The Responsibility of the Node.js Event Loop

Everyone always talks about the Node.js event loop and how its important, but what exactly is it responsible for?

Well… Let’s take a look! 😀

The event loop (event queue) in Node.js is a loop that is responsible for processesing incoming requests. This loop “contains” a queue of requests, and each request in the event loop is a callback.


Node.js Event Loop

The Node.js Event Loop

Since the Node.js event loop contains a queue, it processes the requests like a traditional queue First-In-First-Out (FIFO) fashion. Node.js will continue processing each callback in the event loop until there are no more callbacks left to process.


In order to do this, Node.js registers with the Operating System. When an request arrives, Node.js is alerted, and the event loop processes the request. Any other subsequent connections that are made are queued until Node.js has finished with the current request.


The event loop allows Node.js to scale efficiently by accepting (queueing) many requests at once. Efficient scaling is one of the benefits that Node.js (with the event loop) has over traditional web servers. The event loop is single-threaded. This allows Node.js (when used properly) to require far less computational resources than traditional web servers.

Traditional web servers like Apache or Nginx are multi-threaded. Multi-threaded web servers typically cannot scale to the magnitude that Node.js can without greatly increasing the system’s computing resources. Since multi-threaded web servers create a new thread for each incoming request, this increases both CPU and RAM requirements of the system for the same amount of traffic. This increase can be either positive or negative (depending on your application), but the amount of computing resources for multi-threaded web servers will be greater than the requirement for single-threaded ones.


And that’s it on the Node.js event loop for now!

Happy coding! 😀

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