@javiercn Please discuss with @pavelsavara and @maraf what should be done with this feature. We can:

1. Go ahead with a reflection-based solution (this PR) that introduces one public API method but has bunch of obvious and possibly some non-obvious issues.
2. Use a simple static solution (Add statically-typed support for wrapping JS interop calls as C# delegates  #61721) which, however, introduces multiple overloads to cover different number of args and void/non-void calls.
3. Scratch the feature altogether.

Personally, I am for 2 or 3 for the reasons we already went through. However, I want to go ahead with the consensus in the wider team.

1. This PR adds reflection and the behavior is leaking into public API. It would be impossible to fix later for trimmability/NAOT.
2. is much better. I still dislike making OOP over RPC call easy, but that ship sailed for Blazor JS interop.
3. yes please, who asked for this "feature" anyway.

This PR adds reflection and the behavior is leaking into public API. It would be impossible to fix later for trimmability/NAOT.

Can you clarify what you mean about this impacting the public API? I'm not sue what you mean about the comment on trimmability/NAOT. What's the specific issue with the pattern (note we do the same thing all over the place).

If the solution to address this were to use a source generator instead, AsAsyncFunction could be replaced with a SG based solution relying on Interceptors, so this shouldn't be a problem.

is much better. I still dislike making OOP over RPC call easy, but that ship sailed for Blazor JS interop.

That's fine, sometimes we can change the approach our customers take, but others we can't.

yes please, who asked for this "feature" anyway.

As for demand, this is covered as part of #31151.

There are common patterns that make this very useful, like being able to import a JSModule and taking a reference to one of its exported functions for use later on, and being able to pass that around as a BCL type as opposed to taking a dependency on JS interop types.