deno_core: Asynchronous cannot obtain return value

let script_with_params = "(async () => {12})()";
    // execute_script_static
    let result = runtime.execute_script_static("<user-script>", &script_with_params)?;
    // run_event_loop
    runtime.run_event_loop(PollEventLoopOptions::default()).await?;

    let scope = &mut runtime.handle_scope();
    let local = v8::Local::new(scope, result);
    // Deserialize a `v8` object into a Rust type using `serde_v8`,
    // in this case deserialize to a JSON `Value`.
    let deserialized_value =
        serde_v8::from_v8::<serde_json::Value>(scope, local);
    Ok(deserialized_value.unwrap().to_string())

result:    {}

Excuse me, how should I write it to correctly obtain the return value within asynchrony？

About this issue

Original URL
State: closed
Created 6 months ago
Comments: 18 (10 by maintainers)

Most upvoted comments

Hello,

Thank you for your continued support. I wanted to update you on my progress and also seek your opinion on an approach I’ve tried.

I managed to execute the script and retrieve the value using the following method:

let promise_global = runtime.execute_script("<user-script>", FastString::Owned(Box::from(script_with_params)))?;
runtime.run_event_loop(PollEventLoopOptions::default()).await?;
let scope = &mut runtime.handle_scope();
let result_global = v8::Local::new(scope, promise_global);
let promise = unsafe { v8::Local::<v8::Promise>::cast(result_global) }; // use unsafe
let result = promise.result(scope).to_rust_string_lossy(scope);

This method seems to work for executing the script and retrieving the value. However, I am wondering if there is an even better or more efficient way to achieve this. Particularly, I’m interested in understanding if there’s a way to optimize the handling of promises and the extraction of their results.

Any further insights or suggestions you could provide would be greatly appreciated.

Thank you once again for your assistance.

huiali on Dec 23, 2023

That’s fine, but then I think docstring on JsRuntime::resolve should hint that the event loop needs to be polled, from what it reads right now:

/// Waits for the given value to resolve while polling the event loop.
  ///
  /// This future resolves when either the value is resolved or the event loop runs to
  /// completion.

it hints that it automatically runs the event loop.

bartlomieju on Dec 19, 2023