The first post made the case for Module Federation. This one builds the smallest real version of it: two separate React Native apps, where one app (the host) loads a screen from the other (a remote) while it’s running. We go from an empty folder to a running app, every step shown.
The finished code is in the companion repo at the tag for this post, so you can clone it and diff against your own if something drifts:
git clone https://github.com/warrendeleon/react-native-module-federation
git checkout post-02-first-remoteThis is what you’ll have at the end. The list of Pokémon on screen lives in, and is served by, a different app from the one running:
Two apps
A federation needs a host and at least one remote. Create two fresh React Native apps:
mkdir react-native-module-federation && cd react-native-module-federation
npx @react-native-community/cli@latest init Host --directory apps/host
npx @react-native-community/cli@latest init List --directory apps/listhost is the shell the user launches. list is a feature that will be loaded into it at runtime.
Put both on Re.Pack
React Native ships with Metro. Module Federation 2.0 runs on Re.Pack (Rspack underneath), so the first job is to swap the bundler. The steps are identical in both apps.
Install the bundler and the federation packages in each app:
npm install -D @callstack/repack @rspack/core \
@module-federation/enhanced @module-federation/runtime @swc/helpers@swc/helpers is the easy one to miss. Re.Pack compiles your code with SWC (the Speedy Web Compiler, a Rust-based alternative to Babel that it uses underneath). When SWC compiles modern syntax down, it emits require("@swc/helpers/…") calls to a small shared helper library rather than inlining the same boilerplate everywhere. Miss the package and the build fails with a screen of “can’t resolve” errors that give no hint of the real cause.
Now point the React Native CLI at Re.Pack. In both apps, add react-native.config.js:
// apps/host/react-native.config.js AND apps/list/react-native.config.js
module.exports = {
commands: require('@callstack/repack/commands/rspack'),
};That single file is what makes react-native start and react-native bundle use Rspack instead of Metro. The bundler is swapped. What differs between host and remote is the rspack.config.mjs each one gets, which is where federation is configured.
The remote: expose a screen
A federated remote is an app with no AppRegistry.registerComponent. It doesn’t boot itself, it waits to be pulled into a host. It declares a name and what it hands out.
First the screen it hands out, apps/list/src/PokedexScreen.tsx. Plain React Native on purpose, this post is about loading it, not styling it:
import React from 'react';
import { FlatList, StyleSheet, Text, View } from 'react-native';
const POKEMON = [
{ id: 1, name: 'Bulbasaur' },
{ id: 4, name: 'Charmander' },
{ id: 7, name: 'Squirtle' },
{ id: 25, name: 'Pikachu' },
{ id: 133, name: 'Eevee' },
];
export default function PokedexScreen() {
return (
<View style={styles.screen}>
<Text style={styles.title}>Pokédex</Text>
<Text style={styles.subtitle}>Served by the list remote</Text>
<FlatList
data={POKEMON}
keyExtractor={p => String(p.id)}
renderItem={({ item }) => (
<View style={styles.row}>
<Text style={styles.number}>#{String(item.id).padStart(3, '0')}</Text>
<Text style={styles.name}>{item.name}</Text>
</View>
)}
/>
</View>
);
}
const styles = StyleSheet.create({
screen: { flex: 1, padding: 24, backgroundColor: '#fff' },
title: { fontSize: 28, fontWeight: '700' },
subtitle: { fontSize: 14, color: '#6b7280', marginBottom: 16 },
row: {
flexDirection: 'row',
paddingVertical: 12,
borderBottomWidth: StyleSheet.hairlineWidth,
borderBottomColor: '#e5e7eb',
},
number: { width: 56, color: '#9ca3af', fontVariant: ['tabular-nums'] },
name: { fontSize: 16, fontWeight: '500' },
});The container’s entry point, apps/list/src/index.js, is almost empty. A remote registers no root component, so it has nothing to do at startup:
// apps/list/src/index.js
export {};Now the config, apps/list/rspack.config.mjs:
import path from 'node:path';
import { fileURLToPath } from 'node:url';
import * as Repack from '@callstack/repack';
import pkg from './package.json' with { type: 'json' };
const __dirname = path.dirname(fileURLToPath(import.meta.url));
export default Repack.defineRspackConfig(env => {
const { mode, platform } = env;
return {
mode,
context: __dirname,
entry: './src/index.js',
resolve: {
// Lets the resolver read each package's `exports` map, which the Module Federation
// runtime needs for subpath imports like '@module-federation/runtime/helpers'.
...Repack.getResolveOptions({ enablePackageExports: true }),
},
output: {
path: `${__dirname}/build/[platform]`,
uniqueName: 'ListApp',
},
module: {
rules: [
{
test: /\.[cm]?[jt]sx?$/,
type: 'javascript/auto',
use: { loader: '@callstack/repack/babel-swc-loader', parallel: true, options: {} },
},
...Repack.getAssetTransformRules(),
],
},
plugins: [
new Repack.RepackPlugin({
extraChunks: [
{ include: /.*/, type: 'remote', outputPath: `build/${platform}/remote` },
],
}),
new Repack.plugins.ModuleFederationPluginV2({
name: 'listApp',
filename: 'listApp.container.js.bundle',
exposes: {
'./PokedexScreen': './src/PokedexScreen.tsx',
},
dts: false,
shared: {
react: { singleton: true, requiredVersion: pkg.dependencies.react },
'react-native': {
singleton: true,
requiredVersion: pkg.dependencies['react-native'],
},
},
}),
],
};
});Three things in there matter. exposes maps a public key, ./PokedexScreen, to a file. That key is the remote’s entire public surface. shared declares react and react-native as singletons, so the remote renders against the host’s one copy instead of bundling its own (two Reacts in one runtime would break hooks). And enablePackageExports: true is not optional: without it the federation runtime can’t resolve its own subpath imports and the build fails.
Add a dev-server script to apps/list/package.json:
"scripts": {
"start:remote": "react-native start --config rspack.config.mjs --port 8082"
}Start it:
cd apps/list && npm run start:remoteIt serves a manifest at http://localhost:8082/ios/mf-manifest.json describing the container and the screen it exposes. Open that URL and you’ll see ./PokedexScreen listed. The remote renders nothing on its own, it’s a feature waiting for an app.
The host: load the remote
The host is an ordinary React Native app. Its apps/host/rspack.config.mjs consumes the remote:
import path from 'node:path';
import { fileURLToPath } from 'node:url';
import * as Repack from '@callstack/repack';
import pkg from './package.json' with { type: 'json' };
const __dirname = path.dirname(fileURLToPath(import.meta.url));
export default Repack.defineRspackConfig(env => {
const { mode, platform } = env;
return {
mode,
context: __dirname,
entry: './index.js',
resolve: {
...Repack.getResolveOptions({ enablePackageExports: true }),
},
output: {
path: `${__dirname}/build/[platform]`,
uniqueName: 'Host',
},
module: {
rules: [
{
test: /\.[cm]?[jt]sx?$/,
type: 'javascript/auto',
use: { loader: '@callstack/repack/babel-swc-loader', parallel: true, options: {} },
},
...Repack.getAssetTransformRules(),
],
},
plugins: [
new Repack.RepackPlugin(),
new Repack.plugins.ModuleFederationPluginV2({
name: 'host',
filename: 'host.container.js.bundle',
remotes: {
// name@url: the host knows listApp lives at this manifest URL. In dev that is the
// remote's own dev server on :8082.
listApp: `listApp@http://localhost:8082/${platform}/mf-manifest.json`,
},
dts: false,
shared: {
react: { singleton: true, eager: true, requiredVersion: pkg.dependencies.react },
'react-native': {
singleton: true,
eager: true,
requiredVersion: pkg.dependencies['react-native'],
},
},
}),
],
};
});The name@url line is the whole wiring: the host knows a remote called listApp sits at that manifest URL. The host’s shared adds eager: true, because the host is the one copy everyone renders against, and eager makes the share scope ready before the synchronous app entry runs, so no bootstrap file is needed.
Now load it. Replace apps/host/App.tsx:
import React, { Suspense } from 'react';
import { ActivityIndicator, SafeAreaView, StyleSheet } from 'react-native';
const PokedexScreen = React.lazy(() => import('listApp/PokedexScreen'));
export default function App() {
return (
<SafeAreaView style={styles.root}>
<Suspense fallback={<ActivityIndicator style={styles.loader} size="large" />}>
<PokedexScreen />
</Suspense>
</SafeAreaView>
);
}
const styles = StyleSheet.create({
root: { flex: 1 },
loader: { flex: 1 },
});listApp/PokedexScreen is not a package on disk. It’s the listApp from the host’s remotes, then the ./PokedexScreen that remote exposed. At runtime, Module Federation turns that import into “fetch listApp’s container from its URL, start it, return its PokedexScreen export”. Because it’s a dynamic import returning a promise, it fits directly into React.lazy with a Suspense spinner while the remote downloads.
TypeScript doesn’t know that specifier, so tell it the shape. Add apps/host/mf-modules.d.ts:
declare module 'listApp/PokedexScreen' {
import type React from 'react';
const PokedexScreen: React.ComponentType;
export default PokedexScreen;
}ScriptManager: the part that’s different on native
Everything above would look familiar to anyone who’s done Module Federation on the web. React Native is where it diverges.
On the web, import('listApp/PokedexScreen') ends in the browser fetching a script over HTTP and the engine running it. A browser does that constantly. Loading code from a URL is routine for it. A React Native runtime has no equivalent. No DOM, no <script> tag, no built-in way to pull in more code on demand once the app has booted. A standard RN app is one self-contained bundle, loaded at launch, with nothing in it that knows how to go and fetch another chunk later.
Re.Pack fills that gap with ScriptManager: the piece that turns a request the federation runtime makes (“I need listApp’s container”) into the real steps, work out the URL, fetch the script, hand it to the engine to run, cache it. On native, every federated import goes through it.
The good news for this post: in dev you write none of it. The Module Federation plugin you already added auto-wires ScriptManager and a default resolver that knows how to reach the remote’s dev server. So the full loop is just:
sequenceDiagram
participant Host as Host app
participant MF as MF runtime
participant SM as ScriptManager
participant Dev as list dev server :8082
Host->>MF: import('listApp/PokedexScreen')
MF->>SM: fetch listApp container
SM->>Dev: GET the container + chunks
Dev-->>SM: JavaScript
SM-->>MF: executed module
MF-->>Host: PokedexScreen component
Host->>Host: render it
When you move to production, ScriptManager is where the real work is: resolving versioned CDN URLs, verifying a signature before running anything, falling back to an embedded copy when the network fails. All later in the series. For now it’s enough to know it’s the bridge between “import a remote” and “code arrives over the wire and runs” that the browser gave web federation for free.
Run it
The host has the native iOS project, the remote is JS-only. So pods are installed for the host only:
cd apps/host/ios && bundle install && bundle exec pod installThen, in three terminals:
# 1. the remote's dev server (leave the one from earlier running, or start it)
cd apps/list && npm run start:remote # :8082
# 2. the host's dev server
cd apps/host && npm start # :8081
# 3. build and launch the host on a simulator
cd apps/host && npm run iosThe host boots, shows the spinner briefly while it fetches listApp from :8082, then renders the Pokédex screen, served by a completely separate app.
To prove they really are separate, stop the list dev server and reload the host. The screen can’t load. Making that degrade to something safe, an offline copy built into the host, is its own post later in the series. Right now the basic loop is what matters, and it runs.
What you built, and what’s still minimal
You have two apps that build and deploy on their own, joined at runtime. The host imports a screen by name, and the code arrives over the network and runs inside it. The remote compiled nothing into the host.
Two things were kept deliberately minimal, each its own post:
- The shared libraries. react and react-native are shared so the remote renders against the host’s copy. The full contract, eager versus lazy, version skew, and the mistake that breaks it silently, is the next post.
- Everything production needs. Versioned CDN loads, signing, an offline fallback, and what happens when a remote is gone. The second half of the series.
Next: the shared-singleton contract, and the one mistake that fails it silently.
Sources
- Re.Pack — the React Native bundler that wraps Rspack and provides ScriptManager and Module Federation support
- Module Federation 2.0 — the runtime architecture behind
name@urlremotes andexposes - react-native-module-federation — the companion repo, at the tag
post-02-first-remote
