javascript v8 engine

Brief Description About The V8 JavaScript Engine

V8 is the name of the JavaScript engine that powers Google Chrome. It’s the thing that takes our JavaScript and executes it while browsing with Chrome.


V8 provides the runtime environment in which JavaScript executes. The DOM, and the other Web Platform APIs are provided by the browser.

The cool thing is that the JavaScript engine is independent by the browser in which it’s hosted. This key feature enabled the rise of Node.js. V8 was chosen for being the engine chosen by Node.js back in 2009, and as the popularity of Node.js exploded, V8 became the engine that now powers an incredible amount of server-side code written in JavaScript.

The Node.js ecosystem is huge and thanks to it V8 also powers desktop apps, with projects like Electron.

Other JS engines

Other browsers have their own JavaScript engine:

  • Firefox has Spidermonkey
  • Safari has JavaScriptCore (also called Nitro)
  • Edge has Chakra

and many others exist as well.

All those engines implement the ECMA ES-262 standard, also called ECMAScript, the standard used by JavaScript.


The Chrome V8 engine :

  • The V8 engine is written in C++ and used in Chrome and Nodejs.
  • It implements ECMAScript as specified in ECMA-262.
  • The V8 engine can run standalone we can embed it with our own C++ program.

Let us understand the last point a little better. V8 can run standalone and at the same time we can add our own function implementation in C++ to add new features to JavaScript.

So for example: print('hello world')is not a valid statement in Node.js. It will give error if we compile it. But we can add our own implementation of the print function in C++ on top of the V8 which is open source at Github, thus making the print function work natively. This allows the JavaScript to understand more than what the ECMAScript standard specifies the JavaScript should understand.

javascript v8 engine

This is a powerful feature since C++ has more features as a programming language as compared to JavaScript, as it is much closer to hardware like dealing with files and folders on the hard drive.

Allowing us to write code in C++ and making it available to JavaScript makes it so we can add more features to JavaScript.

Node.js in itself is a C++ implementation of a V8 engine allowing server side programming and networking applications.

Let’s now look at some of the open source code inside the engine. To do this, you need to go to the v8/samples/ folder .

Here you can see the implementation of different functions such as Print and Read, which are natively not available in Node.js.


The quest for performance

V8 is written in C++, and it’s continuously improved. It is portable and runs on Mac, Windows, Linux and several other systems.

In this V8 introduction, I will ignore the implementation details of V8: they can be found on more authoritative sites (e.g. the V8 official site), and they change over time, often radically.

V8 is always evolving, just like the other JavaScript engines around, to speed up the Web and the Node.js ecosystem.

On the web, there is a race for performance that’s been going on for years, and we (as users and developers) benefit a lot from this competition because we get faster and more optimized machines year after year.


JavaScript is generally considered an interpreted language, but modern JavaScript engines no longer just interpret JavaScript, they compile it.

This happens since 2009 when the SpiderMonkey JavaScript compiler was added to Firefox 3.5, and everyone followed this idea.

JavScript is internally compiled by V8 with just-in-time (JIT) compilation to speed up the execution.

This might seem counter-intuitive, but since the introduction of Google Maps in 2004, JavaScript has evolved from a language that was generally executing a few dozens of lines of code to complete applications with thousands to hundreds of thousands of lines running in the browser.

Our applications now can run for hours inside a browser, rather than being just a few form validation rules or simple scripts.

In this new world, compiling JavaScript makes perfect sense because while it might take a little bit more to have the JavaScript ready, once done it’s going to be much more performant that purely interpreted code.

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