Any guidance on how to use await / top level await

[kpko]

Hi,

in the long term I want to execute async c# functions in JavaScript. With the recent advantages with async/await and top level awaits I tried integrating these functions again. I understand there is no implicit task/promise conversion so I tried to use the engine.RegisterPromise() method to return a promise using a simple delay method.

As of my understanding this should create a promise that gets resolved in 5 seconds. The promise should be awaitable because of top-level awaits.

using Jint;

var engine = new Engine();
engine.SetValue("delay", (int seconds) =>
{
    var promise = engine.RegisterPromise();
    _ = Task.Delay(seconds * 1000)
        .ContinueWith(_ => promise.Resolve("success"), TaskContinuationOptions.OnlyOnRanToCompletion)
        .ContinueWith(_ => promise.Reject("failed"), TaskContinuationOptions.OnlyOnFaulted);

    return promise.Promise;
});
var val = engine.Evaluate("await delay(5)");
Console.WriteLine(val.UnwrapIfPromise());

This errors with 'Unexpected token' though. I tried wrapping everything in an async method:

var val = engine.Evaluate("(async () => await delay(5))()");
Console.WriteLine(val.UnwrapIfPromise());

But then I get the error 'System.InvalidOperationException: 'UnwrapIfPromise' called before Promise was settled'. This error seems to occur in the .Evaluate() line so I can't even work around that using a task completion source or something.

Is it possible to use await to await a task (converted to promise) in a script at this point? Or is what I'm trying simply not possible now (or ever)? Is there something I am missing?

Thank you in advance!

[Xicy]

I tried to implement Task to Promise conversion in that PR #1567. It is working but it's not actually async, it's block the thread until resolve.
You can follow up in the pr. I hope PR helps to you :)