Disable button in shiny while plot is loading

Is it possible to disable a button in shiny while a plot / a reactive element is loading? I know shinyjs can disable and enable input elements, but I don't know how to set up the connection to a loading plot / reactive element. The example is based on the Single-file shiny apps page. I just added a button and the isolated part. Solutions that are not based on shinyjs are also appreciated :)

library(shiny)
server <- function(input, output) {
  output$distPlot <- renderPlot({
    input$button

    isolate(
      hist(rnorm(input$obs), col = 'darkgray', border = 'white')
    )
  })
}

ui <- fluidPage(
  shinyjs::useShinyjs(),
  sidebarLayout(
    sidebarPanel(
      sliderInput("obs", "Number of observations:", min = 10, max = 500, value = 100),
      actionButton("button", "OK!")
    ),
    mainPanel(plotOutput("distPlot"))
  )
)

shinyApp(ui = ui, server = server)