Get JsRuntime execution output

[gufoe]

Hello, I'd like to reopen the issue #11105 of getting something useful from the script evaluation of deno_code.

So, I'd like to use deno to interpret js at runtime and get the result, for instance:

let res = runtime.execute_script("<main>", "123");
assert!(res.unwrap() == serde_json::Value::from(123))

But I cannot understand how to transform a Global into something useful.

Is there any way to achieve this?
I know there has been discussion in #11129 about the return value not always being deserializable.
Couldn't a enum be returned?
Something like this:

enum EvalResult {
  Deserializable(?)
  Other(Global<Value>)
}

[lucacasonato]

There are two things you can do:

1. You can return a Global<Value> into a string using the v8 API:

    let value = isolate.execute_script("<anon>", "'hello' + ' world!'").unwrap();
    let mut scope = isolate.handle_scope();
    let value = value.get(&mut scope);
    let result = value.to_rust_string_lossy(&mut scope);
    println!("{}", result);

2. You can use serde_v8 to deserialize a V8 value into any Rust value that implements serde::Deserialize:

    let value = isolate.execute_script("<anon>", "'hello' + ' world!'").unwrap();
    let mut scope = isolate.handle_scope();
    let value = value.get(&mut scope);
    let result: String =  serde_v8::from_v8(value, &mut scope);
    println!("{}", result);

[gufoe]

Thank you!
Your scripts are right but don't compile, so here's the correct code:

First we execute the script:

let global_var = context.execute_script("<anon>", "1+1")
    .expect("Error in script");
let mut scope = context.handle_scope();

Then we can either:

1. Convert to rust string (NOTE: you will lose typings, so basically js values "2" and 2 will all be converted to the same string):

let value = global.open(&mut scope);
let value_str = value.to_rust_string_lossy(&mut scope);

2. You can cast to anything that implements serde::Deserialize:

let local_var = deno_core::v8::Local::new(&mut scope, global);
let serde_json = serde_v8::from_v8::<serde_json::Value>(&mut scope, local_var)
    .expect("Unable to deserialize");

[bartlomieju]

@gufoe thanks for checking out, could you maybe add your example to https://github.com/denoland/deno/tree/main/core/examples ?

[gufoe]

Done! I've created #12806