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Getting StartedMigrateReact Native / Expo

React Native / Expo

Status: move the logic, keep the toolchain. Metro (the RN bundler) and the Expo CLI’s start don’t run under 3va yet. Reducers, validation, formatting and API clients do, with their tests. See example 11 and example 12.

What we tried

3va create expo-app expo-app --template blank-typescript
cd expo-app

1. 3va create isn’t sandboxed. It runs create-expo-app through npm exec. That scaffolder then runs npm install itself, which leaves a package-lock.json and a node_modules behind. That install runs lifecycle scripts, with no 3va permissions involved.

2. 3va install is blocked by the scanner. On a fresh install, 10 packages are rejected: commander, open, metro-runtime, @expo/env, @expo/metro-config, @expo/expo-modules-macros-plugin, react-devtools-core and @react-native/debugger-frontend (some in two versions). expo itself now passes. Trust the reviewed versions in "3va": { "trusted": [...] } (or use --no-scan), and the install completes (about 2.5 min for the blank template).

3. The Expo CLI loads, Metro doesn’t:

$ 3va run node_modules/expo/bin/cli --allow-read --allow-write --allow-env \
    --allow-net --allow-child-process -- --version
57.0.27

$ 3va run node_modules/expo/bin/cli … -- start
TypeError: _nodeModule(...).default._nodeModulePaths is not a function
    at resolveFrom
    at getExpoSDKVersionFromPackage

require("module")._nodeModulePaths isn’t implemented in 3va’s module builtin, so Expo can’t even read its config.

4. 3va dev is not for React Native. 3va create expo-app prints Next steps: 3va install && 3va dev, but 3va dev tries to web-bundle react-native itself and fails on its image assets (…/react-native/Libraries/Image/foo.png: No such file or directory).

A setup that works today

package.json
{
  "scripts": {
    "start": "expo start",
    "android": "expo run:android",
    "test": "3va test"
  }
}
  • Install and run Metro/Expo with npm (or your current package manager).
  • Keep business logic in plain .ts files that don’t import react-native or expo-*. They run and test under 3va without an emulator (3va run src/logic.ts --allow-read=./src, 3va test).
  • Run build/codegen scripts with 3va run and exact permissions.

Things to keep in mind

  • Component tests (@testing-library/react-native, jest-expo presets, jest.mock of native modules) belong to the RN Jest setup. 3va test covers pure logic.
  • EAS builds, native modules and expo prebuild are outside 3va’s scope.
  • Bare React Native (@react-native-community/cli) uses the same Metro and has the same limitations.
Next.jsTauri