V8 VS ChaiScript

It sounds like you want to know how JavaScript is implemented in the browser. The thing is, there is no universal implementation for JavaScript. JavaScript defines a specification that must be adhered to, and then each browser vendor can implement it in whatever way they see fit, as long as it does the specified things. For example (and I'm not saying this is the case) it's entirely possible for Chrome to implement Array.sort() using merge sort, while Firefox implements it as quick sort. You can try to find the source code for the implementation in a certain browser, but that will not be universal. I imagine you can find out how it works in Chrome somewhere in https://chromium.googlesource.com/v8/v8.git, though I'm not sure exactly where.

chrome v8 commits referring to spread operator one of them: https://github.com/v8/v8/commit/93b3397e52d3faf38059718de335027e57b9690d

Looks like these are the two commits, based on the issue number:

https://github.com/v8/v8/commit/0981e91a4f8692af337e2588562a...

https://github.com/v8/v8/commit/a2cae2180a7a6d64ccdede44d730...

Although there could be others.

https://github.com/v8/v8/blob/master/src/objects/dictionary.h https://wiki.cdot.senecacollege.ca/wiki/Inline_Assembly_Language https://en.cppreference.com/w/c/language/asm https://en.wikipedia.org/wiki/Inline_assembler https://stackoverflow.com/questions/2268562/what-are-intrinsics https://www.codeproject.com/Articles/15971/Using-Inline-Assembly-in-C-C https://stackoverflow.com/questions/48518225/what-are-intrinsic-types-in-javascript https://stackoverflow.com/questions/12168575/executing-generated-assembler-inline

It must be a fairly large echo chamber since it has room for Clang, GCC, V8, OpenJDK, Roslyn, etc. (The Zend parser for PHP seems to use some flavor of YACC, but given PHP, I don't know if that strengthens or weakens my point.)

What you're describing is not really possible with JS. Your best bet would be to look at the "V8 engine" source code. It is the interpreter used in Node.js and Chrome (and I think Edge would be using it too as Edge is built on Chromium). But there is nothing forcing Node.js to use V8, there are other JS interpreters. https://github.com/v8/v8

is it like https://chaiscript.com/?

3) Similiar to 2, but use more common scripting languages: chai, cs-script, sol2 (c++ framework to embed lua)

A few years back I actually went and made a ChaiScript based video game engine (https://16bpp.net/blog/post/masala-a-chaiscript-game-engine/). The end goal for it was to be able to make a Pacman like clone, but have all of the game logic implemented in ChaiScript. I actually found out as I added more realtime elements (implemented in ChaiScript) that it started to take much longer to process the game logic; the "game loop FPS" was under 60, which is not good. I actually proposition that ChaiScript move to a bytecode VM (https://github.com/ChaiScript/ChaiScript/issues/266), but I'm guessing that no movement was made on that front.

Maybe ChaiScript? It is not exactly what you are looking for, but very similar, in my opinion.