Help with promises (await)

[pjebs]

@dop251
I have this JS script

function doSomething() {
  return new Promise((resolve) => {
     resolve("https://example.com/");
  });
}

globalThis.testpromise = async () => JSON.stringify(await doSomething());
globalThis.testpromise2 = () => doSomething();

I am trying to get the final string value out of JS world and into Go world. (Note: In my actual real-world project, doSomething() won't resolve immediately)

This works (returns https://example.com/):

	v, err := vm.RunString(`testpromise2()`)
	v.Export().(*goja.Promise).Result().Export().(string) // Returns https://example.com/
}

However this does not (returns an unresolved promise, that never resolves):

	v, err := vm.RunString(`testpromise()`)
	v.Export().(*goja.Promise).Result().Export().(string)
}

NOTE: v, err := vm.RunString("await testpromise()") produces a JS error.

[pjebs]

I think https://pkg.go.dev/github.com/dop251/goja#Runtime.NewPromise or https://pkg.go.dev/github.com/dop251/goja#Runtime.SetAsyncContextTracker have something to do with it:

goja/func_test.go

Line 212 in 46d383d

func TestAsyncContextTracker(t *testing.T) {

Does anyone know how to make it work. I don't understand the example in NewPromise.

NewPromise seems to create a function IN THE GO WORLD and runs, but sets a promise in the JS world and then eventually gets resolved in JS world once it resolves in the Go world. It appears to be the opposite of what I want.

I want to get a JS promise which resolves, and then get that value out of the JS world and into Go world.

This may be relevant too: grafana/k6@8418147

[pjebs]

@matthewmueller Did you manage to solve this issue you mentioned in #601

I'm trying to figure out this eventloop stuff to run svelte.Preprocess

import {  preprocess} from 'svelte/compiler';
globalThis.preprocess = async (...args) => JSON.stringify(await preprocess(...args));

Unfortunately preprocess returns a Promise