# Browser Rendering Patterns

## Basic Worker

```typescript
import puppeteer from '@cloudflare/puppeteer'

export default {
  async fetch(request, env) {
    const browser = await puppeteer.launch(env.MYBROWSER)
    try {
      const page = await browser.newPage()
      await page.goto('https://example.com')
      return new Response(await page.content())
    } finally {
      await browser.close() // ALWAYS in finally
    }
  },
}
```

## Session Reuse

Keep sessions alive for performance:

```typescript
let sessionId = await env.SESSION_KV.get('browser-session')
if (sessionId) {
  browser = await puppeteer.connect(env.MYBROWSER, sessionId)
} else {
  browser = await puppeteer.launch(env.MYBROWSER, { keep_alive: 600000 })
  await env.SESSION_KV.put('browser-session', browser.sessionId(), { expirationTtl: 600 })
}
// Don't close browser to keep session alive
```

## Common Operations

| Task         | Code                                                                  |
| ------------ | --------------------------------------------------------------------- |
| Screenshot   | `await page.screenshot({ type: "png", fullPage: true })`              |
| PDF          | `await page.pdf({ format: "A4", printBackground: true })`             |
| Extract data | `await page.evaluate(() => document.querySelector('h1').textContent)` |
| Fill form    | `await page.type('#input', 'value'); await page.click('button')`      |
| Wait nav     | `await Promise.all([page.waitForNavigation(), page.click('a')])`      |

## Parallel Scraping

```typescript
const pages = await Promise.all(urls.map(() => browser.newPage()))
await Promise.all(pages.map((p, i) => p.goto(urls[i])))
const titles = await Promise.all(pages.map((p) => p.title()))
```

## Playwright Selectors

```typescript
import { launch } from '@cloudflare/playwright'
const browser = await launch(env.MYBROWSER)
await page.getByRole('button', { name: 'Sign in' }).click()
await page.getByLabel('Email').fill('user@example.com')
await page.getByTestId('submit-button').click()
```

## Incognito Contexts

Isolated sessions without multiple browsers:

```typescript
const ctx1 = await browser.createIncognitoBrowserContext()
const ctx2 = await browser.createIncognitoBrowserContext()
// Each has isolated cookies/storage
```

## Quota Check

```typescript
const limits = await puppeteer.limits(env.MYBROWSER)
if (limits.remaining < 60000) return new Response('Quota low', { status: 429 })
```

## Error Handling

```typescript
try {
  await page.goto(url, { timeout: 30000, waitUntil: 'networkidle0' })
} catch (e) {
  if (e.message.includes('timeout')) return new Response('Timeout', { status: 504 })
  if (e.message.includes('Session limit')) return new Response('Too many sessions', { status: 429 })
} finally {
  if (browser) await browser.close()
}
```