Rn Fundamentals

rn-fundamentals — foundational rules for React Native + Expo

This skill is the prerequisite read for any RN/Expo work. It sets the four non-negotiables and points you to deeper concept material when needed.

The 4 non-negotiables

1. Expo managed workflow is the default. Bare workflow / react-native init only if there is a documented native dependency Expo cannot wrap.
2. Latest stable Expo SDK — 57.0.16 on 2026-08-26 (npm view expo dist-tags); [VERIFY] at bootstrap time, quarterly cadence. New Architecture is on and not optional from SDK 55 onward — do not set newArchEnabled: it is ignored, and confirmed absent from @expo/config-types@57.0.2's ExpoConfig schema (zero occurrences), so it is not merely discouraged — there is no key to set. Hermes is the engine.
3. TypeScript is mandatory. tsconfig.json extends expo/tsconfig.base — confirmed shipping at the root of expo@57.0.16, and it sets moduleResolution: "bundler" (which is why relative imports here need no .js extension). ⚠️ blank-typescript is our choice, not the CLI's default. From create-expo-app@4.0.0's own help: "NPM template to use: default, blank, blank-typescript, tabs, bare-minimum. Default: default" — and default is the one it labels "recommended for most app developers". Pass -t blank-typescript explicitly or you get something else.
4. npm is the package manager. ⚠️ This is a house rule, not the CLI's preference: create-expo-app@4.0.0 resolves the package manager from your environment — the --use-npm / --use-yarn / --use-pnpm flags are gone (zero occurrences in the package). Invoking it with npx gets you npm because npx is npm, not because the CLI prefers it. No Yarn, no pnpm in this set.
5. ⚠️ create-expo-app@4 writes agent files by default — AGENTS.md, CLAUDE.md and .claude/settings.json, opt out with --no-agents-md. On a dev-flow project decide deliberately: a scaffolded CLAUDE.md sitting next to .workflow/ is a second set of instructions nobody reconciled.

Source of truth (Expo)

This skill set (rn-fundamentals + its 6 siblings: rn-data-fetching, rn-expo-router, rn-backend, rn-push-notifications, rn-publishing-payments, rn-animations-gestures) encodes the workflow and opinionated stack choices — Expo managed, New Architecture on, TanStack Query, Reanimated 4, and so on. It is NOT a frozen copy of the Expo/RN API, and it goes stale every time a new SDK ships.

For anything sensitive to the current Expo SDK — exact API shapes, CLI commands and flags, config-plugin options, deprecations, EAS behavior — do not trust this skill's wording blindly. In priority order, the authoritative source is:

1. Live Expo docs — https://docs.expo.dev/ (always current for the installed SDK).
2. Expo MCP server — https://mcp.expo.dev/mcp — live docs/CLI/EAS reference exposed as MCP tools. If it is connected in this session, prefer it over anything written across this skill set for current-version details.
3. Official expo/skills — installable as a Claude Code plugin, or via npx skills add expo/skills — maintained by Expo directly against the SDK release cadence.

Last swept 2026-08-26 against expo@57.0.16, create-expo-app@4.0.0, @expo/config-types@57.0.2 and zustand@5.0.15. Any version number, CLI command, or config key in this skill set marked [VERIFY] above is a candidate to have drifted since — check it against the sources above before relying on it, the same way eve-agent defers to node_modules/eve/docs instead of guessing the eve API.

Quick decision tree

• "Should I use Expo or bare RN?" → references/decision-tree.md
• "What versions am I targeting?" → references/stack-defaults.md
• "Why does X behave differently than React on the web?" → references/concepts.md
• "Is this an OK pattern at the foundational level?" → references/patterns.md
• "Where does this piece of state live?" → references/zustand-rn.md (Zustand as the client-state store: selectors + useShallow, slices, persist with AsyncStorage, ⚠️ the async-hydration race — and the table for what does not belong in it: server data → TanStack Query, form fields → the form lib, ephemeral UI → useState)

Common anti-patterns (NEVER do)

• ❌ npx react-native init when Expo managed would have worked — Expo is the default.
• ❌ Leaving New Architecture OFF on a new project — opt out only with a written reason.
• ❌ Mixing yarn and npm install in the same project.
• ❌ Pinning Expo SDK to a version older than the current stable without justification.

Sources

• Course: codewithbeto.dev/rnCourse — lessons 1, 2, 3, 5, 6, 12 + "Introduction" module (free).
• Official: https://reactnative.dev/architecture/landing-page
• Official: https://docs.expo.dev/get-started/introduction/