r - Shiny Responds to Enter

Question

I have a textInput widget, and now whenever I start typing in the widget, shinyApp tries to evaluate the unfinished content in the textInput widget and results in many errors. I'm aware that adding an action Button "Calculate" would easily solve the problem. However, my app does not have space left for one more button. So, I'd like to know if there's a way that the textInput widget would "listen" to a keyboard event, such as when the user hits "Enter?" Thanks in advance!

Answer 1

Very good question. Here is an example of the way I use; this app shows a ggplot and the user gives the title of the ggplot in a textbox - but the title changes reacts only when "Return" is pressed:

js <- '
$(document).on("keyup", function(e) {
  if(e.keyCode == 13){
    Shiny.onInputChange("keyPressed", Math.random());
  }
});
'

shinyApp(
  ui = bootstrapPage(

    tags$script(js),

    textInput("title", label = "Title"),

    plotOutput("ggplot")
  ),

  server = function(input, output, session){

    Title <- reactiveVal()

    observeEvent(input[["keyPressed"]], {
      Title(input[["title"]])
    })

    output[["ggplot"]] <- renderPlot({
      ggplot(iris, aes(x=Sepal.Length, y=Sepal.Width)) +
        geom_point() +
        ggtitle(Title())
    })

  }
)

Explanations:

This Javascript code:

$(document).on("keyup", function(e) {
  if(e.keyCode == 13){
    Shiny.onInputChange("keyPressed", Math.random());
  }
});

creates a new Shiny input, namely input$keyPressed which receives a random number when the "Return" key is pressed anywhere.

Then I define a reactive value which takes the value input$title given in the textbox by the user, only when input$keyPressed changes:

Title <- reactiveVal()

observeEvent(input[["keyPressed"]], {
  Title(input[["title"]])
})

And finally I pass this reactive value to ggtitle:

output[["ggplot"]] <- renderPlot({
  ggplot(iris, aes(x=Sepal.Length, y=Sepal.Width)) +
    geom_point() +
    ggtitle(Title())
})