How to manually collapse a box in shiny dashboard

I'm trying to collapse a box manually when something happens. It seems that I only need to add the class "collapsed-box" to the box, I tried to use the shinyjs function addClass, but I don't know how to do that becuase a box doesn't have an id. Here as simple basic code that can be used to test possible solutions:

library(shinydashboard)

ui <- dashboardPage(
  dashboardHeader(),
  dashboardSidebar(),
  dashboardBody(
      box(collapsible = TRUE,p("Test")),
      actionButton("bt1", "Collapse")
  )
)

server <- function(input, output) {
  observeEvent(input$bt1, {
    # collapse the box
  })
}

shinyApp(ui, server)

I've never tried using boxes before so keep in mind that my answer might be very narrow minded. But I took a quick look and it looks like simply setting the "collapsed-box" class on the box does not actually make the box collapse. So instead my next thought was to actually click the collapse button programatically.

As you said, there isn't an identifier associated with the box, so my solution was to add an id argument to box. I initially expected that to be the id of the box, but instead it looks like that id is given to an element inside the box. No problem - it just means that in order to select the collapse button, we need to take the id, look up the DOM tree to find the box element, and then look back down the DOM tree to find the button.

I hope everything I said makes sense. Even if it doesn't, this code should still work and will hopefully make things a little more clear :)

library(shiny)
library(shinydashboard)
library(shinyjs)

jscode <- "
shinyjs.collapse = function(boxid) {
$('#' + boxid).closest('.box').find('[data-widget=collapse]').click();
}
"

ui <- dashboardPage(
  dashboardHeader(),
  dashboardSidebar(),
  dashboardBody(
    useShinyjs(),
    extendShinyjs(text = jscode),
    actionButton("bt1", "Collapse box1"),
    actionButton("bt2", "Collapse box2"),
    br(), br(),
    box(id = "box1", collapsible = TRUE, p("Box 1")),
    box(id = "box2", collapsible = TRUE, p("Box 2"))
  )
)

server <- function(input, output) {
  observeEvent(input$bt1, {
    js$collapse("box1")
  })
  observeEvent(input$bt2, {
    js$collapse("box2")
  })
}

shinyApp(ui, server)