Demo in Progress (very buggy) on sliderInput with numericInput for min/max

server.R

# server.R

library("shiny")

shinyServer(
  function(input, output, session) {

    # Reactive slider
    v <- reactiveValues(min = -5, max = +5, status = 0)

    observe({
        input$sliderMin
        v$min <- isolate(input$sliderMin)
    })
    
    observe({
        input$sliderMax
        v$max <- isolate(input$sliderMax)
    })
    
    # reactive slider
    slider <- reactive({
      if (is.null(input$sliderMin) || is.na(input$sliderMin)) {
        min <- -5
      } else {
        min <- isolate(input$sliderMin)
      }
      if (is.null(input$sliderMax) || is.na(input$sliderMax)) {
        max <- +5
      } else {
        max <- isolate(input$sliderMax)
      }
      Id <- paste0("Id",sample(1:100000,1,replace=TRUE)) # unique Id needed?
      value <- ((min+max)/2)
      if (!(min < max) || !(is.numeric(min)) || !(is.numeric(max))) {
        return(list(min=-5, max=+5, Id=Id, value=0))
      } else {
        return(list(min=min, max=max, Id=Id, value=value))
      }
    })
    
    # output slider
    output$sliderUI <- renderUI({    
      list(
        sliderInput(inputId = slider()$Id, label = h4("Reactive Slider with user-selected min/max:"), min = slider()$min, max = slider()$max, value = slider()$value)
        ,
        numericInput(inputId = "sliderMin", label = h4(""), value = slider()$min)
        ,
        numericInput(inputId = "sliderMax", label = h4(""), value = slider()$max)
      )
    })    
        
    # output value from sliderInput
    output$sliderValueUI.hide <- renderUI({
        if (is.null(input$sliderMin) || is.null(input$sliderMax)) {
          return()
        } else {
          list(
            br(), tags$hr()
          , HTML("Slider inputId:"), paste(slider()$Id), br()
          , HTML("Value read from min box:"), paste(input$sliderMin), br()
          , HTML("Value read from max box:"), paste(input$sliderMax), br()
          , tags$hr()
          )
        }
    })

    
  }
)

ui.R

# ui.R

library("shiny")

shinyUI(
  basicPage(
    mainPanel(
      tags$head(tags$style(type = "text/css"
      , "#sliderMin {width: 30px; height: 15px; float: left;}"
      , "#sliderMax {width: 30px; height: 15px; float: right;}"
      ))
      ,
      uiOutput("sliderUI")
      ,
      uiOutput("sliderValueUI")
    )
  )
)