Instances where Node.js operations need to be synchronous

JavaScript is single-threaded (besides web workers and spawning multiple processes), and it's best not to wait for long-running operations as it blocks the thread. But still, when taking a peek into several modules in Github, they actually use these syncrhonous operations, most of the time in file operations.

Am I staring at bad code/practice? Or is there some real need for synchronous operations in JavaScript that I am not aware of?

Can you post an example? You are most likely looking at:

  • a call that is actually asynchronous such as fs.read. Note that all synchronous calls in the node core API end with the word "Sync" like fs.readSync.
  • synchronous code such as require('somemodule') that runs before the application begins accepting network requests

And yes, if you are seeing code doing something like fs.readSync while responding to an HTTP request, that is bad code/practice and that application will lock up while that synchronous operation happens.

Node.js it's not single-threaded, uses a pool of threads but they are exposed as a single thread to the javascript layer, otherwise would be impossible to write asynchronous code. Any I/O call blocks the current thread.

Threads are used internally to fake the asynchronous nature of all the system calls. libuv also uses threads to allow you, the application, to perform a task asynchronously that is actually blocking, by spawning a thread and collecting the result when it is done.

http://nikhilm.github.com/uvbook/threads.html

Node.js has decided to include synchronous functions to maintain a similitude with other common languages, but they shouldn't be used, never, never, never!

Node.js in its nature is asynchronous, it's pure javascript. Javascript is synonym of closure, of callback. If you want to write synchronous code with Node.js perhaps you should try another scripting language like python.

There's an excellent module called async that eases the pain of nested callbacks. Then, why should I use synchronous code? Silly. If I use synchronous code I lose all the benefits that Node provides to me. The only exception are CLI apps, but again, I'll prefer to write all the code asynchronously. It's not really hard.

At some level, a synchronous operation has to occur. Node.js puts those in threads so that the whole server isn't blocked.