JavaScript - Asynchronous Overview

Overview

Estimated time: 20–30 minutes

JavaScript is single-threaded but can handle asynchronous operations using callbacks, promises, and async/await. Understanding async code is essential for working with timers, network requests, and UI events.

Learning Objectives

• Understand the event loop and async execution.
• Use callbacks, promises, and async/await.

Prerequisites

• JavaScript - History & Versions

Callbacks

setTimeout(function() {
  console.log('Hello after 1 second');
}, 1000);

Promises

const p = new Promise((resolve) => setTimeout(() => resolve(42), 500));
p.then(value => console.log(value));

Async/Await

async function getData() {
  const value = await p;
  console.log(value);
}
getData();

Event Loop

The event loop allows JavaScript to handle async tasks by queuing callbacks and running them after the current code finishes.

Common Pitfalls

• Forgetting to handle errors in async code.
• Callback hell: deeply nested callbacks are hard to read and maintain.

Summary

Asynchronous programming is key to responsive JavaScript apps. Use promises and async/await for cleaner, more maintainable code.