When to Use API Routes

Use API routes when you need:

•Server-side secrets — API keys, database credentials, or tokens that must never reach the client
•Database operations — Direct database queries that shouldn't be exposed
•Third-party API proxies — Hide API keys when calling external services (OpenAI, Stripe, etc.)
•Server-side validation — Validate data before database writes
•Webhook endpoints — Receive callbacks from services like Stripe or GitHub
•Rate limiting — Control access at the server level
•Heavy computation — Offload processing that would be slow on mobile

When NOT to Use API Routes

Avoid API routes when:

•Data is already public — Use direct fetch to public APIs instead
•No secrets required — Static data or client-safe operations
•Real-time updates needed — Use WebSockets or services like Supabase Realtime
•Simple CRUD — Consider Firebase, Supabase, or Convex for managed backends
•File uploads — Use direct-to-storage uploads (S3 presigned URLs, Cloudflare R2)
•Authentication only — Use Clerk, Auth0, or Firebase Auth instead

File Structure

API routes live in the app directory with +api.ts suffix:

code

app/
  api/
    hello+api.ts          → GET /api/hello
    users+api.ts          → /api/users
    users/[id]+api.ts     → /api/users/:id
  (tabs)/
    index.tsx

Basic API Route

// app/api/hello+api.ts
export function GET(request: Request) {
  return Response.json({ message: 'Hello from Expo!' });
}

HTTP Methods

Export named functions for each HTTP method:

// app/api/items+api.ts
export function GET(request: Request) {
  return Response.json({ items: [] });
}

export async function POST(request: Request) {
  const body = await request.json();
  return Response.json({ created: body }, { status: 201 });
}

export async function PUT(request: Request) {
  const body = await request.json();
  return Response.json({ updated: body });
}

export async function DELETE(request: Request) {
  return new Response(null, { status: 204 });
}

Dynamic Routes

// app/api/users/[id]+api.ts
export function GET(request: Request, { id }: { id: string }) {
  return Response.json({ userId: id });
}

Request Handling

Query Parameters

export function GET(request: Request) {
  const url = new URL(request.url);
  const page = url.searchParams.get('page') ?? '1';
  const limit = url.searchParams.get('limit') ?? '10';

  return Response.json({ page, limit });
}

Headers

export function GET(request: Request) {
  const auth = request.headers.get('Authorization');

  if (!auth) {
    return Response.json({ error: 'Unauthorized' }, { status: 401 });
  }

  return Response.json({ authenticated: true });
}

JSON Body

export async function POST(request: Request) {
  const { email, password } = await request.json();

  if (!email || !password) {
    return Response.json({ error: 'Missing fields' }, { status: 400 });
  }

  return Response.json({ success: true });
}

Environment Variables

Use process.env for server-side secrets:

// app/api/ai+api.ts
export async function POST(request: Request) {
  const { prompt } = await request.json();

  const response = await fetch('https://api.openai.com/v1/chat/completions', {
    method: 'POST',
    headers: {
      'Content-Type': 'application/json',
      Authorization: `Bearer ${process.env.OPENAI_API_KEY}`,
    },
    body: JSON.stringify({
      model: 'gpt-4',
      messages: [{ role: 'user', content: prompt }],
    }),
  });

  const data = await response.json();
  return Response.json(data);
}

Set environment variables:

•Local: Create .env file (never commit)
•EAS Hosting: Use eas env:create or Expo dashboard

CORS Headers

Add CORS for web clients:

const corsHeaders = {
  'Access-Control-Allow-Origin': '*',
  'Access-Control-Allow-Methods': 'GET, POST, PUT, DELETE, OPTIONS',
  'Access-Control-Allow-Headers': 'Content-Type, Authorization',
};

export function OPTIONS() {
  return new Response(null, { headers: corsHeaders });
}

export function GET() {
  return Response.json({ data: 'value' }, { headers: corsHeaders });
}

Error Handling

export async function POST(request: Request) {
  try {
    const body = await request.json();
    // Process...
    return Response.json({ success: true });
  } catch (error) {
    console.error('API error:', error);
    return Response.json({ error: 'Internal server error' }, { status: 500 });
  }
}

Testing Locally

Start the development server with API routes:

bash

bunx expo serve

This starts a local server at http://localhost:8081 with full API route support.

Test with curl:

bash

curl http://localhost:8081/api/hello
curl -X POST http://localhost:8081/api/users -H "Content-Type: application/json" -d '{"name":"Test"}'

Deployment to EAS Hosting

Prerequisites

bash

bun install -g eas-cli
eas login

Deploy

bash

eas deploy

This builds and deploys your API routes to EAS Hosting (Cloudflare Workers).

Environment Variables for Production

bash

# Create a secret
eas env:create --name OPENAI_API_KEY --value sk-xxx --environment production

# Or use the Expo dashboard

Custom Domain

Configure in eas.json or Expo dashboard.

EAS Hosting Runtime (Cloudflare Workers)

API routes run on Cloudflare Workers. Key limitations:

Missing/Limited APIs

•No Node.js filesystem — fs module unavailable
•No native Node modules — Use Web APIs or polyfills
•Limited execution time — 30 second timeout for CPU-intensive tasks
•No persistent connections — WebSockets require Durable Objects
•fetch is available — Use standard fetch for HTTP requests

Use Web APIs Instead

// Use Web Crypto instead of Node crypto
const hash = await crypto.subtle.digest('SHA-256', new TextEncoder().encode('data'));

// Use fetch instead of node-fetch
const response = await fetch('https://api.example.com');

// Use Response/Request (already available)
return new Response(JSON.stringify(data), {
  headers: { 'Content-Type': 'application/json' },
});

Database Options

Since filesystem is unavailable, use cloud databases:

•Cloudflare D1 — SQLite at the edge
•Turso — Distributed SQLite
•PlanetScale — Serverless MySQL
•Supabase — Postgres with REST API
•Neon — Serverless Postgres

Example with Turso:

// app/api/users+api.ts
import { createClient } from '@libsql/client/web';

const db = createClient({
  url: process.env.TURSO_URL!,
  authToken: process.env.TURSO_AUTH_TOKEN!,
});

export async function GET() {
  const result = await db.execute('SELECT * FROM users');
  return Response.json(result.rows);
}

Calling API Routes from Client

// From React Native components
const response = await fetch('/api/hello');
const data = await response.json();

// With body
const response = await fetch('/api/users', {
  method: 'POST',
  headers: { 'Content-Type': 'application/json' },
  body: JSON.stringify({ name: 'John' }),
});

Common Patterns

Authentication Middleware

// utils/auth.ts
export async function requireAuth(request: Request) {
  const token = request.headers.get('Authorization')?.replace('Bearer ', '');

  if (!token) {
    throw new Response(JSON.stringify({ error: 'Unauthorized' }), {
      status: 401,
      headers: { 'Content-Type': 'application/json' },
    });
  }

  // Verify token...
  return { userId: '123' };
}

// app/api/protected+api.ts
import { requireAuth } from '../../utils/auth';

export async function GET(request: Request) {
  const { userId } = await requireAuth(request);
  return Response.json({ userId });
}

Proxy External API

// app/api/weather+api.ts
export async function GET(request: Request) {
  const url = new URL(request.url);
  const city = url.searchParams.get('city');

  const response = await fetch(
    `https://api.weather.com/v1/current?city=${city}&key=${process.env.WEATHER_API_KEY}`
  );

  return Response.json(await response.json());
}

Rules

•NEVER expose API keys or secrets in client code
•ALWAYS validate and sanitize user input
•Use proper HTTP status codes (200, 201, 400, 401, 404, 500)
•Handle errors gracefully with try/catch
•Keep API routes focused — one responsibility per endpoint
•Use TypeScript for type safety
•Log errors server-side for debugging