test262 VS Jint

Indeed. These may be even more important...

https://github.com/tc39/test262

I successfully executed the assert-true.js and assert-false.js tests in the harness folder of the test262 repo. (This folder is full of tests which test the test harness itself.)

I have used a few js engines in the past (nashorn, rhino, otto) and all had problems with missing edge cases in the APIs or really weird quirks in the interop with the host environment.

https://github.com/tc39/test262 is the ecma test suite.

rhino for example has extensive gaps:

Jint https://github.com/sebastienros/jint

There are quite a lot of ways to run scripting languages in C#. I've no idea what JSR223 is but .NET has DLR for example. There are also multiple libraries: IronPython, NLua, Jint and Jurassic for Javascript. There's also older version of CS-Script working with .NET Framework.

You can. Embeding lua is a trivial task, and I'm reasonably sure there even are plug-and-play solutions for that, and for JS there's JINT.

I personally use Jint (a multi-platform Javascript interpreter) since Roslyn is not available on mobile. It basically has the same kind of functionality as Roslyn, but it's JS. JS is well-known and accessible to everybody, but Roslyn might be faster since there's no double indirection when interpreting the script. It also depends on what language your users are comfortable with or could learn easily.

Ah yeah, I looked into it more and decompiled the game to find that it appears they're using Jint to interpret the Javascript, and from testing with someone's REPL BBS server I can find that it's a pretty well isolated environment. Only ways around it I can think of are by exploiting some vulnerability in the sandbox to do external requests, modding the game itself to update the api, or running a parallel server to do some janky communication through the save state data.

We used https://github.com/sebastienros/jint for scripting, it's ES5 JS implementation.

Jint is a JS interpreter with an integrated engine built in C#, like V8, he is responsible for all the base code execution as well as EcmaScript implementations such as default constructors, syntax, Promises... I studied its features in depth to start and it was a bit hard (in the beginning).

MelonRuntime is based on Jint, a JavaScript interpreter created by Sébastien Ros, software developer in the ASP.NET team at Microsoft. Melon works from bindings and functionalities injected into this interpreter together with external typing (provided by another package that comes with the default project generated by the command npx melon new) and built-in tools.