How Does JavaScript Work Behind the Scenes? JS Engine and Runtime Explained

So you may know that your code somehow compiles and executes in your browser to display the beautiful web application you’ve built. But are you aware of all the components that come into play to enable the output? 

Let’s dive a little into JavaScript behind the scenes. The abstract part that you can’t exactly see.

Why should a seemingly abstract subject matter to you? An understanding of the inner workings of JavaScript allows you to explore the language beyond the surface level and from a deeper perspective.

It provides contextual information on the language and how the JavaScript engine optimizes code. This will give you some important foundational knowledge which shapes the way you write code. It also helps you write more efficient, scalable, and maintainable code.

The JavaScript Engine

JavaScript Engine showing the Call stack and the Heap

The JavaScript engine is simply a computer program that interprets JavaScript code. The engine is responsible for executing the code.

Every major browser has a JavaScript engine that executes JavaScript code. The most popular one is the Google Chrome V8 engine. Google’s V8 powers Google Chrome and Node.js, a back-end JavaScript runtime environment used to build server-side applications.

Other major browser engines include:

• SpiderMonkey developed by Mozilla for Firefox
• JavaScriptCore which powers the Safari browser
• Chakra which powers Internet Explorer