Interview Questions

JS runs on a single thread with a call stack. Async callbacks go to task queues (macrotasks like setTimeout, microtasks like Promises). The event loop pushes queued callbacks onto the stack only when it is empty, draining all microtasks before the next macrotask.

Generate a unique short code (base62 of an auto-increment ID or a hash) mapping to the long URL in a key-value/relational store. Add caching (Redis) for hot reads, a redirect service returning 301/302, analytics, and consider sharding + a counter service for scale.