Capture console output for Shiny apps

[brianwdavis]

I used {progress} in a package, because I expect it to mostly be used in interactive sessions. However, I want to make a demo with Shiny for an upcoming conference, and I don't see a good way to capture the printed bars and show them in the app.

I tried using solutions like https://stackoverflow.com/questions/30474538/possible-to-show-console-messages-written-with-message-in-a-shiny-ui, but only got [1] "\r" printed in my HTML element.

I could rewrite my package to check for the context, and if it's Shiny instead of interactive(), switch to using the Shiny-native progress bars, but that's... not the best solution. Are there any straightforward ideas I'm missing here?

[hadley]

Once the condition branch has been merged you'll be able to use something like in hadley/mastering-shiny#113 — I'll update https://mastering-shiny.org/action-feedback.html#progress-bars when it's ready to try out.

[jeffreyxparker]

It's not great. But it works.

library(shiny)
library(progress)

foo <- function() {
    pb <- progress_bar$new(
        format = " [:bar] :current/:total (:percent) eta: :eta",
        total = 5, clear = FALSE)
    for(i in 1:5) {
        pb$tick()
        Sys.sleep(1)
    }
}

ui <- fluidPage(
    shinyjs::useShinyjs(),
    actionButton("start_pb","Start Progress Bar"),
    textOutput("pb")
)

server <- function(input, output) {

    observeEvent(input$start_pb, {
        withCallingHandlers({
            shinyjs::html("pb", "")
            foo()
        },
        message = function(m) {
            shinyjs::html(id = "pb", html = m$message, add = FALSE)
        })
    })

}

shinyApp(ui = ui, server = server)