How to realize real time log-info ouput step-by-step in observeEvent?

shiny
,
1

I'm trying to create a Shiny app that displays incremental step updates with 1-second delays between steps. While the code logic works in regular R scripts, it fails to show intermediate steps in Shiny - only the final result appears.

After clicking "Run!", the output should display "step1" "step2" "step3" step-by-step. But actually, they comes out all together.

here is my code:

library(shiny)

ui <- fluidPage(
  actionButton("run", "Run!"),
  textOutput("out")
)

server <- function(input, output, session) {
  data <- reactiveVal("step0")
  output$out <- renderText(
    data()
  )
  observeEvent(input$run, {
    for (i in 1:3) {
      Sys.sleep(1)
      data(paste0(isolate(data()), "\n step", i))
      
      output$out <- renderText(
        data()
      )
    }
  }) 
}

shinyApp(ui, server)

It looks like the UI freezes and only shows the final result

Thanks!!! :pray: :pray: :pray:

2

SO crosspost: r - Shiny - Inserting UI with a for loop returns the same elements in every outputs - Stack Overflow