title: r shiny - uiOutput not rendering inside menuItem
body: <p><strong>Question</strong></p>
  
  <p>Why does a <code>sliderInput()</code> that's generated on the <code>server</code>, and rendered on the <code>ui</code> with <code>uiOutput()</code> not get displayed in a <code>menuItem()</code>?</p>
  
  <p><strong>Example</strong></p>
  
  <p>In this simple app I'm generating a <code>sliderInput</code> on the <code>server</code> (note the <code>menuItem</code> is deliberately commented out), and it works as expected</p>
  
  <pre><code>library(shiny)
  library(shinydashboard)
  
  rm(ui, server)
  
  ui &lt;- dashboardPage(
      dashboardHeader(),
  
      dashboardSidebar(
          sidebarMenu(
              #menuItem(text = "data options",
                        checkboxGroupInput(inputId = "cbg_group1", label = "group 1", 
                                           choices = c("some","check","boxes","to","choose","from") ),
                         uiOutput("sli_val1"),
                         checkboxGroupInput(inputId = "cbg_group2", label = "group 2", 
                                            choices = c("another","set","of","check","boxes") ),
              #                ),
              menuItem(text = "another tab")
              )
      ),
      dashboardBody()
  )
  
  server &lt;- function(input, output, session){
  
      withProgress(message = "loading page", value=0.1, {
          ## simulate loading some data
          Sys.sleep(3)
  
          ## slider input
          output$sli_val1 &lt;- renderUI({
              sliderInput(inputId = "sli_val1", 
                          label = "values", min = 0, max = 100,
                          value = c(25, 75) )
          })
          setProgress(value=1, detail="Complete")
      })
  }
  
  shinyApp(ui = ui, server = server)
  </code></pre>
  
  <p>However, when I move the <code>uiOutput</code> inside a <code>menuItem( )</code>, the output no longer renders:</p>
  
  <pre><code>ui &lt;- dashboardPage(
      dashboardHeader(),
  
      dashboardSidebar(
          sidebarMenu(
              menuItem(text = "data options",
                       checkboxGroupInput(inputId = "cbg_group1", label = "group 1", 
                                          choices = c("some","check","boxes","to","choose","from") ),
                       uiOutput("sli_val1"),
                       checkboxGroupInput(inputId = "cbg_group2", label = "group 2", 
                                          choices = c("another","set","of","check","boxes") )
                               ),
              menuItem(text = "another tab")
              )
      ),
      dashboardBody()
  )
  </code></pre>