Dynamic Animation Speed

app.R

library("shiny")

ui <- fluidPage(
  includeScript('shiny-events.js'),

  numericInput("min", "Min", value = 0, min = 0, max = 10),
  numericInput("max", "Max", value = 100, min = 100, max = 200),
  sliderInput("speed", "Animation Speed", value = 100, ticks = FALSE, round = 50, min = 50, max = 1000),
  uiOutput('slider_div'),
  br(),
  htmlOutput('displaySpeed')
)

server <- function(input, output, session) {

  output$slider_div <- renderUI({

    sliderInput(
        inputId = 'slider'
      , label   = 'Slider'
      , min     = input$min
      , max     = input$max
      , value   = isolate(animation$value)
      , animate = animationOptions(interval = animation$speed, loop = TRUE)
    )

  })

  # update animation interval 
  animation <- reactiveValues(speed = 100, value = 1)

  observeEvent(input$speed, {
    invalidateLater(500, session)

    animation$value <- input$slider
    animation$speed <- input$speed
  })

  output$displaySpeed <- renderText({
    HTML("Current interval:", animation$speed)
  })

  observeEvent(input$speed, {
    session$sendCustomMessage('resume', TRUE)
  })

  observeEvent(input$min | input$max, {
    animation$value <- input$slider
  })
}

shinyApp(ui, server)

shiny-events.js

$(function() {
    var renders = 0;
    var press_play = false;
    $(document).on({

        // COULD ALSO DO $('#slider_div').on('shiny:value', function() {...})
        'shiny:value': function(event) {
            switch (event.name) {
                case 'slider_div':
                    // WONT RESUME IF THE RENDER WAS DUE TO SOMETHING ELSE
                    if (renders > 0 && press_play) {
                        setTimeout(function() {
                            $('.slider-animate-button').click();
                        }, 200);

                        press_play = false;
                    } else {
                      renders = 1;
                    }
                    break;

                default:
            } 
        }

    });


    Shiny.addCustomMessageHandler('resume', function(message) {
        press_play = true;
    });
});