Why does my activity monitor show Node.js using multiple threads?

Question

I opened my activity monitory in OSX to to see how Node was getting along and to my surprise it's using 8 threads. How can in be!!?

Answer 1

Node.js is single-threaded.

However, it is built on libuv which handles all low-level platform-dependent stuff, including async IO.

Now the issue is that there is no good API for async IO in operating systems nowadays. Different APIs exist, but they all have their issues.

So in order to implement cross-platform async API, libuv emulates it using a thread pool. This is where those threads are coming from.