event-loop

Threads are not the only model for concurrency. Learn how blocking vs non-blocking I/O works, how the event loop and reactor pattern scale to millions of connections, and how callbacks evolved into futures, promises, and async/await — plus where coroutines fit and when async loses to threads.

How Node 22 actually runs your code: V8, the libuv event loop and its phases, microtasks vs macrotasks, blocking pitfalls, and where worker threads, npm, pnpm, and bun fit in 2026.