Client error console and inserted/removed UI elements about shiny HOT 1 CLOSED

library(shiny)

ui <- fluidPage(
  actionButton('insertBtn', 'Insert'),
  actionButton('removeBtn', 'Remove'),
  tabsetPanel(
    id = "tabs",
    tabPanel(
      "Base",
      "Base tab content. Other tabs will have their tab-specific text."
    )
  )
)

server <- function(input, output) {

  ## keep track of elements inserted and not yet removed
  inserted <- c()

  observeEvent(input$insertBtn, {
    count <- input$insertBtn
    # give the inserted element a unique id so we can remove it later
    new_tab_title <- paste('Tab', count)

    # push a new element in to the app
    insertTab(
      inputId = "tabs",
      tabPanel(
        title = new_tab_title,
        paste("Content for", new_tab_title)
      )
    )
    inserted <<- c(inserted, new_tab_title)
  })

  observeEvent(input$removeBtn, {
    # pop last inserted tab out of the app
    removeTab(
      inputId = "tabs",
      target = inserted[length(inserted)]
    )
    # and remove it from the list of inserted elements
    inserted <<- inserted[-length(inserted)]
  })

}

shinyApp(ui, server)