"resolved is undefined" error with screenshotButton in shinylive

[barryrowlingson]

I've been asked to get a shiny app running on shinylive (in-browser running of shiny apps via webr) and I get this error image:

unless I comment out the screenshotButton call in the ui section, in which case the app works fine in the browser.

I can only guess this is because of the way browser screenshot code works, and its beyond me to debug it at this time. My main motivation for reporting it here is so if anyone searches for "shinylive resolved is undefined" they can see this and it will save them a bunch of debugging to discover the issue is with screenshotButton.

[daattali]

Thanks for the report. I have no clue how to debug within shinylive, was there any error log anywhere? Either in javascript or elsewhere?

[barryrowlingson]

I've just discovered in a minimal shiny app that adding an actionButton to the ui and using screenshot in the server works in shinylive, whereas screenshotButton in the ui fails. If that's fully equivalent to the screenshotButton then I'll go with that, assuming I can get that working in the app I'm trying to make work. Hopeful!

There are lots of "error" messages on the browser console but they happen even when a shinylive app is working perfectly. The only extra errors are these two entries and the scary skeleton face in the browser:

preload error:resolved is undefined shinylive.js:34938:38
    _error http://127.0.0.1:7446/shinylive/shinylive.js:34938
    error http://127.0.0.1:7446/shinylive/shinylive.js:34944
    runRAsync http://127.0.0.1:7446/shinylive/shinylive.js:33571
resolved is undefined shinylive.js:34794:19
    runApp2 http://127.0.0.1:7446/shinylive/shinylive.js:34794

[daattali]

They have extremely similar paths, that end up in the same place, and they're meant to be as identical as possible. Any difference that you see between the two is not be design, so yes if you can make it work with one of them then you should use it. I really don't know how to even begin debugging this in shinylive

[gadenbuie]

It appears the core issue may have been fixed: the example in the shinyscreenshot README appears to work in shinylive. Or, at least it doesn't fail loudly. It does have trouble loading Shiny's CSS files so the screenshots aren't great. But the core functionality seems to be working.

https://shinylive.io/r/editor/#code=NobwRAdghgtgpmAXGKAHVA6ASmANGAYwHsIAXOMpMAGwEsAjAJykYE8AKAZwAtaJWAlAB0IdJiw48+rTgUZwKPIqWEQRAV1oACADwBaLQDNqmgCYAFKAHM47EVq3kAHqQCSEVOtJ2wz0kLwtAIBRMjhGLU4ieEc4FwDcIN84Tn8wAVx7LSgCUloSACEvUhIfKyIEpIAVKABrOGzIuQUIJTTVVRFOcIA3cN0DQ3UIXPyIdj5PUkSiLymBLRAsonpuxj7gvrIJjy8AEnLEpYgHB1l5RW5ldlUHAF9VO5Eu3n4AQXR2TUS1vsYBMB3AC6QA

[daattali]

It does seem that this issue is working now, works for me. @barryrowlingson can you confirm you can use screenshotButton() now?

[daattali]

@gadenbuie any idea why CSS files are not being loaded when using shinylive? Is this something that can be fixed?

Code:

library(shiny)
library(shinyscreenshot)

ui <- fluidPage(
  textInput("text", "Enter some text", "test"),
  actionButton("go", "Take a screenshot")
)

server <- function(input, output) {
  observeEvent(input$go, {
    screenshot()
  })
}

shinyApp(ui, server)

[gadenbuie]

I don't know exactly why, but I suspect it'll be tricky to fix. The Shiny app is running in a service worker and I think that html2canvas also uses a service worker, so without some additional work (vague and ambiguous because I don't know exactly what work) the html2canvas service worker isn't allowed to request resources from Shiny's service worker.

[daattali]

As far as I can tell, html2canvas does not use service workers. Anyway, I imagine this is not something Posit will dedicate too much more time investing, so I should just accept that shinylive is not supported for this package, right?

[gadenbuie]

As far as I can tell, html2canvas does not use service workers.

Ah, sorry, I thought I saw documentation saying it did but now I can't find it.