Shiny Modules (part 3): Dynamic module call

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On the previous post “Share reactive among multiple modules” we showed how to send/get data to/from modules.

Now that toying with modules has no more secret for you. You may want to call one module multiple times without having to explicitly code it ?

On this article we will see how to call a module dynamically and how to manage its outputs from both server and ui side with 2 examples:

  • Dynamic call to get UI output
  • Dynamic call to get both UI & server outputs.

Want to run the examples ?

All code used in this post are available in Github ardata-fr/Shiny-Modules-Tutorials. This repository is actually an R package containing all the modules. Applications are stored in the folder inst.

To get apps locally, install the package and run applications:

# install.packages("remotes")
# List available applications
# Run first application

Example 1: Get the UI output

As seen in the previous article, your module is split into 2 funtions. The UI side and the Server logic.

In this example, the server logic has no return. So we just need to handle the UI output.

Online application or use command:

# Run Shiny application

NB: On this example each UI output is a shinyWidgets::panel.

Application demo

Application demo

Initialize rv$all_ui

On the application the reactiveValues rv is initialized as below:

rv <- reactiveValues(all_ui = list())

Dynamic call through observeEvent

Every time a dataset is loaded (eg: data_mod1$trigger increments) the observeEvent:

  1. launch the module server logic
    module = data_info,
    id = data_mod1$trigger,
    data = data_mod1$data,
    data_name = data_mod1$data_name
  1. Get the module UI output in the reactive rv$all_ui
rv$all_ui[[data_mod1$trigger]] <- data_infoUI(id = data_mod1$trigger)

Render UI elements

Note that the UI element returned by the module is a shinyWidgets::panel. Thus, we can use it in a simple tagList function.

output$all_results <- renderUI({

Example 2: Get the UI & server outputs

Remember the example whole-app on the previous article ?

You can still get it online here or use command:

# Run Shiny application

For the next example, I created a module merge_modules that contains all the modules used in whole-app except the load_data.
The idea here is to set only once the module load_data and then call the module merge_modules every time the user load a data:

Ce “super-module” merge_modules retourne les parties UI de tous les modules sous-jacents. Sa partie server renvoi une reactiveValues contenant le nom ainsi que le nombre de fonction appliqués sur chaque jeux de données chargés.

This module return every nested modules UI and a reactiveValues containing the name of dataset loaded & the number of functions applied.

Online application or use command:

# Run Shiny application

NB: On this example we will use a tabsetPanel, each UI output will be stored inside a new tabPanel. Moreover, each tabPanel contains a close button inside its title.

Application demo

Application demo

Variables initialization

trick     <- reactiveVal(0)
res       <- list()
obs_close <- list()
  • The reactiveVal trick is an integer that incremente every time the user call the module merge_modules. It is used as an id for the tabPanel and for list res names.
  • The list res contains each server logic return of modules merge_modules.
  • The list obs_close contains observers that trigger to close a tabPanel.

Dynamic call through observeEvent

Every time a dataset is loaded (eg: data_mod1$trigger increments) the observeEvent:

  1. launch the module server logic and store result inside res
res[[paste(id)]] <<- callModule(
    module = merge_modules,
    id = id,
    data = data,
    name = name
  1. Get the module UI output in a new tabPanel:
    inputId = "all_tabs",
        title = tabTitle(name, id),
        value = id,
        merge_modulesUI(id = id)
    select = TRUE
  1. Add to obs_close an observer to trigger tabPanel close:
obs_close[[paste(id)]] <<- observe({
    shinyjs::onclick(id = paste0("close", id), closeTab(id = id))
  1. Incremente the reactiveValue trick
trick(trick() + 1)

Incrementing trick will trigger the renderUI: ui_summary

The reactiveVal trick is used to trigger an update in the renderUI ui_summary because the list res isn’t reactive itself !

Use server outputs in application

You can use the list res elsewhere in your application. However don’t forget to reference the trick reactiveVal to be sure your reactive context updates.

# Summary of all opened tabs
output$ui_summary <- renderUI({
    # Reference trick to update reactive context
    fool <- trick()
    zz <- lapply(res, reactiveValuesToList)

    if (length(zz) == 0) {
        content <- div(class = "warn ", "No variable loaded")
    } else {
        # Use output of module merge_modules:
        #  - name
        #  - nb_funs
        content <- tags$ul(
          lapply(zz, function(x) {
            tags$li(paste(x$name, ":", x$nb_funs))


Bonus: Close a tabPanel

In our example we can “revert” a dynamic module call. To do so, we need to undo what’s done in the previous chapter:

  • Remove a tabPanel (UI part).
  • Remove related element from list res (Server part).

This 2 steps are part of the function closeTab described below. This function is called in the observe created dynamically (eg previous chapter):

closeTab <- function(id) {
    # Remove tab from UI
    removeTab(inputId = "all_tabs", target = paste(id))
    # Remove related element from list
    res[[paste(id)]] <<- NULL
    # Increase trick to refresh output$ui_summary
    trick(trick() + 1)

Note that the cross “button” inside the tabPanel title is created with function below:

# Function to add a cross after tabPanel title
tabTitle <- function(name, id) {
        name, HTML(" "),
            id = paste0("close", id),
            class = "close",


Call dynamically your module is usefull when :

  • the module can be called an indefinite number of times.
  • the module is called through a user action.

The call must be done inside an observeEvent or observe and then:

  • If you need server output, store results inside a new element of a list.

  • For UI there are 2 solutions:

    • Store UI output inside a reactiveValues (example 1).
    • Use UI output directly (example 2).

Be a shiny module master

Along trough our 3 articles we saw:

I hope these articles will help you to have fun developping awesome Shiny applications !

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