1# Workers Playground Gotchas
2 
3## Platform Limitations
4 
5| Limitation | Impact | Workaround |
6|------------|--------|------------|
7| Safari broken | Preview fails | Use Chrome/Firefox/Edge |
8| TypeScript unsupported | TS syntax errors | Write plain JS or use JSDoc |
9| No bindings | `env` always `{}` | Mock data or use external APIs |
10| No env vars | Can't access secrets | Hardcode for testing |
11 
12## Common Runtime Errors
13 
14### "Response body already read"
15 
16```javascript
17// ❌ Body consumed twice
18const body = await request.text();
19await fetch(url, { body: request.body }); // Error!
20 
21// ✅ Clone first
22const clone = request.clone();
23const body = await request.text();
24await fetch(url, { body: clone.body });
25```
26 
27### "Worker exceeded CPU time"
28 
29**Limit:** 10ms (free), 30s default / 5min max (paid)
30 
31```javascript
32// ✅ Move slow work to background
33ctx.waitUntil(fetch('https://analytics.example.com', {...}));
34return new Response('OK'); // Return immediately
35```
36 
37### "Too many subrequests"
38 
39**Limit:** 50 (free), 1000 (paid)
40 
41```javascript
42// ❌ 100 individual fetches
43// ✅ Batch into single API call
44await fetch('https://api.example.com/batch', {
45  body: JSON.stringify({ ids: [...] })
46});
47```
48 
49## Best Practices
50 
51```javascript
52// Clone before caching
53await cache.put(request, response.clone());
54return response;
55 
56// Validate input early
57if (request.method !== 'POST') return new Response('', { status: 405 });
58 
59// Handle errors
60try { ... } catch (e) {
61  return Response.json({ error: e.message }, { status: 500 });
62}
63```
64 
65## Limits
66 
67| Resource | Free | Paid |
68|----------|------|------|
69| CPU time | 10ms | 30s (default), 5min (max) |
70| Memory | 128 MB | 128 MB |
71| Subrequests | 50 | 10,000 |
72 
73## Browser Support
74 
75| Browser | Status |
76|---------|--------|
77| Chrome | ✅ Recommended |
78| Firefox | ✅ Works |
79| Edge | ✅ Works |
80| Safari | ❌ Broken |
81 
82## Debugging
83 
84```javascript
85console.log('URL:', request.url); // View in browser DevTools Console
86```
87 
88**Note:** `console.log` works in playground. For production, use Logpush or Tail Workers.
89