ui <- function(req) {
  fluidPage(
    textInput("txt", "Text"),
    checkboxInput("chk", "Checkbox")
  )
}
server <- function(input, output, session) {
  observe({
    # Trigger this observer every time an input changes
    reactiveValuesToList(input)
    session$doBookmark()
  })
  onBookmarked(function(url) {
    updateQueryString(url)
  })
}

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