How JavaScript Works Behind the Scenes: Explained with Simple Examples

If you’re learning JavaScript, you’ve probably wondered what’s really happening when your code runs. What does the browser do with your console.log()? How does JavaScript know what to execute — and when? This post will break it all down in a simple way.

We’ll answer the big question: How JavaScript works behind the scenes

What Is JavaScript?

JavaScript is a high-level, interpreted programming language. It’s mostly used in web development to add interactivity — like animations, popups, and dynamic content — to websites.

It runs in the browser (like Chrome or Firefox) using something called a JavaScript engine. Every major browser has its own engine:

• Chrome uses V8
• Firefox uses SpiderMonkey
• Safari uses JavaScriptCore

JavaScript Is Single-Threaded

This is one of the most important things to understand.

JavaScript can only do one thing at a time. That’s what “single-threaded” means.

Think of it like a to-do list. JavaScript goes through it from top to bottom, step by step. If one item takes a while, the rest have to wait. This is why…