shiny app for drag event using L.Path.Drag. Need to install this fork: https://github.com/byzheng/leaflet/

app.R

library(leaflet)
library(shiny)

ui <- fluidPage(
  leafletOutput('map'),
  verbatimTextOutput('summary')
)

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

  output$summary <- renderPrint({
    #event <- input$map_shape_click
    #print(paste(paste(names(event), event, sep = '='), collapse = ', '))
    # event <- input$map_shape_dragstart
    # print(paste(paste(names(event), event, sep = '='), collapse = ', '))
    #
    #
    # event <- input$map_shape_drag
    # print(paste(paste(names(event), event, sep = '='), collapse = ', '))

    event <- input$map_shape_dragend
    # print(paste(paste(names(event), event, sep = '='), collapse = ', '))
    print(event)
  })

  output$map <- renderLeaflet({

    leaflet() %>%
      addTiles() %>%
      addPolygons(
        lng = c(0, 10, 10, 0, 0),
        lat = c(0, 0, 10, 10, 0),
        options = pathOptions(draggable = TRUE),
        layerId = 'Polygon_1'

      )

  })
}


shinyApp(ui, server)