cloudflare-worker-dev

Cloudflare Workers Development

Build high-performance edge APIs with Workers, KV for caching, and Durable Objects for real-time coordination.

Core Architecture

When to Use What

Service	Use Case	Characteristics
Workers	Request handling, API logic	Stateless, 50ms CPU (free), 30s (paid)
KV	Caching, config, sessions	Eventually consistent, fast reads
Durable Objects	Real-time, coordination	Strongly consistent, single-threaded
R2	File storage	S3-compatible, no egress fees
D1	SQLite at edge	Serverless SQL, good for reads

Worker Fundamentals

Basic Worker Structure

// src/index.ts
export interface Env {
  MEETING_CACHE: KVNamespace;
  RATE_LIMIT: KVNamespace;
  API_KEY: string;
}

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

    // CORS handling
    if (request.method === 'OPTIONS') {
      return handleCORS();
    }

    try {
      // Route handling
      if (url.pathname === '/health') {
        return json({ status: 'ok' });
      }

      if (url.pathname.startsWith('/api/')) {
        return handleAPI(request, env, ctx);
      }

      return new Response('Not Found', { status: 404 });
    } catch (error) {
      console.error('Worker error:', error);
      return json({ error: 'Internal error' }, 500);
    }
  },

  // Cron trigger
  async scheduled(event: ScheduledEvent, env: Env, ctx: ExecutionContext) {
    ctx.waitUntil(runScheduledTask(env));
  }
};

CORS Headers (Essential)

const CORS_HEADERS = {
  'Access-Control-Allow-Origin': '*', // Or specific origin
  'Access-Control-Allow-Methods': 'GET, POST, PUT, DELETE, OPTIONS',
  'Access-Control-Allow-Headers': 'Content-Type, Authorization',
  'Access-Control-Max-Age': '86400',
};

function handleCORS(): Response {
  return new Response(null, { status: 204, headers: CORS_HEADERS });
}

function json(data: unknown, status = 200): Response {
  return new Response(JSON.stringify(data), {
    status,
    headers: {
      ...CORS_HEADERS,
      'Content-Type': 'application/json',
    },
  });
}