javascript to golang: confusing double casting is necessary for EventsOn callback

[benjamin-thomas]

Description

Hello,

I'm testing out your tool (which I find very enjoyable to use: congrats), and I've hit a little nail which is possibly a bug or at least would require a little more documentation here: https://wails.io/docs/howdoesitwork#calling-runtime-methods

I'm running on Wails CLI v2.0.0-beta.34 on Ubuntu 20.04.

I hope the screenshots below will be clear enough for you.

To Reproduce

Following the demo, I want to report a message from the frontend to the backend as soon as I click on the Greet button:

To do this, I trigger a custom event from the JS side:

However, after much fiddling, it seems that I have to double cast the slice of interfaces, which seems very odd

Expected behaviour

Could you please clarify if this is intended behavior?

I would expect line 68 to work.

In order to extract a second argument, I found that I also had to apply the same clunky double casting to it.

So unless I'm misunderstanding something, there seems to be a buggy behavior here: casting the first item of a slice of interfaces to a slice of interfaces in order to retrieve its singular value at index zero does not make sense.

I'm getting back into golang after a few years off so I hope I'm not doing something stupid and this won't be a dumb bug report ;)

Screenshots

No response

Attempted Fixes

• google search
• search more info in the docs
• tried to find a working example in the wild via sourcegraph (did not find any)
• searched these github issues

System Details

Wails CLI v2.0.0-beta.34


Scanning system - Please wait (this may take a long time)...Done.

System
------
OS:                     Ubuntu
Version:                20.04
ID:                     ubuntu
Go Version:             go1.18
Platform:               linux
Architecture:           amd64
Package Manager:        apt

Dependency      Package Name            Status          Version
----------      ------------            ------          -------
*docker         docker.io               Installed       20.10.7-0ubuntu5~20.04.2
gcc             build-essential         Installed       12.8ubuntu1.1
libgtk-3        libgtk-3-dev            Installed       3.24.20-0ubuntu1.1
libwebkit       libwebkit2gtk-4.0-dev   Installed       2.34.6-0ubuntu0.20.04.1
npm             npm                     Installed       8.5.0
*nsis           nsis                    Installed       v3.05-2
pkg-config      pkg-config              Installed       0.29.1-0ubuntu4

* - Optional Dependency

Diagnosis
---------
Your system is ready for Wails development!

Additional context

On a side note, I was confused by not being able to replace any mention of interface{} to any in the signature, or face a server crash and won't start.

I understood any is an alias to interface{} in go 1.18 so this is probably something you're already aware of and will fix later?

[leaanthony]

Hi Benjamin! Welcome back to Go.
You've spotted a couple of interesting things here... It looks like the arguments are being returned as a []interface{} but back through a variadic method. I will check this out when I have more time, but either way, changing it (even if it's wrong) is a breaking change so it needs thinking about a bit more. Wails has zero telemetry so I've no idea how many people this change would affect.
The second point about any is a valid catch. I'll change the reflection code to honour this.
As a side note: If you are keen on sending structured data back to Go, consider calling a method instead. There is support for structs in calls and the latest code on master makes this really easy on the frontend by having TS classes generated for you.

[leaanthony]

@benjamin-thomas - I've created a PR to address the double casting issue. If you could test, it would be great to get your feedback. Thanks. #1326

[leaanthony]

Regarding the any issue, Wails doesn't currently mandate go1.18 and apparently that causes a compilation issue, even if you use go1.18: https://stackoverflow.com/questions/71487498/why-do-i-get-undeclared-name-any-requires-version-go1-18-or-later-when-usin

[benjamin-thomas]

As a side note: If you are keen on sending structured data back to Go, consider calling a method instead.

Got ya thanks for the heads up @leaanthony :)

If you could test, it would be great to get your feedback

I'm confused about the dev workflow here. Could you advise me how to proceed?

I gathered I could fetch the latest code change via the git commit id:

go get github.com/wailsapp/wails/v2/cmd/wails@026e2309fda793ba877c7d682cb23046017b0256

This does change my go mod file, however running wails dev reverts it to v2.0.0-beta.34

I also tried to update the binary as so, but this seems to be not the correct way to go.

go install github.com/wailsapp/wails/v2/cmd/wails@026e2309fda793ba877c7d682cb23046017b0256

I also tried to fork the project but got into other issues.

Regarding the any issue, Wails doesn't currently mandate go1.18 and apparently that causes a compilation issue, even if you use go1.18:

Alright, it's no big deal ^^

[leaanthony]

Follow this guide: https://wails.io/docs/next/guides/bleeding-edge

[benjamin-thomas]

@leaanthony I tested pull/1326 it it looks good to me 👍

I would consider one last change: changing the type signature returned from runtime.d.ts.

From this

To this

(A type hint is necessary to squash a final warning in my IDE obviously)

---

I can then use the args in this manner, which feels natural:

Although, as you pointed, using a function from the backend would be more appropriate here.

[leaanthony]

Thanks for the feedback and glad it works. I'll update the definition file. Part of me feels we could do more and make it work like bound methods but then it only affects JS to Go and we have method binding for that...

[leaanthony]

Just merged the PR. The runtime.d.ts update will happen in another PR 👍 Please close this if you are happy with the outcome

[leaanthony]

@benjamin-thomas - closing this. Please reopen if you think there is more to do.