Demo demonstrating how to dynamically add and remove Shiny modules, and how to properly clean up modules once removed by using the destroy() method.

shiny-destroy-observer.R

# Dynamic UI: demonstrate destroy() method on observer
# This example makes use of a module that dynamically creates pages
# Each server part of the module creates an observer that listens to an actionButton
# Whenever a page is removed, the observer is destroyed. The UI is removed with
# the nav_remove() function.

library(shiny)
library(bslib)

sportsPageUI <- function(id, page_name) {
  ns <- NS(id)
  tagList(
    h2(page_name),
    card(
      card_header("General Info"),
      card_body(
        textOutput(ns("general_info")),
        actionButton(ns("notification"), "Show notification")
      )
    )
  )
} 

sportsPageServer <- function(id, chosen_sport, r) {
  moduleServer(id, function(input, output, session) {
    
    output$general_info <- renderText({
      sprintf("%s is the sports you have chosen!", chosen_sport)
    })
    
    my_observer <-
      observe({
        showNotification(sprintf("Welcome to the %s page!", chosen_sport))
      }) |> bindEvent(input$notification)
    
    r$observer_list[[id]] <- my_observer
    
  })
}

ui <- page_navbar(
  id = "navbar_id",
  title = "Destroy modules",
  nav_menu(title = "Sports",
           icon = icon("basketball-ball"),
           nav_panel(title = "Add sports",
                     icon = icon("cogs"),
                     selectInput("sports_to_add",
                                 label = "Choose sports to add",
                                 choices = c("Baseball", 
                                             "Basketball", 
                                             "Football", 
                                             "Tennis"),
                                 selected = NULL,
                                 multiple = TRUE)
           )
  )
)

server <- function(input, output, session) {
  
  r <- reactiveValues(active_pages = NULL,
                      observer_list = list())
  
  observe({
    
    chosen_sports <- input$sports_to_add
    
    lapply(chosen_sports, function(this_sport) {
      
      if (this_sport %in% r$active_pages) { 
        # the sport already has a page, and is chosen by the user, so don't do anything
        return()
      }
      
      nav_insert(id = "navbar_id",
                 target = "Add sports",
                 nav = nav_panel(
                   title = this_sport,
                   icon = icon("plus-circle"),
                   sportsPageUI(id = this_sport, page_name = this_sport)
                 ),
                 position = "after")
      
      sportsPageServer(id = this_sport, chosen_sport = this_sport, r = r)
      
    })
    
    if (setdiff(r$active_pages, chosen_sports) |> length() > 0) {
      
      remove_sports <- setdiff(r$active_pages, chosen_sports)
      
      for (sport in remove_sports) {
        nav_remove(id = "navbar_id",
                   target = sport)
        
        # destroy any existing observers
        r$observer_list[[sport]]$destroy()
        
      }
      
    }
    
    r$active_pages <- chosen_sports
    
  }) |> bindEvent(input$sports_to_add)
  
}

shinyApp(ui, server)