V8 VS Duktape

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

Im my projects I search for single file libs.(like https://github.com/svaarala/duktape etc...)

You can also refer to the Unicode routines of other small JS engines[1,2], those don’t use ICU either, although the implementations are mercilessly size-optimized (to put it politely) and restricted to what the target JS version requires (e.g. casemapping but no normalization).

[1] https://github.com/bellard/quickjs/blob/master/libunicode.c

[2] https://github.com/svaarala/duktape/blob/master/src-input/du...

> memcpy from bytes to a NaN should work fine

Signaling NaNs are explicitly undefined in C11 F.2.1.: "This specification does not define the behavior of signaling NaNs." - and in practice may be "quieted" by conversion to Quiet NaNs, changing their bit patterns. Fast math optimization flags will also break the hell out of your code by assuming NaNs are impossible. I want to say there are more circumstances where optimizers and compiler generated code can butcher your NaN payloads, but I'd be working off recollected hearsay and I can't find a source, so don't quote me on that.

NaN boxing is common enough that, if you take the right precautions, a modern compiler should probably support it, maybe. NaN boxing is uncommon enough that, if your codebase needs to be sufficiently portable, you need an opt out for when it breaks. Let's review duktape's scars:

https://github.com/svaarala/duktape/blob/123d9426d5e5b36d5da...

https://github.com/svaarala/duktape/blob/5252b7a50611a3cb8bf...

https://github.com/svaarala/duktape/blob/224a0b89ca08a36e37e...

Note that "the right precautions" involve unions and proper integer types to avoid optimizer-invoked rewrites of the value and debugging when things go wrong, not simply YOLOing bytes into a double via memcpy. Note that debugging when it all goes terribly wrong can be quite painful. I've personally had the misfortune of being forced to debug duktape being built with fast math optimizatoins enabled on one "rare" platform + build configuration that wasn't caught by duktape's #if defined(__FAST_MATH__) checks linked above (wasn't Clang nor GCC, so go figure it didn't make the same #define)

I was expecting this to be about Duktape <https://github.com/svaarala/duktape>, but heh, for sure no. I'd bet $1 there's no way youtube-dl would switch, but I wonder if yt-dlp would?

- Duktape (4.8k stars)