simple shiny dashboard

id_maker.R

id_maker <- function(prefix = make_random_string()) {
  function(id) {
    paste(prefix, id, sep = "_")
  }
}

make_random_string <- function(n=1, len=12, chars=c(0:9, letters, LETTERS)) {
  randomString <- sapply(seq(n), function(i) {
    paste(sample(chars, len, replace = TRUE), collapse = "")
  })
  randomString
}

server.R

# server.R
library(shiny)

source("tab1_page.R")
source("tab2_page.R")
source("tab3_page.R")
source("id_maker.R")

shinyServer(function(input, output, session) {
  output$tab1_page <- renderUI(create_tab1_page(session = session))
  output$tab2_page <- renderUI(create_tab2_page(session = session))
  output$tab3_page <- renderUI(create_tab3_page(session = session))
})

tab1_page.R

# tab1_page.R
create_tab1_page <- function(session) {
  id <- id_maker()
  tab_page <- fluidPage(
    "this is tab1 page",
    selectInput(id('select_input'), "select a letter", choices = letters),
    verbatimTextOutput(id('text_output'))
  )
  on.exit({
    input <- session$input
    output <- session$output
    output[[id('text_output')]] <- renderText({
      input[[id('select_input')]]
    })
  })
  return(tab_page)
}

tab2_page.R

# tab2_page.R
create_tab2_page <- function(session) {
  id <- id_maker()
  tab_page <- fluidPage(
    "this is tab2 page"
  )
  return(tab_page)
}

tab3_page.R

# tab3_page.R
create_tab3_page <- function(session) {
  id <- id_maker()
  tab_page <- fluidPage(
    "this is tab3 page"
  )
  return(tab_page)
}

ui.R

# ui.R
library(shiny)
library(shinydashboard)

header <- dashboardHeader(
  title = "shiny app"
)

sidebar <- dashboardSidebar(
  sidebarMenu(
    menuItem("tab1", tabName = "tab1", icon = icon("pie-chart")),
    menuItem("tab2", tabName = "tab2", icon = icon("retweet")),
    menuItem("tab3", tabName = "tab3", icon = icon("users"))
  )
)

body <- dashboardBody(
  tabItems(
    tabItem(tabName = "tab1", uiOutput("tab1_page")),
    tabItem(tabName = "tab2", uiOutput("tab2_page")),
    tabItem(tabName = "tab3", uiOutput("tab3_page"))
  )
)

shinyUI(dashboardPage(header, sidebar, body))