Defining Javascript classes programmatically in Jint 3

[hcaandersen]

In Jint 3, how do I either (a) define Javascript classes programmatically or (b) allow scripts to have the keyword, new, before function calls?

Scripts like var c = new MyClass() worked with the (very) old version that I was using, but fail in Jint 3 with the exception "MyClass is not a constructor".

Note that MyClass is currently defined programmatically (in C#) as a function. I've tried to work out how to define classes programmatically, but haven't yet succeeded. I'd prefer not to do so, as my code, which defines them as functions, work fine as long as I don't use the new keyword.

[lahma]

Did you check the examples in readme?

[lahma]

You drive a hard bargain for that IConstructor going back to public, and there's an ask already: #1144 . I don't find the programming model nice, but if that's what is wanted, maybe it needs to be available then. I'll probably create a PR to publish it and cover with public API tests.

We didn't want to expose CLR objects in Javascript because then (1) they'd have methods like ToString(), Equals() and GetHashCode(), and (2) scripts written by users would have access to other .NET classes, which would post a security risk. We therefore added each 'class' by adding an instance of JsFunction to GlobalScope using the following C# code:

Interop has gone a long way here, you can create member filters that allow you to have rules what to expose and some have created filters that use their own attributes. like [ExposeToJs] public void GetOrder(int id) { ... }. That's the way I would probably do it, here are some test cases to show usage: https://github.com/sebastienros/jint/blob/main/Jint.Tests/Runtime/InteropTests.MemberAccess.cs . Filters and direct interop expose would probably lead to less code, especially now that Jint has a lot of smarts with method overload discovery and parameter conversion.

[cyraid]

@lahma Any chance JInt could include a MemberAccessJSExposeAttribute that would do the MemberAccess for us? And we could just wire it up? Would save everyone a lot of code from programming it themselves. I see several questions of people asking for this, so it would be beneficial if something similar was included. :)

[cyraid]

@lahma sorry for all the questions, but does JInt cache the requests or should I do it myself?

[lahma]

Jint offers the flexibility that you can build upon. Someone might use interfaces etc so such attribute would not serve there. Easier for consumers to build the stuff they need.

I think Jint caches to some extent, you can test around with Jint code base with debugger attached.

[cyraid]

@lahma I get that, but it seems a common asked for feature would be what other embedded scripting engines have and that's attributes for methods/fields/etc.

Having those premade classes available so you could easily wire up your own by just using the convenience classes/methods from jint for the common use cases would go a long way.

I get that there may be little bandwidth, but maybe there could be a GitHub issue with a help wanted on it that someone could add? I'm sure it'd be trivial to add some common ones. Then maybe a doc how to wire it up? :)

[sebastienros]

@lahma will never get enough gifts https://github.com/sponsors/lahma

[hcaandersen]

Sorry, but I've gotten myself confused. Who is the main developer of Jint? Or are there multiple developers who've contributed equally?

[sebastienros]

I started the project but getting busy with other projects and work so for some time now @lahma is the boss and deserves all the credits for the recent improvements like ES6 features and performance work. Also why I sponsor him myself ;)

[hcaandersen]

I've given you both gifts. Thanks again!

[lahma]

Thank you very much! ❤️