Action button/link — actionButton
R/input-action.R
  Description
Creates an action button or link whose value is initially zero, and increments by one each time it is pressed.
Arguments
- inputId
- The - inputslot that will be used to access the value.
- label
- The contents of the button or link--usually a text label, but you could also use any other HTML, like an image. 
- icon
- An optional - icon()to appear on the button.
- width
- The width of the input, e.g. - '400px', or- '100%'; see- validateCssUnit().
- disabled
- If - TRUE, the button will not be clickable. Use- updateActionButton()to dynamically enable/disable the button.
- ...
- Named attributes to be applied to the button or link. 
Server value
An integer of class "shinyActionButtonValue". This class differs from
ordinary integers in that a value of 0 is considered "falsy".
This implies two things:
- Event handlers (e.g., - observeEvent(),- eventReactive()) won't execute on initial load.
- Input validation (e.g., - req(),- need()) will fail on initial load.
See also
observeEvent() and eventReactive()
Other input elements: 
checkboxGroupInput(),
checkboxInput(),
dateInput(),
dateRangeInput(),
fileInput(),
numericInput(),
passwordInput(),
radioButtons(),
selectInput(),
sliderInput(),
submitButton(),
textAreaInput(),
textInput(),
varSelectInput()
Examples
## Only run examples in interactive R sessions
if (interactive()) {
ui <- fluidPage(
  sliderInput("obs", "Number of observations", 0, 1000, 500),
  actionButton("goButton", "Go!", class = "btn-success"),
  plotOutput("distPlot")
)
server <- function(input, output) {
  output$distPlot <- renderPlot({
    # Take a dependency on input$goButton. This will run once initially,
    # because the value changes from NULL to 0.
    input$goButton
    # Use isolate() to avoid dependency on input$obs
    dist <- isolate(rnorm(input$obs))
    hist(dist)
  })
}
shinyApp(ui, server)
}
## Example of adding extra class values
actionButton("largeButton", "Large Primary Button", class = "btn-primary btn-lg")
actionLink("infoLink", "Information Link", class = "btn-info")