Passing console output to Shiny reactively as a status update - r

Question

I have created an application using R and Shiny and want to output everything that happens in the console to a special status window in the Shiny app.
Here is how the skeleton of the function called by Shiny application looks.
myfunction = function(x,y,path....){
if(...){...}
cat("Reading Database\n")
df = read.csv(...)
cat("Processing\n")
#MORE CODE
}
I want a status bar that shows the progress of the called function by viewing the cat(...) console outputs.
If yes, can it be done without making any changes to the original function (making changes only in server.R and/or ui.R)?

Answer 1

Unfortunately I don't know how to do this with the normal Shiny approach of using reactivity. I tried getting it to work with textOuput+printText but I was unable. I'd love to see other solutions, but here is my solution that uses shinyjs package to update the element instead of using reactivity. I hope this works for you, it's pretty simple.
library(shiny)
library(shinyjs)
calculate <- function() {
lapply(1:5, function(x) {
message(x)
Sys.sleep(0.5)
})
message("Done")
}
runApp(shinyApp(
ui = fluidPage(
shinyjs::useShinyjs(), br(),
actionButton("btn","Click me"), br(), br(),
"Progress:",
tags$pre(id = "progress")
),
server = function(input,output, session) {
observeEvent(input$btn, {
withCallingHandlers({
shinyjs::text("progress", "")
calculate()
},
message = function(m) {
shinyjs::text(id = "progress", text = m$message, add = TRUE)
})
})
}
))