@base44/metro-plugin

Metro/Expo plugin for Base44 native-mobile applications running in sandboxed preview iframes. It injects the preview runtime that the Base44 builder consumes over postMessage — navigation, mount, HMR, and error signals — the Metro counterpart to @base44/vite-plugin.

Status: scaffold. The withBase44 wrapper is published and stable as an API, but is currently a no-op pass-through. Runtime injection lands in a follow-up (Phase 0). Wiring it into the template now lets behavior arrive via version bumps.

Installation

npm install @base44/metro-plugin

Usage

// metro.config.js
const { getDefaultConfig } = require("expo/metro-config");
const { withNativeWind } = require("nativewind/metro");
const { withBase44 } = require("@base44/metro-plugin/metro");

const config = getDefaultConfig(__dirname);

module.exports = withBase44(withNativeWind(config, { input: "./global.css" }));

withBase44 is sandbox-gated on MODAL_SANDBOX_ID: outside a Base44 preview sandbox it returns the config untouched, so it's a no-op for local expo start.

Options

withBase44(config, {
  navigationNotifier: true, // app_changed_url on expo-router navigation
  hmrNotifier: true,        // sandbox:beforeUpdate / sandbox:afterUpdate
  errorNotifier: true,      // forward runtime errors as app_error
});

Why Metro, not Vite

The mobile bundler is Metro (Expo orchestrates it). This package plugs into Metro's config API — a withBase44(config) wrapper, exactly like nativewind/metro's withNativeWind. It is not an Expo config plugin (those mutate native project config at prebuild); it is a Metro plugin.

Development

npm install
npm run build      # tsc -> dist (CommonJS, so metro.config.js can require it)
npm run test:unit