Search⌘ K
Home
Courses
Learn Node.js

Under the Hood of Asynchronous Execution

Explore the key components behind asynchronous execution in Node.js, including the call stack, libuv, callback queues, and the event loop. Understand how these work together to handle functions like setTimeout efficiently, enabling non-blocking, scalable back-end applications.

We'll cover the following...

In previous lessons, we introduced asynchronous programming. Now, we’ll go under the hood to see how Node.js handles asynchronous tasks with the event loop, libuv, and the callback queue. Understanding these components helps us write efficient, non-blocking code.

Core components of asynchronous execution

When Node.js runs a file with both synchronous and asynchronous code, it coordinates execution using the following four components.:

  1. Call stack: The primary space where JavaScript code runs, handling synchronous tasks—such as variable declarations or console.log statements—immediately in the order they appear in the code. If a piece of code calls a function, that function is added to the top of the call stack. Once the function finishes executing, it is removed from the stack. For asynchronous functions like setTimeout, Node.js initially adds them to the call stack, but instead of waiting there, they hand off control to libuv.

  2. libuv and Timer API: Node.js uses libuv, a library that manages various asynchronous ...