actionButton change color/icon

gistfile1.txt

library(shiny)
library(shinyjs)

ui <- fluidPage(
  useShinyjs(),
  sliderInput("slide","", 1,100,1,1),
  actionButton("act", "Init label", icon = icon("check"), width = "300px")
)

server <- function(input, output, session) {
  observe({
    if (input$slide < 30) {
      icon = "play-circle"
      col = "red"
    } else if  (input$slide < 50) {
      icon = "alipay"
      col = "orange"
    } else if  (input$slide < 70) {
      icon = "ad"
      col = "yellow"
    } else if  (input$slide < 90) {
      icon = "angle-down"
      col = "green"
    } else {
      icon = "arrow-up"
      col = "darkgreen"
    }
    
    updateActionButton(session, "act", label = col, icon = icon(icon))
    runjs(
      paste0("$('#act').css({'background-color': '",col,"', 'color': 'white'})")
    )
  })
}

shinyApp(ui, server)