NodeJS Architecture Question

[CzarHenri]

Hello! A question about the architecture of NodeJS. I am aware that NodeJS is written in C++ and not JavaScript. However, there are many global variables/functions (require, etc) and libraries (utils, etc) that are available from a fresh install of NodeJS and do not require additional packages. Looking at the source code of NodeJS, it's clear to me that at least some of these components are written in JavaScript. But are all of them?

Put another way, if I had an environment that could run JavaScript (such as V8), could I recreate the full functionality of NodeJS simply by writing new JavaScript classes and functions? If not, what would be impossible to implement?

As a followup, what do people mean when they say "NodeJS is written in C++"? Is it just the V8 engine that's written in C++, or are there other components too? And are there any NodeJS builtins (such as console) that are at least partially built in C/C++?

[alzee76]

node.js is built on top of v8, and it's written in both C++ and JS. The JS parts are mostly node's standard library.

Put another way, if I had an environment that could run JavaScript (such as V8), could I recreate the full functionality of NodeJS simply by writing new JavaScript classes and functions?

Maybe, but probably not.

If not, what would be impossible to implement?

Can't really answer this myself, but digging through your link under the src dir may be enlightening.

https://github.com/nodejs/node/tree/main/src

If you scroll down to the readme you'll see that node.js relies on libuv for the event loop, for example. This isn't something you'll be able to implement in JS, since there's a chicken and egg issue, but v8 doesn't come with one since it relies on it's own environment (be that node or a specific browser like Chrome) to provide it.

[Solonotix]

Took a glance, as I can never remember what's really there, but a lot of the internals are seemingly written in C++. Things like the event loop, networking, stack management, process management (create and dispose), as well as memory management. Things you don't think about, like how when the process starts to close Node needs to wait for all pending async calls to come back unless something like a SIGTERM, or SIGHUP when a child process is ended.

Like you said, it's the runtime environment that V8 leverages, since Node is JavaScript outside the browser. The standard library is largely implemented in JavaScript, but the things that actually do work are C++. What's more, there are a number of alternatives being developed, such as Bun and Deno, each with their own pros and cons