simpleTab with visible tab id

server.R

library(shiny)
shinyServer(function(input, output) {
   cat('shinyServer called\n',file=stderr())

   output$foo <- reactivePrint(function(){
     cat('output$foo called\n',file=stderr())
     input
   })

   runIfVisible <- function(visibleTab,val,expr){
      if (visibleTab==val)
         return(eval(expr,parent.frame()))
      else
         return(NULL)
   }

   output$afunc <- reactivePrint(function() {
      runIfVisible(input$visibleTab,'A',{
         cat('output$afunc updated\n',file=stderr())
         input$n
      })
   })
   output$bfunc <- reactivePrint(function() {
      runIfVisible(input$visibleTab,'B',{
         cat('output$bfunc updated\n',file=stderr())
         Sys.sleep(4)
         input$n
      })
   })

   output$plot <- reactivePlot(function(){
      runIfVisible(input$visibleTab,'Plot',{
         cat('output$plot updated\n',file=stderr())
         plot(rnorm(input$n))
      })
   })

})

ui.R

library(shiny)
shinyUI(pageWithSidebar(
  # Application title
  headerPanel("Tabsets"),
  sidebarPanel(
    sliderInput("n",
                "Number of observations:",
                 value = 500,
                 min = 1,
                 max = 1000)
  ),
  mainPanel(
    tabsetPanel(
      tabPanel("A", verbatimTextOutput("afunc")),
      tabPanel("B", verbatimTextOutput("bfunc")),
      tabPanel("Plot",plotOutput('plot')),
      id='visibleTab'
    )
  )
))