#API

Stop fighting CORS. Understand preflight requests, credentials, wildcard mistakes. CORS isn't a bug—it's your API warning you about real security issues.

A slow MongoDB + Node.js API was taking 15 minutes to return 8,000 records. Here's the exact process I used to diagnose it — missing indexes, in-memory aggregation, no pagination — and bring it down to 15 seconds.

You cast the API response to `any` to stop TypeScript complaining. It worked. Now a field changed shape three months later and the bug is in production. Here's how to type messy API responses properly — with real validation, not just type assertions.