40/60 Days System Design Questions (opens in new tab)

Your React dashboard freezes for 4 seconds every time a user uploads a CSV. Not a network freeze. A browser freeze. Tab unresponsive. Animations stuck. The "Page Unresponsive" dialog popping up on Chrome. Here's what's happening in prod: • User drops a 80MB CSV (200k rows, 40 columns) into the upload zone • Your code: Papa.parse(file, { complete: ... }) on the main thread • Parsing + validation + schema mapping = 3.8s of synchronous JS • During those 3.8s: scroll dies, the loading spinner sto...