What are the most common mistakes in Node.js web scraping?

1. Not handling errors properly:

Network failures, timeouts, and unexpected HTML structures cause crashes. Always use try-catch blocks and handle specific error types.

2. Forgetting to set headers:

Missing or default User-Agent headers get blocked. Always set realistic browser headers.

3. Making too many concurrent requests:

Overwhelming servers triggers rate limiting and IP bans. Use concurrency limits (3-5 requests) and delays between requests.

4. Not handling relative URLs:

Links like /about need to be converted to absolute URLs using the base domain.

5. Parsing dynamic content with Cheerio:

JavaScript-rendered content won't appear in the HTML that Cheerio parses. Use Puppeteer for these sites.

6. Ignoring robots.txt:

Scraping disallowed pages can lead to legal issues and IP bans. Always check and respect robots.txt.

7. Not implementing retries:

Temporary network issues cause unnecessary failures. Implement exponential backoff retry logic.

8. Memory leaks with Puppeteer:

Not closing browser instances leads to memory exhaustion. Always close browsers in finally blocks.

9. Synchronous scraping:

Sequential requests are slow. Use Promise.all() or async iteration with concurrency control.

10. Not handling pagination:

Missing pagination logic means incomplete data. Implement proper next-page detection and following.

11. Hardcoding selectors:

Selectors break when sites update. Make selectors configurable and add fallbacks.

12. Not validating scraped data:

Parsing errors produce garbage data. Validate extracted data before saving.

13. Ignoring rate limits:

Hitting sites too fast triggers blocks. Implement delays and respect Retry-After headers.

14. Not using proxies for scale:

Single IP scraping gets blocked quickly. Rotate proxies for large-scale scraping.

15. Logging sensitive data:

Logging full responses includes API keys and tokens. Sanitize logs to remove sensitive data.