Call JavaScript from R directly

[shahreyar-abeer]

The documentation says we can call JavaScript like this.

app/js/index.js

export function sayHello() { console.log('Hello!'); }

code.R

tags$button(onclick = "App.sayHello()")

This works nicely.
But I want to call it directly from an observeEvent like this

observeEvent(input$button, {
    # run the JavaScript function sayHello
})

How do I do that?
I'm looking for something in the line of session$sendCustomMessage and not shinyjs

[kamilzyla]

Hi @shahreyar-abeer, thanks for your question! I'd suggest a solution along these lines:

app/js/index.js

export function sayHello(name) {
  console.log(`Hello ${name}!`);
}

Shiny.addCustomMessageHandler('sayHello', sayHello);

app/main.R

box::use(
  shiny,
)

say_hello <- function(name, session = shiny$getDefaultReactiveDomain()) {
  session$sendCustomMessage("sayHello", name)
}

#' @export
ui <- function(id) {
  ns <- shiny$NS(id)
  shiny$bootstrapPage(
    shiny$textInput(ns("name"), "Your Name"),
    shiny$actionButton(ns("hello"), "Say Hello!")
  )
}

#' @export
server <- function(id) {
  shiny$moduleServer(id, function(input, output, session) {
    shiny$observeEvent(input$hello, say_hello(input$name))
  })
}

Notes

The call to Shiny.addCustomMessageHandler() in JS and the sayHello wrapper in R are a kind of boilerplate code which will be very similar for any such handler you define. We are considering to add a mechanism to Rhino so that such definitions would be included automatically 🙂

[shahreyar-abeer]

Hi @kamilzyla

Thanks for the answer!
So it's pretty much the same as before.
Just that we define the JS function separately with export instead of defining it inside Shiny.addCustomMessageHandler

Thanks a lot for the great package!

[kamilzyla]

I may add that the export keyword can be actually omitted in this case. It's only needed if you want to refer to the function via App.sayHello e.g. in an onclick handler 😉

[shahreyar-abeer]

Uh I see.
Thanks for the clarification!