20 Mistakes That Quietly Destroy JavaScript/TypeScript Codebases (Part 2)

Runtime bugs don't break your build — they break production at 3am. This deep-dive covers memory leaks from uncleared intervals and event listeners, missing AbortController cancellation, fetch requests with no timeouts, blocking the Node.js event loop with sync operations, timezone pitfalls with Date, and input validation gaps that enable mass assignment attacks. Practical fixes with real code patterns throughout.