Does Node.js actually use multiple threads underneath?

Question

After all the literature i've read on node.js I still come back to the question, does node.js itself make use of multiple threads under the hood? I think the answer is yes because if we use the simple asynch file read example something has to be doing the work to read the file but if the main event loop of node is not processing this work than that must mean there should be a POSIX thread running somewhere that takes care of the file reading and then upon completion places the call back in the event loop to be executed. So when we say Node.js runs in one thread do we actually mean that the event loop of node.js is only one thread? Or am i missing something here.....

Answer 1

To a Javascript program on node.js, there is only one thread.

If you're looking for technicalities, node.js is free to use threads to solve asynchronous I/O if the underlying operating system requires it.

The important thing is to never break the "there is only one thread" abstraction to the Javascript program. If there are more threads, all they can do is queue up work for the main thread in the Javascript program, they can never execute any Javascript code themselves.