How can Node handle many requests with one JavaScript thread?

Definition:

Node.js is a JavaScript runtime designed to handle many operations that spend time waiting for I/O. It lets the operating system and supporting runtime facilities wait for work, then runs ready JavaScript callbacks on an event-loop thread. This makes one process useful for many concurrent connections without one JavaScript thread per request.

Key points:

• Network I/O waits outside the JavaScript thread using the OS and libuv.

• The event loop runs callbacks when work is ready.

• Heavy synchronous work still blocks other requests on that thread.

• Concurrency means multiple requests are in progress; it does not mean their JavaScript runs simultaneously on the same thread.

Interview point:

• Describe what happens while a database request waits, and contrast that with a CPU-heavy loop occupying the thread.