session$sendBinaryMessage and Shiny.addBinaryMessageHandler are not working properly

[Wang-Hsiang-Sheng]

I have a large dataset which is stored in binary format and I want to send chunks of data dynamically to client side JavaScript. However, when I use session$sendBinaryMessage function from server side and Shiny.addBinaryMessageHandler from client JavaScript, it shows up an error "Uncaught TypeError: Shiny.addBinaryMessageHandler is not a function".

A small example is provided as below. How can I fix the problem?

library(shiny)

runApp(
  list(ui = fluidPage(
    titlePanel("sendBinaryMessage example"),
    fluidRow(
      column(4, wellPanel(
        sliderInput("controller", "Controller:",
                    min = 1, max = 20, value = 15),
        singleton(
          tags$head(tags$script('Shiny.addBinaryMessageHandler("testmessage",
                                    function(message) {
                                      alert("function is running properly");
                                    }
                                  );'))
        )
      ))
    )
  )
  , server = function(input, output, session){
    observe({
      session$sendBinaryMessage(type = 'testmessage',
                                message = as.raw(1))
    })
  })
)