cloudflare-workers

name	cloudflare-workers
description	Cloudflare Workers development guide for building serverless edge applications. Use this skill when creating Workers, configuring wrangler.toml, using D1/KV/R2 storage, implementing Durable Objects, deploying to Cloudflare, or building edge functions with TypeScript.

Cloudflare Workers Development

Overview

Build serverless applications on Cloudflare's edge platform with millisecond cold starts using V8 isolates.

Prerequisites

# Install Wrangler CLI
npm install -g wrangler

# Authenticate
wrangler login

# Create new project
npm create cloudflare@latest my-worker

Project Structure

my-worker/
├── src/
│   └── index.ts          # Entry point
├── wrangler.toml         # Configuration
├── package.json
└── tsconfig.json

Basic Worker

export default {
  async fetch(request: Request, env: Env, ctx: ExecutionContext): Promise<Response> {
    const url = new URL(request.url);

    if (url.pathname === '/api/hello') {
      return Response.json({ message: 'Hello from the edge!' });
    }

    return new Response('Not Found', { status: 404 });
  },
} satisfies ExportedHandler<Env>;

Configuration (wrangler.toml)

name = "my-worker"
main = "src/index.ts"
compatibility_date = "2024-01-01"

# Environment variables
[vars]
API_VERSION = "v1"

# D1 Database
[[d1_databases]]
binding = "DB"
database_name = "my-database"
database_id = "xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx"

# KV Namespace
[[kv_namespaces]]
binding = "KV"
id = "xxxxxxxx"

# R2 Bucket
[[r2_buckets]]
binding = "BUCKET"
bucket_name = "my-bucket"

# Durable Objects
[[durable_objects.bindings]]
name = "COUNTER"
class_name = "Counter"

[[migrations]]
tag = "v1"
new_classes = ["Counter"]

# Queues
[[queues.producers]]
queue = "my-queue"
binding = "QUEUE"

[[queues.consumers]]
queue = "my-queue"
max_batch_size = 10

# Scheduled (Cron)

 = []  

Storage Patterns

D1 (SQLite Database)

interface Env {
  DB: D1Database;
}

// Query
const { results } = await env.DB.prepare(
  'SELECT * FROM users WHERE id = ?'
).bind(userId).all();

// Insert
await env.DB.prepare(
  'INSERT INTO users (name, email) VALUES (?, ?)'
).bind(name, email).run();

// Batch operations
await env.DB.batch([
  env.DB.prepare('INSERT INTO logs (msg) VALUES (?)').bind('log1'),
  env.DB.prepare('INSERT INTO logs (msg) VALUES (?)').bind('log2'),
]);

KV (Key-Value Store)

interface Env {
  KV: KVNamespace;
}

// Get with type
const value = await env.KV.get<User>('user:123', 'json');

// Put with TTL (seconds)
await env.KV.put('session:abc', JSON.stringify(data), {
  expirationTtl: 3600,
});

// List keys with prefix
const { keys } = await env.KV.list({ prefix: 'user:' });

// Delete
await env.KV.delete('user:123');

R2 (Object Storage)

interface Env {
  BUCKET: R2Bucket;
}

// Upload
await env.BUCKET.put('files/document.pdf', fileBody, {
  httpMetadata: { contentType: 'application/pdf' },
  customMetadata: { uploadedBy: userId },
});

// Download
const object = await env.BUCKET.get('files/document.pdf');
if (object) {
  return new Response(object.body, {
    headers: { 'Content-Type': object.httpMetadata?.contentType || '' },
  });
}

// Stream large files
const object = await env.BUCKET.get('large-file.zip');
return new Response(object?.body, {
  headers: { 'Content-Disposition': 'attachment; filename="large-file.zip"' },
});

// Delete
await env.BUCKET.delete();

Durable Objects

// Durable Object class
export class Counter implements DurableObject {
  private value: number = 0;

  constructor(private state: DurableObjectState, private env: Env) {
    this.state.blockConcurrencyWhile(async () => {
      this.value = (await this.state.storage.get<number>('value')) || 0;
    });
  }

  async fetch(request: Request): Promise<Response> {
    const url = new URL(request.url);

    if (url.pathname === '/increment') {
      this.value++;
      await this.state.storage.put('value', .);
    }

     .({ : . });
  }
}


  {
   (: , : ): <> {
     id = env..();
     stub = env..(id);
     stub.(request);
  },
};

Durable Objects with WebSocket

export class ChatRoom implements DurableObject {
  private sessions: Map<WebSocket, { name: string }> = new Map();

  async fetch(request: Request): Promise<Response> {
    if (request.headers.get('Upgrade') !== 'websocket') {
      return new Response('Expected WebSocket', { status: 400 });
    }

    const pair = new WebSocketPair();
    const [client, server] = Object.values(pair);

    this.state.acceptWebSocket(server);
    this.sessions.set(server, { name: 'anonymous' });

    return new Response(null, { status: 101, webSocket: client });
  }

  async () {
     data = .(message);

    
     ( [socket]  .) {
      socket.(.(data));
    }
  }

   () {
    ..(ws);
  }
}

Queues

interface Env {
  QUEUE: Queue;
}

// Producer
await env.QUEUE.send({
  type: 'email',
  to: '[e-mail]',
  subject: 'Welcome!',
});

// Send batch
await env.QUEUE.sendBatch([
  { body: { type: 'task1' } },
  { body: { type: 'task2' } },
]);

// Consumer
export default {
  async queue(batch: MessageBatch<QueueMessage>, env: Env): Promise<void> {
    for (const message of batch.messages) {
      try {
        await processMessage(message.body);
        message.ack();
      } catch (error) {
        message.retry();
      }
    }
  },
};

Scheduled Workers (Cron)

export default {
  async scheduled(event: ScheduledEvent, env: Env, ctx: ExecutionContext) {
    ctx.waitUntil(doCleanup(env));
  },
};

// wrangler.toml
// [triggers]
// crons = ["0 0 * * *"]  # Daily at midnight

Authentication Patterns

JWT Verification

import { jwtVerify } from 'jose';

async function verifyToken(token: string, env: Env): Promise<JWTPayload | null> {
  try {
    const secret = new TextEncoder().encode(env.JWT_SECRET);
    const { payload } = await jwtVerify(token, secret);
    return payload;
  } catch {
    return null;
  }
}

// Middleware pattern
async function authMiddleware(request: Request, env: Env): Promise<Response | null> {
  const auth = request.headers.get('Authorization');
  if (!auth?.startsWith('Bearer ')) {
    return Response.json({ error: 'Unauthorized' }, { status: 401 });
  }

   payload =  (auth.(), env);
   (!payload) {
     .({ :  }, { :  });
  }

   ; 
}

Session with KV

async function createSession(userId: string, env: Env): Promise<string> {
  const sessionId = crypto.randomUUID();
  await env.KV.put(`session:${sessionId}`, userId, {
    expirationTtl: 86400, // 24 hours
  });
  return sessionId;
}

async function getSession(sessionId: string, env: Env): Promise<string | null> {
  return env.KV.get(`session:${sessionId}`);
}

Rate Limiting

async function rateLimit(
  key: string,
  limit: number,
  window: number,
  env: Env
): Promise<boolean> {
  const current = await env.KV.get<number>(`ratelimit:${key}`, 'json') || 0;

  if (current >= limit) {
    return false;
  }

  await env.KV.put(`ratelimit:${key}`, JSON.stringify(current + 1), {
    expirationTtl: window,
  });

  return true;
}

// Usage
const allowed = await rateLimit(clientIP, 100, 60, env);
if (!allowed) {
  return Response.json({ error: 'Rate limited' }, { status: 429 });
}

API Routing with Hono

import { Hono } from 'hono';
import { cors } from 'hono/cors';

const app = new Hono<{ Bindings: Env }>();

app.use('*', cors());

app.get('/api/users', async (c) => {
  const { results } = await c.env.DB.prepare('SELECT * FROM users').all();
  return c.json(results);
});

app.post('/api/users', async (c) => {
  const { name, email } = await c.req.json();
  await c.env.DB.prepare('INSERT INTO users (name, email) VALUES (?, ?)')
    .bind(name, email)
    .run();
  return c.json({ success: true }, 201);
});

app.get('/api/users/:id', async (c) => {
  const { results } = await c...()
    .(c..())
    .();
   results[] ? c.(results[]) : c.();
});

  app;

Caching Strategies

// Cache-first with stale-while-revalidate
async function cachedFetch(
  request: Request,
  env: Env,
  ctx: ExecutionContext
): Promise<Response> {
  const cache = caches.default;
  const cacheKey = new Request(request.url, request);

  // Check cache
  let response = await cache.match(cacheKey);

  if (response) {
    // Revalidate in background
    ctx.waitUntil(
      fetch(request).then((fresh) => {
        cache.put(cacheKey, fresh.clone());
      })
    );
    return response;
  }

  // Fetch and cache
  response = await fetch(request);
  ctx.waitUntil(cache.put(cacheKey, response.clone()));

  return response;
}

Development Workflow

# Local development
wrangler dev

# Local with bindings
wrangler dev --local --persist

# Deploy to production
wrangler deploy

# Deploy to staging
wrangler deploy --env staging

# Tail logs
wrangler tail

# Create D1 database
wrangler d1 create my-database

# Run D1 migrations
wrangler d1 migrations apply my-database

# Create KV namespace
wrangler kv:namespace create MY_KV

# Create R2 bucket
wrangler r2 bucket create my-bucket

Testing

import { unstable_dev } from 'wrangler';
import { describe, expect, it, beforeAll, afterAll } from 'vitest';

describe('Worker', () => {
  let worker: UnstableDevWorker;

  beforeAll(async () => {
    worker = await unstable_dev('src/index.ts', {
      experimental: { disableExperimentalWarning: true },
    });
  });

  afterAll(async () => {
    await worker.stop();
  });

  it('responds with hello', async () => {
    const resp = await worker.fetch('/api/hello');
    const data = await resp.json();
    expect(data.message).toBe('Hello from the edge!');
  });
});

Environment Types

interface Env {
  // Variables
  API_VERSION: string;

  // Secrets (set via wrangler secret put)
  JWT_SECRET: string;
  API_KEY: string;

  // Bindings
  DB: D1Database;
  KV: KVNamespace;
  BUCKET: R2Bucket;
  COUNTER: DurableObjectNamespace;
  QUEUE: Queue;
}

See Also

• Reference: wrangler-config.md
• Reference: d1-patterns.md
• Reference: deployment.md