# Cloudflare Workers

Expert guidance for building, deploying, and optimizing Cloudflare Workers applications.

## Overview

Cloudflare Workers run on V8 isolates (NOT containers/VMs):
- Extremely fast cold starts (< 1ms)
- Global deployment across 300+ locations
- Web standards compliant (fetch, URL, Headers, Request, Response)
- Support JS/TS, Python, Rust, and WebAssembly

**Key principle**: Workers use web platform APIs wherever possible for portability.

## Module Worker Pattern (Recommended)

```typescript
export default {
  async fetch(request: Request, env: Env, ctx: ExecutionContext): Promise<Response> {
    return new Response('Hello World!');
  },
};
```

**Handler parameters**:
- `request`: Incoming HTTP request (standard Request object)
- `env`: Environment bindings (KV, D1, R2, secrets, vars)
- `ctx`: Execution context (`waitUntil`, `passThroughOnException`)

## Essential Commands

```bash
npx wrangler dev                    # Local dev
npx wrangler dev --remote           # Remote dev (actual resources)
npx wrangler deploy                 # Production
npx wrangler deploy --env staging   # Specific environment
npx wrangler tail                   # Stream logs
npx wrangler secret put API_KEY     # Set secret
```

## When to Use Workers

- API endpoints at the edge
- Request/response transformation
- Authentication/authorization layers
- Static asset optimization
- A/B testing and feature flags
- Rate limiting and security
- Proxy/routing logic
- WebSocket applications

## Quick Start

```bash
npm create cloudflare@latest my-worker -- --type hello-world
cd my-worker
npx wrangler dev
```

## Handler Signatures

```typescript
// HTTP requests
async fetch(request: Request, env: Env, ctx: ExecutionContext): Promise<Response>

// Cron triggers
async scheduled(event: ScheduledEvent, env: Env, ctx: ExecutionContext): Promise<void>

// Queue consumer
async queue(batch: MessageBatch, env: Env, ctx: ExecutionContext): Promise<void>

// Tail consumer
async tail(events: TraceItem[], env: Env, ctx: ExecutionContext): Promise<void>
```

## Resources

**Docs**: https://developers.cloudflare.com/workers/  
**Examples**: https://developers.cloudflare.com/workers/examples/  
**Runtime APIs**: https://developers.cloudflare.com/workers/runtime-apis/

## In This Reference

- [Configuration](./configuration.md) - wrangler.jsonc setup, bindings, environments
- [API](./api.md) - Runtime APIs, bindings, execution context
- [Patterns](./patterns.md) - Common workflows, testing, optimization
- [Gotchas](./gotchas.md) - Common issues, limits, troubleshooting

## See Also

- [KV](../kv/README.md) - Key-value storage
- [D1](../d1/README.md) - SQL database
- [R2](../r2/README.md) - Object storage
- [Durable Objects](../durable-objects/README.md) - Stateful coordination
- [Queues](../queues/README.md) - Message queues
- [Wrangler](../wrangler/README.md) - CLI tool reference
