Confirmation modal before closing an app

[arangaca]

The title says it all, how could I display display a confirmation modal before closing a Shiny app?

This is obviously possible to do it in JavaScript (e.g. javascript - Confirmation before closing of tab/browser - Stack Overflow) but I was wondering if there's a built-in Shiny solution to do that in R.

[ismirsehregal]

You can use your preferred JS solution in shiny like this:

library(shiny)

ui <- fluidPage(
  tags$script(HTML("
  Shiny.initializedPromise.then(() => {
    alert('test');
    // your JS code
  });"))
)

server <- function(input, output, session) {}

shinyApp(ui, server)

However, it seems to me that most custom JS solutions do not work reliably for different reasons:

Warn user before leaving web page with unsaved changes

[arangaca]

Thanks but I couldn't find an event that works well when closing the app. Sadly the onbeforeunload/beforeunload events don't seem to be robust solutions on the system I'm working on.