# Workers Playground API

## Handler

```javascript
export default {
  async fetch(request, env, ctx) {
    // request: Request, env: {} (empty in playground), ctx: ExecutionContext
    return new Response('Hello')
  },
}
```

## Request

```javascript
const method = request.method // "GET", "POST"
const url = new URL(request.url) // Parse URL
const headers = request.headers // Headers object
const body = await request.json() // Read body (consumes stream)
const clone = request.clone() // Clone before reading body

// Query params
url.searchParams.get('page') // Single value
url.searchParams.getAll('tag') // Array

// Cloudflare metadata
request.cf.country // "US"
request.cf.colo // "SFO"
```

## Response

```javascript
// Text
return new Response('Hello', { status: 200 });

// JSON
return Response.json({ data }, { status: 200, headers: {...} });

// Redirect
return Response.redirect('/new-path', 301);

// Modify existing
const modified = new Response(response.body, response);
modified.headers.set('X-Custom', 'value');
```

## ExecutionContext

```javascript
// Background work (after response sent)
ctx.waitUntil(fetch('https://logs.example.com', { method: 'POST', body: '...' }))
return new Response('OK') // Returns immediately
```

## Fetch

```javascript
const response = await fetch('https://api.example.com')
const data = await response.json()

// With options
await fetch(url, {
  method: 'POST',
  headers: { 'Content-Type': 'application/json' },
  body: JSON.stringify({ name: 'Alice' }),
})
```

## Cache

```javascript
const cache = caches.default

// Check cache
let response = await cache.match(request)
if (!response) {
  response = await fetch(origin)
  await cache.put(request, response.clone()) // Clone before put!
}
return response
```

## Crypto

```javascript
crypto.randomUUID() // UUID v4
crypto.getRandomValues(new Uint8Array(16))

// SHA-256 hash
const hash = await crypto.subtle.digest('SHA-256', new TextEncoder().encode(data))
```

## Limits (Playground = Free Plan)

| Resource    | Limit  |
| ----------- | ------ |
| CPU time    | 10ms   |
| Subrequests | 50     |
| Memory      | 128 MB |
