Using observe function in shiny R

Question

I am trying to send the value of a JavaScript variable from ui.R to Server.R whenever it is changed. When a user clicks on a link, its href value is alerted . Till here it works fine. The links are of the form

<a href="something.com" onclick=\"clickFunction(this.href); return false;\" target=\"_blank\">Sample link </a>

Now, the href value is stored in variable link in ui.R . I am sending the value of link to server.R using Shiny.onInputChange function.

But the observe function in server.R is not giving me any value. Please tell me how to do this by using observe function or any other way if possible.

ui.r

library(shiny)
shinyUI(fluidPage(

  tags$script(HTML("
                      function clickFunction(link){
                          alert(link); 
                          Shiny.onInputChange(\"linkClicked\",link);   
                      }
                     "))

//rest of the code which is not related

)

server.R

library(shiny)

shinyServer(function(input, output) {

  observe({
    input$linkClicked
    print(input$linkClicked)
  })
})

Answer 1

I don't really fully understand where the link is coming from and how the app looks since you didn't provide enough code (for example: what does it mean "variable in the UI"?). But here's a small example that shows how the javascript sends info to the server successfully. I'm using the shinyjs package which is a package I wrote.

library(shinyjs)
jscode <- "
shinyjs.clickfunc = function(link) {
  alert(link);  
  Shiny.onInputChange('linkClicked', link);
}"

runApp(shinyApp(
  ui = fluidPage(
    useShinyjs(),
    extendShinyjs(text = jscode),
    textInput("link", ""),
    actionButton("btn", "submit")
  ),
  server = function(input, output, session) {
    observeEvent(input$btn, {
      js$clickfunc(input$link)
    })
    observe({
      input$linkClicked
      print(input$linkClicked)
    })
  }
))

EDIT :

If I understand correctly how the links are generated, this works

runApp(shinyApp(
  ui = fluidPage(
    tags$script(HTML("
                      function clickFunction(link){
                          alert(link); 
                          Shiny.onInputChange('linkClicked',link);   
                      }
                     ")),
    tags$a(href="www.google.com", onclick="clickFunction('rstudio.org'); return false;", "click me")
  ),
  server = function(input, output, session) {
    observe({
      input$linkClicked
      print(input$linkClicked)
    })
  }
))