renderUI as a alternative

renderUI.r

library (shiny)

server <- function(input, output) {

    rv <- reactiveValues(numFields = 1)
    #
    # start with one input box
    #
    output$fieldsUI <- renderUI(textInput("textInput1", "Input #1", 67))
    #
    # each time the button is clicked, increase the reactive value and add a new text input

    fields_fn <- function(i){
        latest_n = paste0('sliderInput', i)
        tagList(
            textInput(paste0("textInput",   i), paste0("Input #", i), i + 10),
            sliderInput(paste0("sliderInput", i), paste0("Slide #", i), 1, 10, i),
            input[[latest_n]] * 2
        )
    }
    

    observeEvent(input$addField,{
        rv$numFields <- rv$numFields + 1
        latest_n <- paste0('fieldsUI', '')
        output[[latest_n]] <- renderUI({ 
#        output$fieldsUI <- renderUI({
            lapply(1:rv$numFields,
                fields_fn
            )
        })
    })
}

ui <- fluidPage(sidebarLayout(
    sidebarPanel(
        actionButton("addField", "Add text input box")
    ),
    mainPanel(
        uiOutput("fieldsUI")
    )
))

shinyApp(ui, server)
# eof