Understanding Asynchronous JavaScript: Callbacks, Promises, and Async/Await

JavaScript is single-threaded, meaning it executes one operation at a time. However, real-world applications require handling multiple tasks concurrently, such as fetching data from an API, reading files, or querying a database. Asynchronous JavaScript enables non-blocking operations, improving performance and responsiveness.

In this article, we’ll explore three main ways to handle asynchronous operations: Callbacks, Promises, and Async/Await.

1. Understanding Synchronous vs Asynchronous JavaScript

Synchronous Code (Blocking)

JavaScript executes one line at a time. If a task takes too long (e.g., reading a file), the entire script is blocked.
Example:

console.log("Start");
for (let i = 0; i < 1000000000; i++) {} // Simulating a long task
console.log("End");

In this case, JavaScript waits for the loop to complete before moving to the next line.

Asynchronous Code (Non-Blocking)

JavaScript uses the Event Loop and callback queue to handle asynchronous operations efficiently.
Example: