JavaScript Event Loop Explained with Simple Examples

Introduction

JavaScript is single-threaded, yet it can handle asynchronous operations efficiently. This is possible because of the event loop.

In this article, we’ll break down the JavaScript event loop in a simple and easy-to-understand way.

Being single-threaded means JavaScript can execute only one piece of code at a time.

To manage multiple tasks like API calls and timers, JavaScript relies on the event loop.

The call stack keeps track of function execution.


function first() {
  second();
}

function second() {
  console.log("Hello");
}

first();

Functions are added to the stack when called and removed when completed.

Async operations are handled by Web APIs, and their callbacks are pushed to the callback queue.

The event loop constantly checks if the call stack is empty. If it is, it moves callbacks from the queue to the stack.

Understanding the event loop helps you debug async issues and write better JavaScript code.