-in-text-component` - Wrap text in Text components
- `rendering-no-falsy-and` - Avoid falsy && for conditional rendering
### 7. Monorepo (MEDIUM)
- `monorepo-native-deps-in-app` - Keep native dependencies in app package
- `monorepo-single-dependency-versions` - Use single versions across packages
### 8. Configuration (LOW)
- `fonts-config-plugin` - Use config plugins for custom fonts
- `imports-design-system-folder` - Organize design system imports
- `js-hoist-intl` - Hoist Intl object creation
## How to Use
Read individual rule files for detailed explanations and code examples:
```
rules/list-performance-virtualize.md
rules/animation-gpu-properties.md
```
Each rule file contains:
- Brief explanation of why it matters
- Incorrect code example with explanation
- Correct code example with explanation
- Additional context and references
## Full Compiled Document
For the complete guide with all rules expanded: `AGENTS.md`

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{
"version": "1.0.0",
"organization": "Engineering",
"date": "January 2026",
"abstract": "Comprehensive performance optimization guide for React Native applications, designed for AI agents and LLMs. Contains 35+ rules across 13 categories, prioritized by impact from critical (core rendering, list performance) to incremental (fonts, imports). Each rule includes detailed explanations, real-world examples comparing incorrect vs. correct implementations, and specific impact metrics to guide automated refactoring and code generation.",
"references": [
"https://react.dev",
"https://reactnative.dev",
"https://docs.swmansion.com/react-native-reanimated",
"https://docs.swmansion.com/react-native-gesture-handler",
"https://docs.expo.dev",
"https://legendapp.com/open-source/legend-list",
"https://github.com/nandorojo/galeria",
"https://zeego.dev"
]
}

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# Sections
This file defines all sections, their ordering, impact levels, and descriptions.
The section ID (in parentheses) is the filename prefix used to group rules.
---
## 1. Core Rendering (rendering)
**Impact:** CRITICAL
**Description:** Fundamental React Native rendering rules. Violations cause
runtime crashes or broken UI.
## 2. List Performance (list-performance)
**Impact:** HIGH
**Description:** Optimizing virtualized lists (FlatList, LegendList, FlashList)
for smooth scrolling and fast updates.
## 3. Animation (animation)
**Impact:** HIGH
**Description:** GPU-accelerated animations, Reanimated patterns, and avoiding
render thrashing during gestures.
## 4. Scroll Performance (scroll)
**Impact:** HIGH
**Description:** Tracking scroll position without causing render thrashing.
## 5. Navigation (navigation)
**Impact:** HIGH
**Description:** Using native navigators for stack and tab navigation instead of
JS-based alternatives.
## 6. React State (react-state)
**Impact:** MEDIUM
**Description:** Patterns for managing React state to avoid stale closures and
unnecessary re-renders.
## 7. State Architecture (state)
**Impact:** MEDIUM
**Description:** Ground truth principles for state variables and derived values.
## 8. React Compiler (react-compiler)
**Impact:** MEDIUM
**Description:** Compatibility patterns for React Compiler with React Native and
Reanimated.
## 9. User Interface (ui)
**Impact:** MEDIUM
**Description:** Native UI patterns for images, menus, modals, styling, and
platform-consistent interfaces.
## 10. Design System (design-system)
**Impact:** MEDIUM
**Description:** Architecture patterns for building maintainable component
libraries.
## 11. Monorepo (monorepo)
**Impact:** LOW
**Description:** Dependency management and native module configuration in
monorepos.
## 12. Third-Party Dependencies (imports)
**Impact:** LOW
**Description:** Wrapping and re-exporting third-party dependencies for
maintainability.
## 13. JavaScript (js)
**Impact:** LOW
**Description:** Micro-optimizations like hoisting expensive object creation.
## 14. Fonts (fonts)
**Impact:** LOW
**Description:** Native font loading for improved performance.

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---
title: Rule Title Here
impact: MEDIUM
impactDescription: Optional description of impact (e.g., "20-50% improvement")
tags: tag1, tag2
---
## Rule Title Here
**Impact: MEDIUM (optional impact description)**
Brief explanation of the rule and why it matters. This should be clear and concise, explaining the performance implications.
**Incorrect (description of what's wrong):**
```typescript
// Bad code example here
const bad = example()
```
**Correct (description of what's right):**
```typescript
// Good code example here
const good = example()
```
Reference: [Link to documentation or resource](https://example.com)

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---
title: Prefer useDerivedValue Over useAnimatedReaction
impact: MEDIUM
impactDescription: cleaner code, automatic dependency tracking
tags: animation, reanimated, derived-value
---
## Prefer useDerivedValue Over useAnimatedReaction
When deriving a shared value from another, use `useDerivedValue` instead of
`useAnimatedReaction`. Derived values are declarative, automatically track
dependencies, and return a value you can use directly. Animated reactions are
for side effects, not derivations.
**Incorrect (useAnimatedReaction for derivation):**
```tsx
import { useSharedValue, useAnimatedReaction } from 'react-native-reanimated'
function MyComponent() {
const progress = useSharedValue(0)
const opacity = useSharedValue(1)
useAnimatedReaction(
() => progress.value,
(current) => {
opacity.value = 1 - current
}
)
// ...
}
```
**Correct (useDerivedValue):**
```tsx
import { useSharedValue, useDerivedValue } from 'react-native-reanimated'
function MyComponent() {
const progress = useSharedValue(0)
const opacity = useDerivedValue(() => 1 - progress.get())
// ...
}
```
Use `useAnimatedReaction` only for side effects that don't produce a value
(e.g., triggering haptics, logging, calling `runOnJS`).
Reference:
[Reanimated useDerivedValue](https://docs.swmansion.com/react-native-reanimated/docs/core/useDerivedValue)

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---
title: Use GestureDetector for Animated Press States
impact: MEDIUM
impactDescription: UI thread animations, smoother press feedback
tags: animation, gestures, press, reanimated
---
## Use GestureDetector for Animated Press States
For animated press states (scale, opacity on press), use `GestureDetector` with
`Gesture.Tap()` and shared values instead of Pressable's
`onPressIn`/`onPressOut`. Gesture callbacks run on the UI thread as worklets—no
JS thread round-trip for press animations.
**Incorrect (Pressable with JS thread callbacks):**
```tsx
import { Pressable } from 'react-native'
import Animated, {
useSharedValue,
useAnimatedStyle,
withTiming,
} from 'react-native-reanimated'
function AnimatedButton({ onPress }: { onPress: () => void }) {
const scale = useSharedValue(1)
const animatedStyle = useAnimatedStyle(() => ({
transform: [{ scale: scale.value }],
}))
return (
<Pressable
onPress={onPress}
onPressIn={() => (scale.value = withTiming(0.95))}
onPressOut={() => (scale.value = withTiming(1))}
>
<Animated.View style={animatedStyle}>
<Text>Press me</Text>
</Animated.View>
</Pressable>
)
}
```
**Correct (GestureDetector with UI thread worklets):**
```tsx
import { Gesture, GestureDetector } from 'react-native-gesture-handler'
import Animated, {
useSharedValue,
useAnimatedStyle,
withTiming,
interpolate,
runOnJS,
} from 'react-native-reanimated'
function AnimatedButton({ onPress }: { onPress: () => void }) {
// Store the press STATE (0 = not pressed, 1 = pressed)
const pressed = useSharedValue(0)
const tap = Gesture.Tap()
.onBegin(() => {
pressed.set(withTiming(1))
})
.onFinalize(() => {
pressed.set(withTiming(0))
})
.onEnd(() => {
runOnJS(onPress)()
})
// Derive visual values from the state
const animatedStyle = useAnimatedStyle(() => ({
transform: [
{ scale: interpolate(withTiming(pressed.get()), [0, 1], [1, 0.95]) },
],
}))
return (
<GestureDetector gesture={tap}>
<Animated.View style={animatedStyle}>
<Text>Press me</Text>
</Animated.View>
</GestureDetector>
)
}
```
Store the press **state** (0 or 1), then derive the scale via `interpolate`.
This keeps the shared value as ground truth. Use `runOnJS` to call JS functions
from worklets. Use `.set()` and `.get()` for React Compiler compatibility.
Reference:
[Gesture Handler Tap Gesture](https://docs.swmansion.com/react-native-gesture-handler/docs/gestures/tap-gesture)

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---
title: Animate Transform and Opacity Instead of Layout Properties
impact: HIGH
impactDescription: GPU-accelerated animations, no layout recalculation
tags: animation, performance, reanimated, transform, opacity
---
## Animate Transform and Opacity Instead of Layout Properties
Avoid animating `width`, `height`, `top`, `left`, `margin`, or `padding`. These trigger layout recalculation on every frame. Instead, use `transform` (scale, translate) and `opacity` which run on the GPU without triggering layout.
**Incorrect (animates height, triggers layout every frame):**
```tsx
import Animated, { useAnimatedStyle, withTiming } from 'react-native-reanimated'
function CollapsiblePanel({ expanded }: { expanded: boolean }) {
const animatedStyle = useAnimatedStyle(() => ({
height: withTiming(expanded ? 200 : 0), // triggers layout on every frame
overflow: 'hidden',
}))
return <Animated.View style={animatedStyle}>{children}</Animated.View>
}
```
**Correct (animates scaleY, GPU-accelerated):**
```tsx
import Animated, { useAnimatedStyle, withTiming } from 'react-native-reanimated'
function CollapsiblePanel({ expanded }: { expanded: boolean }) {
const animatedStyle = useAnimatedStyle(() => ({
transform: [
{ scaleY: withTiming(expanded ? 1 : 0) },
],
opacity: withTiming(expanded ? 1 : 0),
}))
return (
<Animated.View style={[{ height: 200, transformOrigin: 'top' }, animatedStyle]}>
{children}
</Animated.View>
)
}
```
**Correct (animates translateY for slide animations):**
```tsx
import Animated, { useAnimatedStyle, withTiming } from 'react-native-reanimated'
function SlideIn({ visible }: { visible: boolean }) {
const animatedStyle = useAnimatedStyle(() => ({
transform: [
{ translateY: withTiming(visible ? 0 : 100) },
],
opacity: withTiming(visible ? 1 : 0),
}))
return <Animated.View style={animatedStyle}>{children}</Animated.View>
}
```
GPU-accelerated properties: `transform` (translate, scale, rotate), `opacity`. Everything else triggers layout.

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---
title: Use Compound Components Over Polymorphic Children
impact: MEDIUM
impactDescription: flexible composition, clearer API
tags: design-system, components, composition
---
## Use Compound Components Over Polymorphic Children
Don't create components that can accept a string if they aren't a text node. If
a component can receive a string child, it must be a dedicated `*Text`
component. For components like buttons, which can have both a View (or
Pressable) together with text, use compound components, such a `Button`,
`ButtonText`, and `ButtonIcon`.
**Incorrect (polymorphic children):**
```tsx
import { Pressable, Text } from 'react-native'
type ButtonProps = {
children: string | React.ReactNode
icon?: React.ReactNode
}
function Button({ children, icon }: ButtonProps) {
return (
<Pressable>
{icon}
{typeof children === 'string' ? <Text>{children}</Text> : children}
</Pressable>
)
}
// Usage is ambiguous
<Button icon={<Icon />}>Save</Button>
<Button><CustomText>Save</CustomText></Button>
```
**Correct (compound components):**
```tsx
import { Pressable, Text } from 'react-native'
function Button({ children }: { children: React.ReactNode }) {
return <Pressable>{children}</Pressable>
}
function ButtonText({ children }: { children: React.ReactNode }) {
return <Text>{children}</Text>
}
function ButtonIcon({ children }: { children: React.ReactNode }) {
return <>{children}</>
}
// Usage is explicit and composable
<Button>
<ButtonIcon><SaveIcon /></ButtonIcon>
<ButtonText>Save</ButtonText>
</Button>
<Button>
<ButtonText>Cancel</ButtonText>
</Button>
```

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