title: How to update output in shiny app with user input
body: <p>I have only started using shiny 2 days back so forgive me if this is very naive question but I have looked around and cannot find a simple answer. I am creating an app that will take a while to complete. I want to keep the output updated with intermediate steps of the program. I can print to the output once the program completes but how do I print intermediate steps.</p>
  
  <p>Eg in the following minimal app code it prints the numbers 1 to 10 after 10 seconds but how can I make it print at each second interval?</p>
  
  <pre><code>library(shiny)
  
  runApp(list(
    ui = basicPage(
      h2('Multiple output'),
      actionButton("goButton", "Go!"),
      textOutput("out")
    ),
    server = function(input, output) {
      output$out = renderText({
        if(input$goButton == 1 ) {
          msg = NULL
          for(i in 1:10) {
            Sys.sleep(1)
            msg = paste(msg,i)
          }
          msg
        }
      })
    }
  ))
  </code></pre>