当在R shiny中调用downloadHandler函数时，如何生成一个弹出窗口，并提示选择下载哪个对象？

library(shiny)

ui <- fluidPage(
  actionButton("downloadBtn", "Download"),
  tags$script(
    HTML(
      "
      $(document).on('click', '#downloadBtn', function() {
        var modal = $('<div>').attr('id', 'downloadModal').addClass('modal fade');
        var modalDialog = $('<div>').addClass('modal-dialog');
        var modalContent = $('<div>').addClass('modal-content');
        var modalHeader = $('<div>').addClass('modal-header').html('<h4 class=\"modal-title\">Select Object to Download</h4>');
        var modalBody = $('<div>').addClass('modal-body');
        var selectInput = $('<select>').attr('id', 'downloadSelect').addClass('form-control');
        var option1 = $('<option>').attr('value', 'object1').text('Object 1');
        var option2 = $('<option>').attr('value', 'object2').text('Object 2');
        var modalFooter = $('<div>').addClass('modal-footer');
        var downloadBtn = $('<button>').attr('id', 'confirmDownload').addClass('btn btn-primary').text('Download');
        
        modalBody.append(selectInput.append(option1).append(option2));
        modalFooter.append(downloadBtn);
        modalContent.append(modalHeader).append(modalBody).append(modalFooter);
        modalDialog.append(modalContent);
        modal.append(modalDialog);
        
        Shiny.onInputChange('showModal', true);
        $(document.body).append(modal);
        $('#downloadModal').modal('show');
      });
      
      $(document).on('click', '#confirmDownload', function() {
        var selectedObject = $('#downloadSelect').val();
        Shiny.onInputChange('selectedObject', selectedObject);
        $('#downloadModal').modal('hide');
      });
      
      Shiny.addCustomMessageHandler('closeModal', function(message) {
        $('#downloadModal').modal('hide');
      });
      "
    )
  )
)

server <- function(input, output, session) {
  observeEvent(input$selectedObject, {
    # 根据选择的对象进行相应的下载操作
    if (input$selectedObject == "object1") {
      # 下载对象1
    } else if (input$selectedObject == "object2") {
      # 下载对象2
    }
    
    # 下载完成后关闭弹出窗口
    session$sendCustomMessage("closeModal", "")
  })
}

shinyApp(ui, server)