server.r:

library(shiny)
library(shinydashboard)
library(leaflet)
library(rgdal)
library(utf8)
library(sf)
library(rgeos)

shinyServer(function(input, output, session){


 # create reactive upload file function to store data
 uploadShpfile <- reactive({
   if (!is.null(input$shp)) {
     shpDF <- input$shp
     pwd <- getwd()
     updir <- dirname(shpDF$datapath[1])
     setwd(updir)
     for (i in 1:nrow(shpDF)) {
       file.rename(shpDF$datapath[i], shpDF$name[i])
     }
     shpName <- shpDF$name[grep(x = shpDF$name, pattern = "*.shp")]
     shpPath <- paste(updir, shpName, sep = "/")
     setwd(pwd)
     shpFile <- readOGR(shpPath)
     shpFile <- spTransform(shpFile,CRS("+proj=longlat +datum=NAD83 +no_defs +ellps=GRS80 +towgs84=0,0,0"))
   }
 })

 output$map <- renderLeaflet({

   leaflet() %>%
     addProviderTiles("Esri.WorldImagery", group = "Esri World Imagery", options = providerTileOptions(minZoom = 2, maxZoom = 17)) %>%
     addTiles(group = "OSM", options = providerTileOptions(minZoom = 2, maxZoom = 17)) %>%
     addMiniMap(toggleDisplay = T) %>%
     setView(lng = 97.963,lat = 20.380, zoom = 6 ) %>%
     addLayersControl(baseGroups = c("Esri World Imagery", "OSM"))
 })

 observeEvent(input$shp, {
   if (!is.null(uploadShpfile())) {
     cent <- gCentroid(spgeom = uploadShpfile(), byid = FALSE)
     leafletProxy("map") %>%
       addPolygons(data = uploadShpfile()) %>%
       setView(lat = slot(cent, "coords")[[2]], lng = slot(cent, "coords")[[1]], zoom = 7)
   }
 })
})