在 R shiny 中，如何检查元素是否隐藏？

Question

if (interactive()) {

ui <- fluidPage(
  shinyjs::hidden(sliderInput("obs", "Number of observations", 0, 1000, 500)),
  actionButton("goButton", "Go!"),
  plotOutput("distPlot")
)

server <- function(input, output) {
  output$distPlot <- renderPlot({
    # Take a dependency on input$goButton. This will run once initially,
    # because the value changes from NULL to 0.
    input$goButton

    # Use isolate() to avoid dependency on input$obs
    dist <- isolate(rnorm(input$obs))
    hist(dist)
  })
}

shinyApp(ui, server)

}

obs是隐藏的。 如何在服务器 function 中检查它？