In running the below reproducible code, I'm trying to extract specific node elements from a jsTree (using the jsTreeR package) into a data frame. Similar to what was done in related post that used sortable DnD instead of jstree at How to pull list elements from HTML/CSS and into an R data frame?

Any ideas for extracting specific node elements from a jsTree for use in a dataframe?

This is so further R operations can be performed on those dragged-in (or better said, copied over) elements.

The image at the bottom better explains.

Reproducible code (I commented out my attempts to resolve this in the below):

library(jsTreeR)
library(shiny)

nodes <- list(
  list(
    text = "Menu",
    state = list(opened = TRUE),
    children = list(
      list(text = "A", type = "moveable", state = list(disabled = TRUE)),
      list(text = "B", type = "moveable", state = list(disabled = TRUE))
    )
  ),
  list(text = "Drag here:", 
       type = "target", 
       state = list(opened = TRUE)
       )
)

checkCallback <- JS(
  "function(operation, node, parent, position, more) { console.log(node);",
  "  if(operation === 'copy_node') {",
  "    if(parent.id === '#' || node.parent !== 'j1_1' || parent.type !== 'target') {",
  "      return false;", # prevent moving an item above or below the root
  "    }",               # and moving inside an item except a 'target' item
  "  }",
  "  return true;",      # allow everything else
  "}"
)
  
dnd <- list(
  always_copy = TRUE,
  is_draggable = JS(
    "function(node) {",
    "  return node[0].type === 'moveable';",
    "}"
  )
)

ui <- fluidPage(
  tags$head(
    tags$script(
      HTML(
        script <- 
          '
            $(document).ready(function(){
              $("#mytree").on("copy_node.jstree", function(e, data){
                var instance = data.new_instance;
                var node = data.node;
                var id = node.id;
                var text = node.text;
                var index = $("#"+id).index() + 1;
                instance.rename_node(node, index + ". " + text);
              })
            });
          '
      )
    )
  ),
  
  jstreeOutput("mytree"),
  # tableOutput("table1")
  
  )  

server <- function(input, output){
  output[["mytree"]] <- renderJstree({
    jstree(
      nodes, 
      dragAndDrop = TRUE, 
      dnd = dnd, 
      checkCallback = checkCallback,
      types = list(moveable = list(), 
                   target = list()),
    )
  })

  # draggedElements <- reactive({
  #   data.frame(data = paste0(seq_along(jstreeOutput("mytree")), ". ", jstreeOutput("mytree")))
  # })
  
  # output$table1 <- renderTable({draggedElements()})
  
}  

shinyApp(ui, server)

First, unrelated to this question, I added the option inside_pos="last" in the drag-and-drop handler:

dnd <- list(
  always_copy = TRUE,
  inside_pos = "last",
  is_draggable = JS(
    "function(node) {",
    "  return node[0].type === 'moveable';",
    "}"
  )
)

With this option, you can drop a node on the node "Drag here" and it automatically goes to the last position (see the GIF). Very convenient.

Now, for your question. This is a job for Shiny.setInputValue. Modify the script:

script <- '
$(document).ready(function(){
  $("#mytree").on("copy_node.jstree", function(e, data){
    var instance = data.new_instance;
    var node = data.node;
    var id = node.id;
    var index = $("#"+id).index() + 1;
    var text = index + ". " + node.text;
    Shiny.setInputValue("choice", text);
    instance.rename_node(node, text);
  })
});
'

And here is the Shiny app:

ui <- fluidPage(
  tags$head(tags$script(HTML(script))),
  fluidRow(
    column(
      width = 6,
      jstreeOutput("mytree")
    ),
    column(
      width = 6,
      verbatimTextOutput("choices")
    )
  )
)

server <- function(input, output, session){

  output[["mytree"]] <- renderJstree(mytree)

  choices <- reactiveVal(data.frame(choice = character(0)))

  observeEvent(input[["choice"]], {
    choices(
      rbind(
        choices(),
        data.frame(choice = input[["choice"]])
      )
    )
  })

  output[["choices"]] <- renderPrint({
    choices()
  })

}

EDIT: deletion

checkCallback <- JS(
  "function(operation, node, parent, position, more) { ",
  "  if(operation === 'copy_node') {",
  "    if(parent.id === '#' || node.parent !== 'j1_1' || parent.type !== 'target') {",
  "      return false;", # prevent moving an item above or below the root
  "    }",               # and moving inside an item except a 'target' item
  "  }",
  "  if(operation === 'delete_node') {",
  "    Shiny.setInputValue('deletion', position + 1);",
  "  }",
  "  return true;",      # allow everything else
  "}"
)

server <- function(input, output, session){

  output[["mytree"]] <- renderJstree(mytree)

  Choices <- reactiveVal(data.frame(choice = character(0)))

  observeEvent(input[["choice"]], {
    Choices(
      rbind(
        Choices(),
        data.frame(choice = input[["choice"]])
      )
    )
  })

  observeEvent(input[["deletion"]], {
    Choices(
      Choices()[-input[["deletion"]], , drop = FALSE]
    )
  })

  output[["choices"]] <- renderPrint({
    Choices()
  })

}

Full app, with icons and the proton theme:

library(jsTreeR)

nodes <- list(
  list(
    text = "Menu",
    state = list(opened = TRUE),
    a_attr = list(style = "font-weight: bold;"),
    children = list(
      list(
        text = "Dog",
        type = "moveable",
        state = list(disabled = TRUE),
        icon = "fas fa-dog"
      ),
      list(
        text = "Cat",
        type = "moveable",
        state = list(disabled = TRUE),
        icon = "fas fa-cat"
      ),
      list(
        text = "Fish",
        type = "moveable",
        state = list(disabled = TRUE),
        icon = "fas fa-fish"
      )
    )
  ),
  list(
    text = ">>> Drag here <<<",
    type = "target",
    state = list(opened = TRUE),
    a_attr = list(style = "font-weight: bold;")
  )
)

checkCallback <- JS(
  "function(operation, node, parent, position, more) { ",
  "  if(operation === 'copy_node') {",
  "    if(parent.id === '#' || node.parent !== 'j1_1' || parent.type !== 'target') {",
  "      return false;", # prevent moving an item above or below the root
  "    }",               # and moving inside an item except a 'target' item
  "  }",
  "  if(operation === 'delete_node') {",
  "    Shiny.setInputValue('deletion', position + 1);",
  "  }",
  "  return true;",      # allow everything else
  "}"
)

dnd <- list(
  always_copy = TRUE,
  inside_pos = "last",
  is_draggable = JS(
    "function(node) {",
    "  return node[0].type === 'moveable';",
    "}"
  )
)

customMenu <- JS(
  "function customMenu(node) {",
  "  var tree = $('#mytree').jstree(true);", # 'mytree' is the Shiny id or the elementId
  "  var items = {",
  "    'delete' : {",
  "      'label'  : 'Delete',",
  "      'action' : function (obj) { tree.delete_node(node); },",
  "      'icon'   : 'glyphicon glyphicon-trash'",
  "     }",
  "  }",
  "  return items;",
  "}")


mytree <- jstree(
  nodes, dragAndDrop = TRUE, dnd = dnd, checkCallback = checkCallback,
  types = list(moveable = list(), target = list()),
  contextMenu = list(items = customMenu),
  theme = "proton"
)

script <- '
$(document).ready(function(){
  $("#mytree").on("copy_node.jstree", function(e, data){
    var instance = data.new_instance;
    var node = data.node;
    var id = node.id;
    var index = $("#"+id).index() + 1;
    var text = index + ". " + node.text;
    Shiny.setInputValue("choice", text);
    instance.rename_node(node, text);
  });
});
'

library(shiny)
ui <- fluidPage(
  tags$head(tags$script(HTML(script))),
  fluidRow(
    column(
      width = 4,
      jstreeOutput("mytree")
    ),
    column(
      width = 8,
      verbatimTextOutput("choices")
    )
  )
)

server <- function(input, output, session){

  output[["mytree"]] <- renderJstree(mytree)

  Choices <- reactiveVal(data.frame(choice = character(0)))

  observeEvent(input[["choice"]], {
    Choices(
      rbind(
        Choices(),
        data.frame(choice = input[["choice"]])
      )
    )
  })

  observeEvent(input[["deletion"]], {
    Choices(
      Choices()[-input[["deletion"]], , drop = FALSE]
    )
  })

  output[["choices"]] <- renderPrint({
    Choices()
  })

}

shinyApp(ui, server)