1# Workers Playground API
2 
3## Handler
4 
5```javascript
6export default {
7  async fetch(request, env, ctx) {
8    // request: Request, env: {} (empty in playground), ctx: ExecutionContext
9    return new Response('Hello');
10  }
11};
12```
13 
14## Request
15 
16```javascript
17const method = request.method;       // "GET", "POST"
18const url = new URL(request.url);    // Parse URL
19const headers = request.headers;     // Headers object
20const body = await request.json();   // Read body (consumes stream)
21const clone = request.clone();       // Clone before reading body
22 
23// Query params
24url.searchParams.get('page');        // Single value
25url.searchParams.getAll('tag');      // Array
26 
27// Cloudflare metadata
28request.cf.country;                  // "US"
29request.cf.colo;                     // "SFO"
30```
31 
32## Response
33 
34```javascript
35// Text
36return new Response('Hello', { status: 200 });
37 
38// JSON
39return Response.json({ data }, { status: 200, headers: {...} });
40 
41// Redirect
42return Response.redirect('/new-path', 301);
43 
44// Modify existing
45const modified = new Response(response.body, response);
46modified.headers.set('X-Custom', 'value');
47```
48 
49## ExecutionContext
50 
51```javascript
52// Background work (after response sent)
53ctx.waitUntil(fetch('https://logs.example.com', { method: 'POST', body: '...' }));
54return new Response('OK'); // Returns immediately
55```
56 
57## Fetch
58 
59```javascript
60const response = await fetch('https://api.example.com');
61const data = await response.json();
62 
63// With options
64await fetch(url, {
65  method: 'POST',
66  headers: { 'Content-Type': 'application/json' },
67  body: JSON.stringify({ name: 'Alice' })
68});
69```
70 
71## Cache
72 
73```javascript
74const cache = caches.default;
75 
76// Check cache
77let response = await cache.match(request);
78if (!response) {
79  response = await fetch(origin);
80  await cache.put(request, response.clone()); // Clone before put!
81}
82return response;
83```
84 
85## Crypto
86 
87```javascript
88crypto.randomUUID();                 // UUID v4
89crypto.getRandomValues(new Uint8Array(16));
90 
91// SHA-256 hash
92const hash = await crypto.subtle.digest('SHA-256', new TextEncoder().encode(data));
93```
94 
95## Limits (Playground = Free Plan)
96 
97| Resource | Limit |
98|----------|-------|
99| CPU time | 10ms (Free plan; Paid: 30s default, 5min max) |
100| Subrequests | 50 |
101| Memory | 128 MB |
102