Function API

EventContext

interface EventContext {
  request: Request;              // Incoming request
  functionPath: string;          // Request path
  waitUntil(promise: Promise<any>): void;  // Background tasks (non-blocking)
  passThroughOnException(): void;          // Fallback to static on error
  next(input?: Request | string, init?: RequestInit): Promise;
  env: Env;                      // Bindings, vars, secrets
  params: Record<string, string | string[]>;  // Route params ([user] or [[catchall]])
  data: any;                     // Middleware shared state
}

TypeScript: See configuration.md for wrangler types setup

Handlers

// Generic (fallback for any method)

  return new Response('Any method');
}

// Method-specific (takes precedence over generic)

  return Response.json({ message: 'GET' });
}

  const body = await ctx.request.json();
  return Response.json({ received: body });
}
// Also: onRequestPut, onRequestPatch, onRequestDelete, onRequestHead, onRequestOptions

Bindings Reference

See configuration.md for wrangler.jsonc examples.

Bindings

KV

interface Env { KV: KVNamespace; }

  await ctx.env.KV.put('key', 'value', { expirationTtl: 3600 });
  const val = await ctx.env.KV.get('key', { type: 'json' });
  const keys = await ctx.env.KV.list({ prefix: 'user:' });
  return Response.json({ val });
};

D1

interface Env { DB: D1Database; }

  const user = await ctx.env.DB.prepare('SELECT * FROM users WHERE id = ?').bind(123).first();
  return Response.json(user);
};

R2

interface Env { BUCKET: R2Bucket; }

  const obj = await ctx.env.BUCKET.get('file.txt');
  if (!obj) return new Response('Not found', { status: 404 });
  await ctx.env.BUCKET.put('file.txt', ctx.request.body);
  return new Response(obj.body);
};

Durable Objects

interface Env { COUNTER: DurableObjectNamespace; }

  const stub = ctx.env.COUNTER.get(ctx.env.COUNTER.idFromName('global'));
  return stub.fetch(ctx.request);
};

Workers AI

interface Env { AI: Ai; }

  const resp = await ctx.env.AI.run('@cf/meta/llama-3.1-8b-instruct', { prompt: 'Hello' });
  return Response.json(resp);
};

Service Bindings & Env Vars

interface Env { AUTH: Fetcher; API_KEY: string; }

  // Service binding: forward to another Worker
  return ctx.env.AUTH.fetch(ctx.request);
  
  // Environment variable
  return Response.json({ key: ctx.env.API_KEY });
};

Advanced Mode (env.ASSETS)

When using _worker.js, access static assets via env.ASSETS.fetch():

interface Env { ASSETS: Fetcher; KV: KVNamespace; }

  async fetch(request: Request, env: Env): Promise {
    const url = new URL(request.url);
    if (url.pathname.startsWith('/api/')) {
      return Response.json({ data: await env.KV.get('key') });
    }
    return env.ASSETS.fetch(request); // Fallback to static
  }
} satisfies ExportedHandler;

See also: configuration.md for TypeScript setup and wrangler.jsonc | patterns.md for middleware and auth patterns