Demo on debug panel, may be useful for large projects, something like this should be made into a convenience function and a basic part of shiny

server.R

# server.R

library("shiny")

shinyServer(
  function(input, output, session) {
   
    # Debug Area 
    
    output$Console <- renderUI({
        btnTags <- function(){tags$style(type = 'text/css',"")}
        if (is.null(input$console) || !nzchar(input$console) || input$console == 0) {
            btnTags <- function(){tags$style(type = 'text/css'
              , '#console {color: rgb(221,17,68);}'
              )}
        }
        list(btnTags(),actionButton(inputId = "console", label = "console"))
    })
       
    observe(label = "console", {
      if (is.null(input$console) || !nzchar(input$console)) {return()}
      if (input$console != 0) {
        options(browserNLdisabled = TRUE)
        saved_console <- ".RDuetConsole"
        if (file.exists(saved_console)) {load(saved_console)}
        isolate(browser())
        save(file=saved_console,list=ls(environment()))
      }
    })
    
    
  }
)

ui.R

# ui.R

library("shiny")

pageWithMultiPanels <- function(headerPanel,sidePanel,mainPanel,footerPanel) {
  bootstrapPage(div(class = "container-fluid"
    , div(class = "row-fluid", headerPanel)
    , div(class = "row-fluid", sidePanel, mainPanel)
    , div(class = "row-fluid", footerPanel)
  ) )
}

footerPanel <- function(...) {
  div(class="footer", hr(), ...)
}

shinyUI(
  pageWithMultiPanels(
    headerPanel = headerPanel(h5("Debug Panel - Demo"))
    ,
    mainPanel = mainPanel(
      helpText(h5("This is the app's main panel"))
      ,
      helpText(a("Demo based on shiny-discuss message by Alex Brown", href="https://groups.google.com/forum/#!topic/shiny-discuss/YIusppqZ8cg", target="_blank"))
    )
    ,
    sidePanel = sidebarPanel(
      helpText(h5("This is the app's side panel"))
      ,
      helpText(a("Demo by Patrick Toche, 14 January 2014", href="https://gist.github.com/ptoche/8405209", target="_blank"))
    )
    ,
    footerPanel = footerPanel(
      checkboxInput(inputId = "showDebug", label = "Debug?", value = FALSE)
      ,
      conditionalPanel(condition = "input.showDebug == true"
        , wellPanel(
          h5("Debug Panel:")
          , helpText(HTML("Click to run code in the console"))
          , uiOutput("Console"), br()
          , helpText(HTML("The console should display a Browse prompt: <code>Browse[1]></code>"))
          , helpText(HTML("Enter <code>c</code> at the prompt to stop communication with the console and resume with the shiny app"))
        )
      )
    )
  )
)