Proper prototype handling

[Ablu]

Problem

Currently JavaScript.Net does not fully support prototype related use cases:

While it is possible to register a function which creates a new object like this:

_context.SetParameter("TestClass", new Func<TestClass>(() => new TestClass()));

_context.Run(@"
    let c = new TestClass();
    c.foo()").Should().Be(true);

problems with this approach:

• instanceOf checks are not working. c instanceof TestClass is false
• Prototype extensions are not working (TestClass.prototype.newMethod = function() {...})

Things to consider for the solution

• Objects which are created by C# code should also be able to pass to JavaScript under an existing prototype
• Fine grained control about which types are constructable by JS is required

Solution proposal

• add method like SetConstructor(ConstructorInfo constructor) to the context which generates a prototype and registers under the name
• when wrapping an object:
  • lookup whether a prototype already exists for the type
  • if no prototype is known: generate a prototype (but do not make it available to the context under a name)
  • wrap object by using the newly generated or existing prototype

Side notes

This could also improve performance of wrapping objects since the analysis of type is only required once, repetitive passing could become a lot faster.

---

/cc @spahnke

@oliverbock do you think the proposal above is sane? Then I would start to implement it.

[oliverbock]

Sounds hard to implement, but useful. What will ConstructorInfo contain? Can you distinguish between the C# class instance (maps to the JavaScript object) and the C# method definitions (maps to the JavaScript object's prototype)?

[Ablu]

With ConstructorInfo I meant https://docs.microsoft.com/en-us/dotnet/api/system.reflection.constructorinfo?view=netframework-4.7.2. So I get full access to the type via DeclaringType.

[Ablu]

I will break it into small self-contained tasks:

1. change the current wrapping logic to be prototype based
2. reuse prototypes for same types
3. add actual support for JS called constructors

This hopefully keeps the individual PRs reviewable and small(er)

[Ablu]

It was simpler than anticipated before. The linked PR (#71) should fix/add this. The only thing which might need more work is inheritance on .NET side... However, I guess that could be handled as a separate issue (not sure whether we need it at the moment)?

[Ablu]

Also we just realized that overloaded constructors would need additional support