r - How to retrieve the client's current time and time zone when using Shiny?

Question

I'm wondering if there is some clever way of getting the clients current time and time zone in order to use it in the server.R part of a Shiny application. If not, what could be the easiest way of doing this?

Answer 1

I found out a method that works and which is just a small modification of the stackoverflow answer to Reading javascript variable into shiny/R on app load. It does not retrieve the actuall time zone, but well the time zone offset.

In ui.R

HTML('<input type="text" id="client_time" name="client_time" style="display: none;"> '),
HTML('<input type="text" id="client_time_zone_offset" name="client_time_zone_offset" style="display: none;"> '),

tags$script('
  $(function() {
    var time_now = new Date()
    $("input#client_time").val(time_now.getTime())
    $("input#client_time_zone_offset").val(time_now.getTimezoneOffset())
  });    
')

This above created two divs and the javascript code retrieves the clients time and time zone offset and put them in the divs.

In server.R

client_time <- reactive(as.numeric(input$client_time) / 1000) # in s
time_zone_offset <- reactive(as.numeric(input$client_time_zone_offset) * 60 ) # in s 

This above creates two reactive variables that can be used in the server code. For ease of handling I also transform input$client_time from ms to s and input$client_time_zone_offset from min to s.