1# Function API
2 
3## EventContext
4 
5```typescript
6interface EventContext<Env = any> {
7  request: Request;              // Incoming request
8  functionPath: string;          // Request path
9  waitUntil(promise: Promise<any>): void;  // Background tasks (non-blocking)
10  passThroughOnException(): void;          // Fallback to static on error
11  next(input?: Request | string, init?: RequestInit): Promise<Response>;
12  env: Env;                      // Bindings, vars, secrets
13  params: Record<string, string | string[]>;  // Route params ([user] or [[catchall]])
14  data: any;                     // Middleware shared state
15}
16```
17 
18**TypeScript:** See [configuration.md](./configuration.md) for `wrangler types` setup
19 
20## Handlers
21 
22```typescript
23// Generic (fallback for any method)
24export async function onRequest(ctx: EventContext): Promise<Response> {
25  return new Response('Any method');
26}
27 
28// Method-specific (takes precedence over generic)
29export async function onRequestGet(ctx: EventContext): Promise<Response> {
30  return Response.json({ message: 'GET' });
31}
32 
33export async function onRequestPost(ctx: EventContext): Promise<Response> {
34  const body = await ctx.request.json();
35  return Response.json({ received: body });
36}
37// Also: onRequestPut, onRequestPatch, onRequestDelete, onRequestHead, onRequestOptions
38```
39 
40## Bindings Reference
41 
42| Binding Type | Interface | Config Key | Use Case |
43|--------------|-----------|------------|----------|
44| KV | `KVNamespace` | `kv_namespaces` | Key-value cache, sessions, config |
45| D1 | `D1Database` | `d1_databases` | Relational data, SQL queries |
46| R2 | `R2Bucket` | `r2_buckets` | Large files, user uploads, assets |
47| Durable Objects | `DurableObjectNamespace` | `durable_objects.bindings` | Stateful coordination, websockets |
48| Workers AI | `Ai` | `ai.binding` | LLM inference, embeddings |
49| Vectorize | `VectorizeIndex` | `vectorize` | Vector search, embeddings |
50| Service Binding | `Fetcher` | `services` | Worker-to-worker RPC |
51| Analytics Engine | `AnalyticsEngineDataset` | `analytics_engine_datasets` | Event logging, metrics |
52| Environment Vars | `string` | `vars` | Non-sensitive config |
53 
54See [configuration.md](./configuration.md) for wrangler.jsonc examples.
55 
56## Bindings
57 
58### KV
59 
60```typescript
61interface Env { KV: KVNamespace; }
62export const onRequest: PagesFunction<Env> = async (ctx) => {
63  await ctx.env.KV.put('key', 'value', { expirationTtl: 3600 });
64  const val = await ctx.env.KV.get('key', { type: 'json' });
65  const keys = await ctx.env.KV.list({ prefix: 'user:' });
66  return Response.json({ val });
67};
68```
69 
70### D1
71 
72```typescript
73interface Env { DB: D1Database; }
74export const onRequest: PagesFunction<Env> = async (ctx) => {
75  const user = await ctx.env.DB.prepare('SELECT * FROM users WHERE id = ?').bind(123).first();
76  return Response.json(user);
77};
78```
79 
80### R2
81 
82```typescript
83interface Env { BUCKET: R2Bucket; }
84export const onRequest: PagesFunction<Env> = async (ctx) => {
85  const obj = await ctx.env.BUCKET.get('file.txt');
86  if (!obj) return new Response('Not found', { status: 404 });
87  await ctx.env.BUCKET.put('file.txt', ctx.request.body);
88  return new Response(obj.body);
89};
90```
91 
92### Durable Objects
93 
94```typescript
95interface Env { COUNTER: DurableObjectNamespace; }
96export const onRequest: PagesFunction<Env> = async (ctx) => {
97  const stub = ctx.env.COUNTER.get(ctx.env.COUNTER.idFromName('global'));
98  return stub.fetch(ctx.request);
99};
100```
101 
102### Workers AI
103 
104```typescript
105interface Env { AI: Ai; }
106export const onRequest: PagesFunction<Env> = async (ctx) => {
107  const resp = await ctx.env.AI.run('@cf/meta/llama-3.1-8b-instruct', { prompt: 'Hello' });
108  return Response.json(resp);
109};
110```
111 
112### Service Bindings & Env Vars
113 
114```typescript
115interface Env { AUTH: Fetcher; API_KEY: string; }
116export const onRequest: PagesFunction<Env> = async (ctx) => {
117  // Service binding: forward to another Worker
118  return ctx.env.AUTH.fetch(ctx.request);
119  
120  // Environment variable
121  return Response.json({ key: ctx.env.API_KEY });
122};
123```
124 
125## Advanced Mode (env.ASSETS)
126 
127When using `_worker.js`, access static assets via `env.ASSETS.fetch()`:
128 
129```typescript
130interface Env { ASSETS: Fetcher; KV: KVNamespace; }
131 
132export default {
133  async fetch(request: Request, env: Env): Promise<Response> {
134    const url = new URL(request.url);
135    if (url.pathname.startsWith('/api/')) {
136      return Response.json({ data: await env.KV.get('key') });
137    }
138    return env.ASSETS.fetch(request); // Fallback to static
139  }
140} satisfies ExportedHandler<Env>;
141```
142 
143**See also:** [configuration.md](./configuration.md) for TypeScript setup and wrangler.jsonc | [patterns.md](./patterns.md) for middleware and auth patterns
144