Bookmarking

Lecture 30

Dr. Eric Friedlander

College of Idaho
CSCI 2025 - Winter 2026

Deploying

Several ways to deploy an app

• Option 1: Posit Connect Cloud
• Option 2: shinyapps.io (has a free tier)
• Option 3: shinylive
• Option 4+: Ad-hoc deployment (e.g. AWS, a server you have, some other hosting service)
  • General rule of thumb: Cheaper = More Effort

The Basics

The Problem

• State: Shiny apps are dynamic. Users change inputs to explore data.
• Issue: If you copy the URL, it points to the initial state, not the current state.
• Solution: Bookmarking encodes the current state (inputs) into the URL.

Enabling Bookmarking

1. UI: Add a bookmarkButton().
2. ShinyApp: Set enableBookmarking = "url".

ui <- function(request) {
  fluidPage(
    textInput("txt", "Text"),
    bookmarkButton()
  )
}

server <- function(input, output, session) { }

shinyApp(ui, server, enableBookmarking = "url")

Note: ui must be a function that takes request as an argument.

Advanced Bookmarking

Automatic URL Update

• Goal: Update the URL bar automatically as inputs change (no button needed).
• Server Logic:
  1. Observe changes to input.
  2. Call session$doBookmark().
  3. Use onBookmarked to update the query string.

server <- function(input, output, session) {
  # Trigger bookmarking on input change
  observe({
    reactiveValuesToList(input)
    session$doBookmark()
  })
  
  # Update URL in browser
  onBookmarked(updateQueryString)
}

Storing State on Server

• enableBookmarking = "server":
  • Saves state to a file on the server.
  • URL becomes short (e.g., ?_state_id=123).
  • Useful when state is too large for a URL.

Storing Custom State

• Sometimes input isn’t enough (e.g., you have reactiveValues to save).
• onBookmark(function(state) { ... }): Save extra data to state$values.
• onRestore(function(state) { ... }): Read data from state$values and restore reactiveValues.

Wrap-Up

Takeaways

• Bookmarking makes apps shareable.
• Function UI: ui <- function(request) { ... } is required.
• Modes:
  • "url": State in URL (portable, limited size).
  • "server": State on server (short URL, requires storage).
• Automation: Use onBookmarked(updateQueryString) for seamless experience.

Do Next

1. Read Chapter 11: Bookmarking from Mastering Shiny.
2. There’s NO recitation Gem for this textbook but I recommend creating your own and adding the textbook chapter and these slides.
3. I reommend working through the Exercises in the textbook.
4. That’s it for tonight!