R Shiny Two Outputs for One Action Button - r

Question

I'm trying to use an action button in R Shiny to start a slow-running JAGS model. I would like some text to appear when the user first hits the button that displays what time they pressed the button so that they know something is happening.
So far, the action button is working but it waits until the slow-running model is done to display both the model output and the text.
I have looked at the following questions but they don't seem to answer my question, at least not in a way I understand:
R Shiny execute order
Pattern for triggering a series of Shiny actions
I am new to Shiny so I'm hoping this is a simple problem.
Run.me <- function(a){
# some fake slow function
# This actually takes about 8 hours in real life
for (i in 2:a) {
Foo[i] <<- Foo[i-1] + sample(1:20,1)
}}
library(shiny)
Define server logic ----
server <- function(input, output) {
observeEvent(input$runmodel, {
output$model.running <- renderText({paste("Model started at", Sys.time())})
})
observeEvent(input$runmodel, {
Foo <<- rep(1, 1e6)
Run.me(1e6)
output$model.ran <- renderTable({head(Foo)})
})
}
Define UI ----
ui <- fluidPage(
fluidRow(
column(5, align = "center",
actionButton("runmodel", "Run the Model")),
textOutput("model.running")
),
fluidRow(
column(5, align = "center", tableOutput("model.ran"))
)
)
Run the app ----
shinyApp(ui = ui, server = server)

Answer 1

A possibility, if I correctly understand the question:
server <- function(input, output) {
observeEvent(input$runmodel, {
Foo <<- rep(1, 1e6)
Run.me(1e6)
output$modelran <- renderTable({head(Foo)})
})
}
js <- "
$(document).ready(function() {
$('#runmodel').on('click', function(){
var date = new Date().toLocaleString();
$('#busy').html('Model started: ' + date);
});
$('#modelran').on('shiny:value', function(event) {
$('#busy').html('');
});
});
"
ui <- fluidPage(
tags$head(
tags$script(HTML(js))
),
fluidRow(
column(5, align = "center",
actionButton("runmodel", "Run the Model")),
tags$p(id = "busy")
),
fluidRow(
column(5, align = "center", tableOutput("modelran"))
)
)

Answer 2

In my app which is also building a model slowly I use a progress bar in the server. I know this is not exactly what you are asking for but you might find it an acceptable solution.
modeloutput= reactive(withProgress(message = 'Generating JAGs model', value = 0, {
incProgress(50); generate_jags(params)
}))
output$jags = renderPlot(modeloutput())
I will also follow answers to this question as I would also prefer a solution that has a message or loading bar in the actual plotting window where the output will appear.
I've also found another solution that works by blocking out the action button after it has been clicked and has a small loading bar and completion message. It is available here:
https://github.com/daattali/advanced-shiny/tree/master/busy-indicator