How do I fix CORS error in JavaScript?

Ah yes. CORS. The browser’s way of saying:
"I don’t trust your janky localhost Express server."

Solutions:

Backend: Set the right Access-Control-Allow-Origin header.

Frontend: Cry.

Dev mode: Disable CORS and pretend security isn't real. YOLO.

Just know — even when you fix it, Chrome remembers.
It always remembers.