Concurrency vs. Parallelism in JavaScript: Understanding the Difference

Introduction

If you’ve worked with JavaScript for a while, you’ve probably heard terms like concurrency and parallelism tossed around. Maybe you’ve wondered, “Are they the same thing?” or “Why does JavaScript handle concurrency so well if it’s single-threaded?” Understanding these concepts is essential for writing efficient and performant code, especially in modern web development.

In this article, we’ll demystify concurrency and parallelism, explore how they relate to JavaScript’s event loop and multithreading, and provide beginner-friendly examples to solidify your understanding. By the end, you’ll know how to handle tasks concurrently in JavaScript and understand the difference between concurrency and parallelism.

What Are Concurrency and Parallelism?

Concurrency

Concurrency refers to the ability to handle multiple tasks at the same time. However, these tasks don’t necessarily run simultaneously. Instead, they progress in small chunks, sharing resources like a single CPU core.

Think of a single waiter managing multiple tables at a restaurant. The waiter can attend to multiple customers by switching between them, but only handles one request at a time.