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:

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:

npx expo serve

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

Test with curl:

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 npm install -g eas-cli eas login

Deploy eas deploy

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

Environment Variables for Production

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