fix cleanArg and rework JSValue(app.Value)

[mlctrez]

This PR addresses #876

• Adds func JSValue(v Value) any to js_nowasm.go and changes return type on matching function in js_wasm.go
• Fixes cleanArg() where slices and functions were getting passed down incorrectly to syscall/js
• Some basic unit tests in js_wasm.go to validate fixes

[qizhanchan]

Any updates?

[mlctrez]

@qizhanchan

Maxence mentioned here that this and other PRs might possibly be included in V10:
#875 (comment)

[maxence-charriere]

Why do we need to add this in non wasm file?

[mlctrez]

Similar to app.ValueOf:

go-app/pkg/app/js.go

Lines 168 to 170 in 4af7476

	func ValueOf(x any) Value {
	return valueOf(x)
	}

There is a js implementation:

go-app/pkg/app/js_wasm.go

Lines 146 to 149 in 4af7476

	func valueOf(x any) Value {
	switch t := x.(type) {
	case value:
	x = t.Value

and a nowasm implementation:

go-app/pkg/app/js_nowasm.go

Lines 156 to 158 in 4af7476

	func valueOf(x any) Value {
	return value{}
	}

The nowasm code path is only there to allow compiles to work for both js and nowasm builds.

[maxence-charriere]

The question is more what is the usecase of this? The purpose is to deal with syscall/js which is never usable out of js env. this is the very reason why go-app wrapping it.

[mlctrez]

Apologies for the lack of explanation on this 😄

app.JSValue returns the underlying syscall/js.Value when provided an app.Value ✔️

Since this function signature returns syscall/js.Value it can only be compiled for GOOS=js

For issue #876 there is a need to return a promise to a javascript call in a UI component:

promise := app.Window().Get("Promise").New(app.FuncOf(goFunc))

Returning the promise directly will fail since app.Value cannot be converted by syscall/js.ValueOf

// fails with panic: ValueOf: invalid value
return promise

Using app.JSValue works, but the component will only compile for GOOS=js

return app.JSValue(promise)

With #907 and the removal of app.jsval this may be challenging to solve this use case.

Let me know if you'd like to see a PR to address this.

[maxence-charriere]

Good catch 👍

[mlctrez]

HI @maxence-charriere , do you have any feedback on the comments on this PR?

[maxence-charriere]

As I mentioned before, this was designed to deal specifically with syscall/js. I remember being able to deal with promise with the current API. I would rather try help you figure out how to solve that usecase before touching this.

[maxence-charriere]

@mlctrez here is a working promise example:

func TestPromise(t *testing.T) {
	callback := FuncOf(func(this Value, args []Value) any {
		args[0].Invoke("hi")
		return nil
	})
	defer callback.Release()

	var wg sync.WaitGroup
	wg.Add(1)

	promise := Window().Get("Promise").New(callback)
	promise.Then(func(v Value) {
		fmt.Println(v.String())
		wg.Done()
	})

	wg.Wait()
}

go-app/pkg/app  v10 ✗                                                                                                                1d20h ⚑ ◒
▶ GOARCH=wasm GOOS=js go test -run TestPromise

hi
PASS
ok  	github.com/maxence-charriere/go-app/v9/pkg/app	0.394s

[mlctrez]

@maxence-charriere - The PR was to address a few things:

1. "Fixes cleanArg() where slices and functions were getting passed down incorrectly to syscall/js"
   Not all of the changes to address this made it into js args adjustment #907
   I commented on what was missing:
   

2. The other change was an attempt to address the issue raised by javascript callbacks #876
   Very specifically, returning an app.Value ( a promise object ) back to javascript results in panic: ValueOf: invalid value
   The following code demonstrates this:

func (r *Root) OnMount(context app.Context) {
	app.Window().Set("goAppPromise", app.FuncOf(func(this app.Value, args []app.Value) any {
		callback := app.FuncOf(func(this app.Value, args []app.Value) any {
			args[0].Invoke("hi")
			return nil
		})
		return app.Window().Get("Promise").New(callback)
	}))
}

func (r *Root) Render() app.UI {
	return app.Button().Text("goAppPromise").OnClick(func(ctx app.Context, e app.Event) {
		app.Window().Get("goAppPromise").Invoke()
	})
}

There might be a better way to convert app.Value to js.Value before it is returned, but I'm not seeing an obvious solution other than what was proposed. This change was just to fix #876, so if that's the only place that this has come up then maybe it does not need fixing.

[maxence-charriere]

Hey @mlctrez. Took me a bit to figure out but I think #920 should solve the problem.

Any chance you can try this and let me know if you find any issues?

Also made a unit test that reproduces your issue: https://github.com/maxence-charriere/go-app/pull/920/files#diff-e781a4648c64c93583360ae1713b104b0b4ac501867795b383b585794695b485R26-R48

[mlctrez]

@maxence-charriere - this looks like it solves the return value issue and incorporates the cleanArgs changes from this PR.

I've long since removed the code that I used from #876

Perhaps @g4bwy can test also?

[mlctrez]

resolved by #920