Node.js Lesson: Internals of Nodejs: Event Loop

This Node.js lesson will continue the last lesson where we learned how the LibUV library works internally. We will learn about Event Loop and understand various terms like call stack, callback queue, etc. Let’s start.

Hey everyone, this lesson will continue the last lesson where we learned how the LibUV library works internally. In this lesson, we will learn about Event Loop and understand various terms like call stack, callback queue, etc. Let’s start.

What is Call Stack

JavaScript is a single-threaded language, which means it can do one thing at a time. This also means that it has a single Call Stack. Now, what is a Call Stack?

A call stack is a data structure that holds information about what line of the function is currently being executed. A call stack is used to keep method calls, and it follows the LIFO (Last In First Out) data structure. By LIFO, we mean a container where the last item entered will be the first to get out. There is only one entry from the top, and if you want to take the item at the end, you will have to take everything on top first. If you’re thinking about a box of Pringles, then you’re absolutely correct.

Let’s understand how this call stack holds method calls:

Callback excallidraw example

The execution will go on like this:

1. We call the main() function, it gets pushed into the call stack.
2. This will call the add() function and push it to call stack.
3. Once it hit return, add() will be popped out from the call stack.
4. Finally, the main() will be popped out.

node nodejs javascript programming

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