A simple Shiny spy to tell Shiny that the session has closed

server.R

library(shiny)
data(pressure)
data(cars)

shinyServer(function(input, output, session) {
  
  # Partial example
  observe({
    
    print(input$shinyspy)
    })
  
  
})

shinyspy.js

var shinyspy = new Shiny.InputBinding();
$.extend(shinyspy, {
  find: function(scope) {
    return $(scope).find(".shinyspy");
  },
  getValue: function(el) {    
   return($(el).data("session"))

  },
  setValue: function(el, value) {
  },
  subscribe: function(el, callback) {
    $(el).on("closingshinysession.shinyspy", function(e) {            
      console.log("dfsdfs")
      callback();
    });
  },
  unsubscribe: function(el) {
    $(el).off(".shinyspy");
  }
});
Shiny.inputBindings.register(shinyspy);

ui.R

library(shiny)

shinyspy <- function() {
  tagList(
  HTML("<shinyspy class='shinyspy' id='shinyspy' data-session='open' / >")
  ,tags$script("$(window).on('beforeunload',function() {
              $('.shinyspy').data({session:'closed'}) 
               $('.shinyspy').trigger('closingshinysession')
            return('Shiny will get alert of this if you leave has been alerted?')
               })"))
}

shinyUI(
  basicPage(
    
    # Partial example
#     selectInput("dataset", "Dataset", c("diamonds", "rock", "pressure", "cars")),
#     conditionalPanel(
#       condition = "output.nrows",
#       checkboxInput("headonly", "Only use first 1000 rows"))    
#     ,
    shinyspy(),
    includeScript("shinyspy.js")
  )
  
)