using data_index reactive for controlling output

example.R

library(shiny)
library(reactable)
ui <- fluidPage(
    reactableOutput("dummy")    
)

server <- function(input, output, session) {
    
    data <- tibble::tibble(x = letters[1:3], y = 1:3, z = c(3, 7, 11))
    
    output$dummy <- renderReactable({
        reactable(
            data,
            columns = list(z = colDef(show = FALSE)),
            details = function(index) {
                tags$div(style = "height: 50px;", actionButton("action", "action"))
            },
            selection = "single",
            onClick = "select"
        )
    })
    
   data_index <- reactive({
       getReactableState("dummy", "selected")
   }) 
    
    observeEvent(input$action, {
        message("the value of data_index is ", data_index())
        showModal(modalDialog(
            title = "example",
            tags$h1(paste0("The secret value is ", data[["z"]][data_index()])),
            easyClose = FALSE,
            footer = tagList(actionButton("ok", "ok"))
        ))
    })
    
    observeEvent(input$ok, {
        removeModal()
        reactable::updateReactable("dummy", selected = NA, expanded = FALSE)
    })
}

shinyApp(ui, server)