V8

Have you ever been interested in how your code, written in high-level language like TypeScript, transforms into a different representation that a computer can understand, a CPU can understand?

I hope, when you will read this article, the picture of code execution pipeline will be more explicit. We will trace the journey of the code, starting from high-level language to low-level machine instructions. We are going to a deep rabbit hole…

DISCLAIMER: I will not dive into technical details of implementation, which differs from one vendor to another. We will go through a conceptual overview only. Otherwise, the article would take hours to read and months to write.

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Recently, I find out about a strange bug in V8. Everyone is discussing it in Twitter, Facebook, Gitter and other social networks. So, I will try to explain it.

To my knowledge, it happens in the latest stable version of Google Chrome (my version is 51.0.2704.103).

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Last time, I showed you how to profile your application and find the place which slows it down — bottleneck. It helps a lot with finding the place in the code that executes slow, so you can fix that.

But, what if you don’t know how to fix that? How to find the reason for de-optimization in your JavaScript code when you have a lot of different variants of that de-optimization. How to trace specific de-optimizations in your code?

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In my previous article, I was talking about Node.js and why it’s fast. Today, I want to talk about V8.

I suppose some of you heard that JavaScript executes as fast as C++. Some of you don’t understand how it’s even possible. JavaScript is a dynamically typed language with Just in Time (JIT) compilation, when C++ is static-typed language with Ahead of Time (AoT) compilation. And somehow, optimised JavaScript code executes a little slower than C++ or even with the same speed.

To understand why that is, you need to know some basics of V8 implementation. It’s a huge topic, so I will only explain key features of V8 in this post. If you want more details, such as hidden classes, SSA, IC,… they will be in my next article.

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Here I am again with an article about Node.js! Today I want to speak about another Node.js advantage — execution speed. What do I mean by “execution speed”?

It can be anything ranging from calculating Fibonacci sequence to querying database.

When talking about web-services, execution speed comprises everything that is needed to process requests and send the response to the client. That’s what I mean — time spent on processing request, starting from opening connection to client receiving the response.

As soon as you understand what’s going on in Node.js server when it processes the requests, you will realise why it is so fast.

But before talking about Node.js, let’s look at how request handling is done in other languages. PHP is the best example because it is popular and unoptimised.

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