1# Functions API
2 
3## File-Based Routing
4 
5```
6/functions/index.ts              → example.com/
7/functions/api/users.ts          → example.com/api/users
8/functions/api/users/[id].ts     → example.com/api/users/:id
9/functions/api/users/[[path]].ts → example.com/api/users/* (catchall)
10/functions/_middleware.ts        → Runs before all routes
11```
12 
13**Rules**: `[param]` = single segment, `[[param]]` = multi-segment catchall, more specific wins.
14 
15## Request Handlers
16 
17```typescript
18import type { PagesFunction } from '@cloudflare/workers-types';
19 
20interface Env {
21  DB: D1Database;
22  KV: KVNamespace;
23}
24 
25// All methods
26export const onRequest: PagesFunction<Env> = async (context) => {
27  return new Response('All methods');
28};
29 
30// Method-specific
31export const onRequestGet: PagesFunction<Env> = async (context) => {
32  const { request, env, params, data } = context;
33  
34  const user = await env.DB.prepare(
35    'SELECT * FROM users WHERE id = ?'
36  ).bind(params.id).first();
37  
38  return Response.json(user);
39};
40 
41export const onRequestPost: PagesFunction<Env> = async (context) => {
42  const body = await context.request.json();
43  return Response.json({ success: true });
44};
45 
46// Also: onRequestPut, onRequestPatch, onRequestDelete, onRequestHead, onRequestOptions
47```
48 
49## Context Object
50 
51```typescript
52interface EventContext<Env, Params, Data> {
53  request: Request;              // HTTP request
54  env: Env;                      // Bindings (KV, D1, R2, etc.)
55  params: Params;                // Route parameters
56  data: Data;                    // Middleware-shared data
57  waitUntil: (promise: Promise<any>) => void;  // Background tasks
58  next: () => Promise<Response>; // Next handler
59  passThroughOnException: () => void;  // Error fallback (not in advanced mode)
60}
61```
62 
63## Dynamic Routes
64 
65```typescript
66// Single segment: functions/users/[id].ts
67export const onRequestGet: PagesFunction = async ({ params }) => {
68  // /users/123 → params.id = "123"
69  return Response.json({ userId: params.id });
70};
71 
72// Multi-segment: functions/files/[[path]].ts
73export const onRequestGet: PagesFunction = async ({ params }) => {
74  // /files/docs/api/v1.md → params.path = ["docs", "api", "v1.md"]
75  const filePath = (params.path as string[]).join('/');
76  return new Response(filePath);
77};
78```
79 
80## Middleware
81 
82```typescript
83// functions/_middleware.ts
84// Single
85export const onRequest: PagesFunction = async (context) => {
86  const response = await context.next();
87  response.headers.set('X-Custom-Header', 'value');
88  return response;
89};
90 
91// Chained (runs in order)
92const errorHandler: PagesFunction = async (context) => {
93  try {
94    return await context.next();
95  } catch (err) {
96    return new Response(err.message, { status: 500 });
97  }
98};
99 
100const auth: PagesFunction = async (context) => {
101  const token = context.request.headers.get('Authorization');
102  if (!token) return new Response('Unauthorized', { status: 401 });
103  context.data.userId = await verifyToken(token);
104  return context.next();
105};
106 
107export const onRequest = [errorHandler, auth];
108```
109 
110**Scope**: `functions/_middleware.ts` → all; `functions/api/_middleware.ts` → `/api/*` only
111 
112## Bindings Usage
113 
114```typescript
115export const onRequestGet: PagesFunction<Env> = async ({ env }) => {
116  // KV
117  const cached = await env.KV.get('key', 'json');
118  await env.KV.put('key', JSON.stringify({data: 'value'}), {expirationTtl: 3600});
119  
120  // D1
121  const result = await env.DB.prepare('SELECT * FROM users WHERE id = ?').bind(userId).first();
122  
123  // R2, Queue, AI - see respective reference docs
124  
125  return Response.json({success: true});
126};
127```
128 
129## Advanced Mode
130 
131Full Workers API, bypasses file-based routing:
132 
133```javascript
134// functions/_worker.js
135export default {
136  async fetch(request, env, ctx) {
137    const url = new URL(request.url);
138    
139    // Custom routing
140    if (url.pathname.startsWith('/api/')) {
141      return new Response('API response');
142    }
143    
144    // REQUIRED: Serve static assets
145    return env.ASSETS.fetch(request);
146  }
147};
148```
149 
150**When to use**: WebSockets, complex routing, scheduled handlers, email handlers.
151 
152## Smart Placement
153 
154Automatically optimizes function execution location based on traffic patterns.
155 
156**Configuration** (in wrangler.jsonc):
157```jsonc
158{
159  "placement": {
160    "mode": "smart"  // Enables optimization (default: off)
161  }
162}
163```
164 
165**How it works**: Analyzes traffic patterns over time and places functions closer to users or data sources (e.g., D1 databases). Requires no code changes.
166 
167**Trade-offs**: Initial requests may see slightly higher latency during learning period (hours-days). Performance improves as system optimizes.
168 
169**When to use**: Global apps with centralized databases or geographically concentrated traffic sources.
170 
171## getRequestContext (Framework SSR)
172 
173Access bindings in framework code:
174 
175```typescript
176// SvelteKit
177import type { RequestEvent } from '@sveltejs/kit';
178export async function load({ platform }: RequestEvent) {
179  const data = await platform.env.DB.prepare('SELECT * FROM users').all();
180  return { users: data.results };
181}
182 
183// Astro
184const { DB } = Astro.locals.runtime.env;
185const data = await DB.prepare('SELECT * FROM users').all();
186 
187// Solid Start (server function)
188import { getRequestEvent } from 'solid-js/web';
189const event = getRequestEvent();
190const data = await event.locals.runtime.env.DB.prepare('SELECT * FROM users').all();
191```
192 
193**✅ Supported adapters** (2026):
194- **SvelteKit**: `@sveltejs/adapter-cloudflare`
195- **Astro**: Built-in Cloudflare adapter
196- **Nuxt**: Set `nitro.preset: 'cloudflare-pages'` in `nuxt.config.ts`
197- **Qwik**: Built-in Cloudflare adapter
198- **Solid Start**: `@solidjs/start-cloudflare-pages`
199 
200**❌ Deprecated/Unsupported**:
201- **Next.js**: Official adapter (`@cloudflare/next-on-pages`) deprecated. Use Vercel or self-host on Workers.
202- **Remix**: Official adapter (`@remix-run/cloudflare-pages`) deprecated. Migrate to supported frameworks.
203 
204See [gotchas.md](./gotchas.md#framework-specific) for migration guidance.
205