Skillintermediate

Workers Playground Gotchas

| Limitation | Impact | Workaround | |------------|--------|------------| | Safari broken | Preview fails | Use Chrome/Firefox/Edge | | TypeScript unsupported | TS syntax errors | Write plain JS or use JSDoc | | No bindings | `env` always `{}` | Mock data or use external APIs | | No env vars | Can't access secrets | Hardcode for testing |

Claude Code Knowledge Pack7/10/2026

Overview

Workers Playground Gotchas

Platform Limitations

Limitation	Impact	Workaround
Safari broken	Preview fails	Use Chrome/Firefox/Edge
TypeScript unsupported	TS syntax errors	Write plain JS or use JSDoc
No bindings	`env` always `{}`	Mock data or use external APIs
No env vars	Can't access secrets	Hardcode for testing

Common Runtime Errors

"Response body already read"

// ❌ Body consumed twice
const body = await request.text();
await fetch(url, { body: request.body }); // Error!

// ✅ Clone first
const clone = request.clone();
const body = await request.text();
await fetch(url, { body: clone.body });

"Worker exceeded CPU time"

Limit: 10ms (free), 50ms (paid)

// ✅ Move slow work to background
ctx.waitUntil(fetch('https://analytics.example.com', {...}));
return new Response('OK'); // Return immediately

"Too many subrequests"

Limit: 50 (free), 1000 (paid)

// ❌ 100 individual fetches
// ✅ Batch into single API call
await fetch('https://api.example.com/batch', {
  body: JSON.stringify({ ids: [...] })
});

Best Practices

// Clone before caching
await cache.put(request, response.clone());
return response;

// Validate input early
if (request.method !== 'POST') return new Response('', { status: 405 });

// Handle errors
try { ... } catch (e) {
  return Response.json({ error: e.message }, { status: 500 });
}

Limits

Resource	Free	Paid
CPU time	10ms	50ms
Memory	128 MB	128 MB
Subrequests	50	10,000

Browser Support

Browser	Status
Chrome	✅ Recommended
Firefox	✅ Works
Edge	✅ Works
Safari	❌ Broken

Debugging

console.log('URL:', request.url); // View in browser DevTools Console

Note: console.log works in playground. For production, use Logpush or Tail Workers.