How to make the horizontal scrollbar visible in DT::datatable - r

Question

Using R shiny & DT package, I am creating certain tables. The number of columns vary as per user input & is not fixed. I have included the following code snippet to include a horizontal scrollbar so that when the number of columns is large, the user can scroll through the columns that are not directly visible.
server.R:
output$results <- DT::renderDataTable({
DT::datatable(data = datasetInput(),
options = list(scrollX = TRUE,...)
)
})
<code reduced for brevity>
Using the above code, the Horizontal scrollbar is not visible at first but appears when I click on a row and hit right arrow on my keyboard. Is there any way the scroll bar becomes visible as soon as the table is fired up, no matter how many columns I have, and I can drag the scrollbar using the mouse pointer?
Update:
I tried the code in the answer below and this is what I see - no horizontal scrollbar.

Answer 1

I don't think you can (or should) force a scrollbar easily if you don't need one, but the above code works fine for me, it shows a scrollbar when the page initializes. Maybe the problem is with the data or something else.
Here's a minimal example that has a horizontal scrollbar on page load
runApp(shinyApp(
ui = fluidPage(
DT::dataTableOutput("results", width = 300)
),
server = function(input, output, session) {
output$results <- DT::renderDataTable(
mtcars,
options = list(scrollX = TRUE)
)
}
))

Answer 2

Try this:
DT::datatable(sta, options = list(
pageLength=50, scrollX='400px'), filter = 'top')

Answer 3

I would have done this way also:
datasetInput1 <- reactive({
infile <- input$file1
if(is.null(infile))
return(NULL)
else
m <- read.csv(infile$datapath, header = input$header)
return ( DT::datatable(m, extensions = 'Scroller', options = list(deferRender = F, dom = 't',
columnDefs = list(list(className = 'dt-center',
targets = 5)),
scrollY = 300, scroller = TRUE, scrollX = T,
pageLength = 5))
)
})